WO1983000787A1 - Systeme de transfert de signaux modules avec un rendement maximum en utilisant des systemes de lignes - Google Patents

Systeme de transfert de signaux modules avec un rendement maximum en utilisant des systemes de lignes Download PDF

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Publication number
WO1983000787A1
WO1983000787A1 PCT/US1981/001147 US8101147W WO8300787A1 WO 1983000787 A1 WO1983000787 A1 WO 1983000787A1 US 8101147 W US8101147 W US 8101147W WO 8300787 A1 WO8300787 A1 WO 8300787A1
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WO
WIPO (PCT)
Prior art keywords
signal
audio
signals
output
frequency
Prior art date
Application number
PCT/US1981/001147
Other languages
English (en)
Inventor
Alfred F. Eberhardt
Marvin Coghill
Original Assignee
Bloy, Graham, Philip
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Bloy, Graham, Philip filed Critical Bloy, Graham, Philip
Priority to GB08310309A priority Critical patent/GB2118408B/en
Priority to JP81503040A priority patent/JPS59500297A/ja
Priority to PCT/US1981/001147 priority patent/WO1983000787A1/fr
Priority to DE19813152946 priority patent/DE3152946T1/de
Priority to EP19810902508 priority patent/EP0086777A1/fr
Priority to AU75855/81A priority patent/AU7585581A/en
Publication of WO1983000787A1 publication Critical patent/WO1983000787A1/fr

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Classifications

    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03G—CONTROL OF AMPLIFICATION
    • H03G7/00—Volume compression or expansion in amplifiers
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03G—CONTROL OF AMPLIFICATION
    • H03G5/00—Tone control or bandwidth control in amplifiers
    • H03G5/02—Manually-operated control
    • H03G5/04—Manually-operated control in untuned amplifiers
    • H—ELECTRICITY
    • H03—ELECTRONIC CIRCUITRY
    • H03G—CONTROL OF AMPLIFICATION
    • H03G9/00—Combinations of two or more types of control, e.g. gain control and tone control
    • H03G9/02—Combinations of two or more types of control, e.g. gain control and tone control in untuned amplifiers
    • H03G9/025—Combinations of two or more types of control, e.g. gain control and tone control in untuned amplifiers frequency-dependent volume compression or expansion, e.g. multiple-band systems
    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04B—TRANSMISSION
    • H04B1/00—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission
    • H04B1/62—Details of transmission systems, not covered by a single one of groups H04B3/00 - H04B13/00; Details of transmission systems not characterised by the medium used for transmission for providing a predistortion of the signal in the transmitter and corresponding correction in the receiver, e.g. for improving the signal/noise ratio
    • H04B1/64—Volume compression or expansion arrangements

Definitions

  • the present invention relates to audio processing and modulation systems and, more particularly, to an improved signal processing system intended for maximizing the efficiency of line system transmission or transferring especially of audio frequency signals, as in telephony, for providing high modulation levels and for enhancing signal intelligibility and clarity while avoiding loss of audio dynamics.
  • AM and FM utilize a constant carrier principal while SSB has a direct audio into power out relationship and is not a constant carrier mode of transmission when the carrier is suppressed, as is quite common.
  • Frequency Modulation FM
  • the dynamic content of the signal and the audio bandwidth of the signal are directly proportional to the amount of deviation allowed to be imposed on the carrier.
  • an audio bandwidth of 3 kcs. may be imposed.
  • dynamic harmonics of voice characteristics are restricted and lost.
  • Dynamic amplitude can be defined as the varying level of audio received by a modulation stage in any mode of modulation.
  • the human voice is made up by a complex structure of harmonics, the main bands of harmonics falling within a 3 kHz bandwidth.
  • a speech band-pass frequency range commonly selected is 300 Hz to 3000 Hz, and all other harmonics are generally suppressed.
  • these out-of-band harmonics define voice character and, thus, intelligibility.
  • the suppressed harmonics fall in such a wide spectrum that if the entire speech harmonic make-up were to be transmitted, a line transmission band ⁇ width of some 15 kHz would be required. With modern narrow band voice line transmission systems, this would become impossible.
  • a syste for interfacing audio processing circuitry with line systems should be designed to handle these various modes of line transferred information.
  • frequency modulation is also used.
  • interfacing should be able to prove a system contains demodulation and/or modulation for AM, FM, CW and SSB modes of transmission over a communication link.
  • An object of the invention is to provide a system for maximizing the efficiency of transfer of modulated signals in general and especially audio frequency energy, and particularly such a system utilizing transmission line systems.
  • a further object of the invention is to provide such a system useful with modulation systems.
  • a further object of the invention is to provide such a system for providing transfer of audio frequency signals, especially over transmission lines, in such a way that high average modulation power is attainable.
  • a still further object of the invention is to provide such a system for providing transfer, especially over transmission lines, of signals particularly those of audio frequency, to enhance signal intelligibility and clarity while preventing loss of dynamics.
  • Another object of the invention is to provide such a system which allows the processing of signals demodulated from received line transmitted signals in order to re- trieve signals, particularly audio signals, with effectively high signal-to-noise ratios even where there is high noise level associated with the received line transmitted signals.
  • a further object of the invention is to provide such a system which can be utilized for processing of various types of signals, e.g., voice, tones, data., etc., prior to their use in modulating a line transmitted signal, as well as processing demodulated audio frequency signals upon reception of a line transmitted signal.
  • signals e.g., voice, tones, data., etc.
  • An additional object of the invention is the provision of such a system which is useful with various modulation systems and modulation stages to achieve maximum carrier utilization, with result in increase in effective line transmitted power and clarity.
  • Another object of the invention is the provision of such a system which processes audio frequency signals in such a way as to reconstitute wide frequency spectrum dynamic associated with voice and other audio frequency signals used, inter alia, for modulation of transmission lines, and which does so by recovery and amplification to audible levels of harmonics otherwise suppressed or filtered.
  • a related further object of the invention is the pro ⁇ vision of such a system which permits transmission of -audio signals with high average modulation levels, approaching 100% average modulation, but without customary dramatic loss of audio dynamics and intelligibility.
  • An object of the invention also is the provision of such a system which can be utilized in the fields of line transmission not only of speech but also high speed data, teletype, facsimile, and other modes of data communication, and when so utilized in data communication, may be advant ⁇ ageously part of a data communication link for reducing data drop-out.
  • a related further object of the invention is the pro- vision of such a system utilizing various visual indicators for keeping the user constantly informed and aware of the extent to which signals are properly processed through the system.
  • An additional object of the invention is the provision of such a system which accepts substantially any low level signal within the audio frequency spectrum while according to the user the options of utilizing and emphasizing various components of the audio spectrum, and of selective ⁇ ly filtering and/or amplifying the input and/or output signals.
  • Another object of the invention is the provision of such a system in which the output of the audio signals processed through the system can be preset in amplitude to be fed to any modulation stage currently used in conventional line communication systems.
  • a further object of the invention is the provision of such a system which is especially of advantage in connection with narrow band VHF line transmission, making possible extraordinarily narrow band transmission containin full dynamic characteristics of audio frequency signals so processed while keeping a very high character level of modulation.
  • a further object of the invention is the provision of such a system which provides interfacing with telephone lines providing impedance matching and automatic selective direction control for transmission and receiving functions.
  • a signal transfer and processing system of the invention includes interface circuitry and processing circuitry.
  • the processing circuitry includes a signal input for receiving signals (such as audio frequency, telephone, digital, encypted, or data signals, etc.) to be processed. These signals are supplied to a bandpass input filter and, thus filtered, to a primary active frequency control.
  • the output of the latter drives a primary voltage compressor which selectively limits signal dynamics to a predetermined window, being controllably preset and driven with different bands of amplitude determined by the primary frequency control to maximum compression levels indicated by a visual indicator.
  • the output of the compressor is presented to a secondary active frequency control which drives a secondary dynamic compresso with different audio bands.
  • a second signal indicator indicates maximum compression levels of the latter.
  • An automatic gain control tied to the latter compressor supplie feedback to the primary voltage compressor and also feeds a third visual indicator which displays compressed output voltage as well as average peak dynamic compression.
  • the processed output of the secondary compressor is provided to a bandpass output filter and, sharply attenuated by the latter, is delivered for further use.
  • a high level output stage is also selectively utilized.
  • the AGC feedback signal to the primary compressor limits primary compression as a time-delayed function of increase in the level of the secondary compressor output.
  • the primary and secondary compressors may be regarded as respective first and second dynamic control means, the primary and secondary active frequency controls as respective first and second tonal control means, since both compressors and both active frequency controls are configured for permitting selective controlling of their respective functions.
  • the bandpass input and output filters each may be selectively switched in or out of the signal processing path.
  • the third visual indicator may be a meter having a moving coil-type movement to provide an averaging display.
  • the interface circuitry provides interconnection of said processing circuitry with a transmission line for causing signals transmitted over the transmission line to be automatically directed through the processing circuitry thereby to produce processing of audio frequency signals transmitted over the transmissio line.
  • the interface circuitry includes switching circuits for providing interconnection with telephone lines, for example, and for selectively switching into the system demodulators and modulators for AM, FM, CW and SSB modes of communication.
  • FIGURE 1 is a block diagram of a system constructed in accordance with and embodying the present invention.
  • FIGURE 2 is a block diagram of the system of FIGURE 1 but illustrating certain features thereof in greater functional detail.
  • FIGURE 3 is a block diagram of audio processing circuitry of the system of FIGURE 1.
  • FIGURE 4 is a schematic circuit diagram of a band- pass input filter of the circuitry of FIGURE 1.
  • FIGURE 5 is a schematic circuit diagram of a primary active frequency control circuit of FIGURE 1.
  • FIGURE 6 is a schematic circuit diagram of a primary voltage compressor of the system of FIGURE 1.
  • FIGURE 6A is a block diagram of an integrated circuit device forming part of the primary compressor of FIGURE 6.
  • FIGURE 7 is a schematic circuit diamgram of a secondary active frequency control fo the system of FIGURE 1.
  • FIGURE 8 is a schematic circuit diagram of a secondary dynamic compressor of the system of FIGURE 1.
  • FIGURE 9 is a schematic circuit diagram of a bandpass output filter of the system of FIGURE 1.
  • FIGURE 10 is a schematic circuit diagram of an LED drive circuit including an LED indicator utilized in the system of FIGURE 1.
  • FIGURE 11 is a schematic circuit diagram of circuitry of an automatic gain control as well as meter drive circuitry and a meter for indicating operation performance of the system of FIGURE 1.
  • FIGURE 12 is a schematic circuit diagram of an active filter power supply utilized in the system of FIGURE 1.
  • FIGURE 13 is a schematic circuit diagram of an audio frequency amplifier utilized in the system of FIGURE 1.
  • FIGURE 14 is a graph of a family of curves illustrating operation of certain compressor circuitry of the invention.
  • FIGURE 15 is a graph of a family of curves illustratin the operation of certain amplification circuitry of the invention.
  • FIGURE 16 is a block diagram illustrating a simplex communications configuration of the invention.
  • FIGURE 17 is a simplified block diagram illustrating duplex communications configuration of the invention.
  • transmission line is intended to encompass any of the general class of signal-transmission line systems which either comprise conductive connections (such as twisted pairs, telephone lines, etc.) between system elements which carry signal power or which have other types of transmission line components (such as coaxial cable and waveguide, etc.) for carrying signals of various frequencies but wherein the signals are modulated or otherwise contain audio frequency information or are pulse or otherwise encoded (as by frequency shifting) with information at audio frequency rates, whatever form or mode of transmission or propagation is used.
  • conductive connections such as twisted pairs, telephone lines, etc.
  • transmission line components such as coaxial cable and waveguide, etc.
  • the invention is especially useful for use with signals transmitted by telephone systems which have an assemblage of telephone stations, lines, channels, and switching arrangements for their interconnection, together with all of the accessories for providing telephone communication.
  • audio frequency signals are transmitted by a telephone line consisting of the conductors and circuit apparatus associated with the particular communication channel and consisting usually of a conductor pair between telephone stations and/or between such stations and a central office or offices.
  • a telephone channel suitable for the transmission of telephone signals may not merely consist of conductors but comprises frequently also various other transmission media, including radio frequency links in general.
  • 20 designates an audio facility such as a telephone transmitter and/or telephone receiver such as may constitute a telephone set, i.e., .Instrument commercial, domestic or governmental use.
  • Facility or i__strume receives unprocessed audio signals as an input, such as provided by a microphone of the telephone transmitter.
  • audio frequency signals provided as an input may be those supplied by any of myriad possible sources, such as the output of a conventional microphone, pre-amplifier, tape recorder, output of a modulation system or of a receiver, etc.
  • These signals may consist of tone pulses, frequency shift keying pulses, tone encoded information, teletype signals (TTY) , facsimile date, date signals, and various voice transmissions, data transmissions, etc.
  • any audio waveform that deviates from a true sine wave can be said to' be constructed of related harmonics.
  • a system of the invention provides modification of these harmonics.
  • Audio facility 20 also provides an output for audio signals which have been processed in accordance with the invention, these signals being derived from those received by the system and transmitted through the system to the system of said audio facility. These signals are of the same character however processed by circuitry of the invention, which are provided as an input to audio facility 20.
  • Audio facility 20 is interconnected with interface and switching circuitry 30.
  • circuitry 30 is more fully developed hereinbelow but it is observed at the outset that circuitry 30 is connected to, and provides interfacing with, a telephone or other communication transmission line 40.
  • Transmission line 40 may be a line consisting of one or more conductors, or waveguide, fiber optics, cable, and any of various other transmission line components, including those associated with microwave trans ⁇ mission, which are utilized for the transmission of communic ⁇ ation signals, including data, over one or more channels.
  • modem 50 representative of any of various types of modulators and/or demodulators which may be utilized for either modulating signals, in- eluding radio frequency signals, with the audio input provided to audio facility 20 to be transmitted via trans ⁇ mission line 40, or for demodulating incoming audio frequency signals to be provided, as processed audio output, from audio facility 20.
  • modem 50 may represent circuitry for recovering data received over transmission line 40 and for suitably modulating a carrier with encoded data provided as an input to audio facility 20 for trans ⁇ mission by means of transmission line 40.
  • VOX voice operated switching system
  • VOX 60 is operative to cause circuitry 30 to enable the system for providing processing of the signals to be transmitted over transmission line 40.
  • circuitry 30 Also shown interconnected with circuitry 30 are audio frequency amplifiers 70 and 80 for respectively amplifying audio signals provided to audio frequency 20 for trans ⁇ mission and for amplifying incoming signals to be provided by audio facility 20 as an output.
  • Designated at 90 is a monitor circuit to provide isolation for monitoring signals before they are processed by processing circuitry designated generally 100 in accordance with the invention.
  • Circuitry 30 operates to provide routing of unprocessed audio signals from audio facility 20 for routing through processing circuitry 100 when the signals are to be provided for transmission over transmission line 40. Similarly, incoming signals received from the transmission line are routed by circuitry 30 through the processing circuitry 100 to be provided by"audio facility 20 as processed audio output.
  • VOX circuit 60 causes the interface and switching circuitry 30 to route the signals through processing circuitry 100 in accordance with whether they are incoming or outgoing with respect to transmission line 40.
  • Audio facility 20 which may be a telephone set, including a telephone transmitter 20a and telephone receiver 20b, provide or receives signals from a relay RLla ⁇ which is interconnected with a counterpart relay RLlb by a bypass line Ll.
  • Relay RLlb is operated with relay RLl under the control of .a switch SW1.
  • Relays RLla_ and RLlb are thus operated by switch SW1 either to route signals to and from audio facility 20 for being transmitted or received by transmission line 40 either via bypass line Ll or through circuitry of the invention.
  • relays RLlji and RLlb route signals through circuitry to be processed by processing circuitry 100 of the " invention.
  • processing circuitry 100 of the " invention assuming that signals are received from transmission line 40, the same are routed by relay RLlb to a further relay ⁇ 2a controlled by a switch SW2.
  • Relays RL2a, RL2b, being under the control of switch SW2 thus, allow selective amplific ⁇ ation of incoming signals but are controllable to permit outgoing signals to be provided through line L2 without amplification.
  • Switch SW2 provides manual override also to permit incoming signals to be received without amplific ⁇ ation if desired.
  • O...PI Switch SWl may be manually operated or automatically operated by the initiation of a telephone connection.
  • relays RLla and RLlb can provide automatic bypass switching that connects the processing circuitry 100 in line after all dialing and line connection has been achieved.
  • Relays RLla_ and RLlb may preferably provide time delayed DC switching action which allows 15 sees, for line dialing and phone line access upon which time the processing circuitry becomes an integral part of the telephone circuit.
  • a dotted line connection of switch SWl with audio facility convention ⁇ ally reflects control over relays RLla_ and RLlb by audio facility 20 for providing the foregoing functions.
  • Relay RL2a is operated by switch SW2 to selectively route the incoming or outgoing signals through a conven- tional audio frequency amplifier 80 or else through a line L2a. without ampli ication, to a corresponding relay RL2b operated with relay RL2a and also under the control of switch SW2.
  • Relay RL2b routes the incoming signals to an impedance matching transformer TI through a line L2b.
  • Outgoing signals are routed to relay RL2 ⁇ , for amplification, by a line L2o from transformer TI.
  • the latter provides impedance matching of the 600 ohm impedance, for example, of transmission line 40 to a higher impedance of nominally 50,000 ohms associated with circuitry 100.
  • 50 ohm or 300 ohm transmission lines may be used for trans ⁇ mission.
  • transformer Tl and other impedance matching transformers T2 and T3 are selected (or may have appropriate windings) for the desired impedance match.
  • Transformer Tl supplies the incoming signals to a further relay 3a ⁇ which, with a corresponding relay RL3b, is under the control of a manner switch SW3.
  • Relay RL3a delivers the incoming signals via line L3 to replay RL3b and thence, via lines L4 and L5 to the input of processing circuitry 100 of the invention. Signals are processed in accordance with the operation of the processing circuitry 100 discussed hereinbelow, being provided upon an output line L6 which also is interconnected with relay RL3a..
  • the latter routes signals provided upon output line L6 through a further line L7 to a further impedance matching transformer T2, which again provides a match between the 50,000 ohm impedance of circuitry 100 and the 600 ohm impedance associate with telephone lines.
  • Transformer T2 provides the processed signals by a line L8a_ to a relay RL4ci which, with a corres ⁇ ponding relay RL4b, both being operated by a switch SW4, permits signals to be amplified by an audio frequency amplifie 70 or else provided directly over a line L8b.
  • a line L9 between relay RL4a and relay RLlai routes the processed received signals to audio facility 20 for being reproduced by telephone receiver 20b_.
  • the route taken by audio signals picked up by telephone receiver 20a demonstrates still other features of the circuitry.
  • the user at a local facility providing an audio signal to transmitter 20a_ has the result of producing signals by means of audio facility 20 which are delivered to relay RLlci for being routed through line L9 to relay RL4a_.
  • relays RL4a and RL4b permit audio frequency amplifier 70 to amplify these signals so that they are of a level adequate for being pro ⁇ Roud by circuitry 100. Or, if they are already of high level, they may be provided directed by line L8 to relay RL4b.
  • signals re- ceived by RL4]b are made available by a line L8£ to a further impedance matching transformer T3, which again may provide matching between the 600 ohm line impedance and the 50,000 ohm impedance of circuitry 100.
  • the high impedance secondary of transformer T3 provides the output signals to the VOX circuit 60.
  • the latter controls a relay RL4 to provide a bypass route for signals if the VOX circuit 60 senses the presence of audio signals being delivered by the secondary of transformer T3.
  • Circuit 60 is of an entirely conven ⁇ tional nature such as will be understood by those skilled in the design of audio circuitry and is configured for _ ⁇ - ⁇ f _f controlling the operation of relays RL3a and RL3b. Wheft o...? thus indicating that telephone transmitter 20a_ is the predominant source of signals, relays RL3a and RL3b are switched to provide routing of signals as follows:
  • Relay RL3b supplied signals from bypass relay RL4 via line L4 to the input, via line L5 of processing circuitry 100.
  • line L6 providing the processed audio output signals, is connected with relay RL3a and the latter then routes signals to transformer Tl and, thence, via relays RL2a, RL21D, to relay RLlls for being delivered upon transmission line 40.
  • a line L10 which provides for the delivery of signals, prior to processing, to an RF amplifier 90a, the operation of which is controlled by a switch SW5.
  • amplifier 90a provides high- level output via a line Lll for permitting test monitoring, recording, etc. of signals prior to being processed through circuitry 100.
  • Indicated at 50a_, 50b and 5 ⁇ £ are three modulator- demodulator circuits (so-called modems) . These have respective outputs Ll2a, Ll2b and L12£ for receiving unmodulated RF inputs of AM, FM or SSB character.
  • modulator-demodulators have respective outputs Ll3a_, L13b and L13£ for providing modulated outputs of AM, FM or SSB type, respectively, for delivery via transmission line, microwave, etc.
  • Signals which are received by any of circuits 50a, 50b_ or 5 ⁇ £ and which are demodulated are made available for processing in accordance with the invention.
  • switches SW6a, SW6b and SW6£ which are each interconnected with the respective modulator- demodulator circuit 50a, 50b or 5 ⁇ £ and also with the input line L5 of processing circuitry 100 and its output line L6. Accordingly, the demodulated signals are provided to processing circuitry 100 to be processed before being redelivered via the respective switches to the corresponding modulator-demodulator for modulation of the appropriate RF output thereof.
  • the circuitry of the invention may be used for the processing of audio frequency signals no matter whether they are transmitted via telephone or other transmission line or via radio.
  • the system demonstrated in FIGURE 2 is described as having various relays, preferably the system is constructed utilizing electronic switching devices or solid state relays in lieu of mechanical relays. Therefore, a system of the invention can be constructed using conventional state-of-art logic circuitry, including microprocessors and the like, for. control of switching and other operational functions. Further understanding of the system will be had by considering the various features of the circuitry shown in block diagrammatic form in FIGURE 1 and in greater detail in FIGURE 2. Because an understanding of the audio processing provided by the system of the invention is critical to an understanding of the configuration and operation of the system in its entirety, the audio processing, circuitry 100 is first described.
  • An auxiliary output 117 is provided for presenting output signals at high levels such as for driving various recording devices, e.g., oscilloscopes, spectrum analyzers, and the like, without limitation.
  • signals to be processed before, or after, transmission over a line system may most typically be constituted of audio frequency information containing voice content or speech
  • tones and tonal data of various types of an audio frequency may be processed advantageously by processing circuitry 100, such as to improve signal- to-noise ratio (S/N) and/or achieve other objects of the invention.
  • audio processing circuitry 100 is utilized for transferring audio frequency signals before or after live transmision in such a way that the efficiency of transfer is maximized or optimized by processing the signals for various purposes such as, for example, to provide high average modulation power, to enhance signal intelligibility, to provide high clarity fo signal " transmission, and to avoid loss of audio dynamics, among numerous other objects hereinabove stated.
  • Input 113 delivers audio signals to a bandpass input filter 119 for providing filtering of frequencies to achieve a pass band of between 300 Hz and 3 kHz. Filter 119 effectively limits all other frequencies.
  • the pass band thus achieved is merely that preferred and utilized to ' advantage in the operation of the present system and may be varied in accordance with the purpose intended for the present system, e.g., in having different widths and different lower and upper frequency limits.
  • a switch SW7 connected by a circuit lead 120 between input 113 and the output 121 of filter 118 permits selective disablement of filter 119 for purposes stated hereinbelow.
  • the output of the bandpass input filter 119 is delivered by output connection 121 to a primary active frequency control 123.
  • Control 123 effectively splits the audio spectrum of the signals delivered to it into two separate frequency bands.
  • the lower band is from 250 Hz to 1.2 kHz and the upper frequency band is from 1.4 kHz to 3.5 kHz ' .
  • Control 123 includes means for selectively controlling the amplitude of the audio content of each of these audio bands allowing the user either to attenuate or to provide gain in each of said bands over a preferable range of + 10 db.
  • the primary active frequency control 123 preferably incorporates an input gain control for purposes later appearing.
  • the control components of circuit 123 also allowing individual tailoring of -out-of-band harmonics which are reconstituted by processing of audio signals by circuitry 100 of the system.
  • Signals from control 123 are then provided by a connection 125 to a primary voltage compressor 127.
  • the latter provides a relatively high compression range, i.e., preferably 135 db, as well as pre-emphasis of high frequency audio components to compensate for high frequency losses which otherwise could occur during processing.
  • Compressor 127 is preferably selected to limit all audio dynamics to a 27 db window with a tracking error of not greater than about +_ 3 db.
  • Included within compressor 127 is a variable gain cell which is indirectly controlled, via a lead 128, by an automatic gain control (AGC) circuit 129 described hereinbelow.
  • AGC automatic gain control
  • Also connected with compressor 127 by a lead 130 is an LED drive circuit 131 for driving an LED indicator 133 in accordance with the operation of compressor 127 to provide the system operator with an indication of the extent to which maximum useable compression is being provided by compressor 127.
  • the output of compressor 127 is delivered to ' a secondary active frequency control 135.
  • This circuitry is adapted to split the now dynamically compressed audio signals into two frequency bands; there being a lower frequency band of preferably from about 300 Hz to 1.5 kHz and the upper frequency band of preferably from about 1.5 kHz to 3 kHz.
  • Control 135 is adapted for providing gain and attenuation control within these two frequency bands variable over a range of preferably + 12 db.
  • manual con ⁇ trol means are provided for the user to selectively deter ⁇ mine the gain or attenuation within each frequency band.
  • control 135 is adapted for providing gain peaking and attenuation occurring about center frequencies with the respective lower and upper bands at preferably 1 kHz and 2.4 kHz. This feature allows control 135 to selectively disregard inter ⁇ acting, and possibly distortion-productive audio harmonics occurring within the input pass band established by input filter 119.
  • the frequency controls within control circuit 135 may be set to provide neither attenuation nor gain so that not only would no gain or attenuation but also no distortion will be provided for the signal passing through control 135.
  • the output of frequency control 135 is fed to a secondary dynamic compressor 137 providing an extremely fast tracking system with extremely low tracking distortion (preferably less than about 0.1%) and accepting and providing compression of signals with a dynamic amplitude range of up to about 120 db while achieving a compression window of preferably only 50 db, yet providing a third harmonic distortion (THD) figure of less than preferably 1%.
  • AGC circuit 129 is interconnected with circuit components of compressor 137 by a connection 140 to provide an input for AGC 129 which in turn controls primary voltage compressor 127 by circuit connection 128, thereby providing a negative AGC feedback loop for limiting the degree of primary voltag compression provided by primary compressor 127 as a ti e- delayed function of compression by secondary compressor 137 all as more fully explained hereinbelow.
  • the connection of AGC circuit 129 to compressor 137 provides to primary compressor 127 a d.c. reference signal derived from compression stages of compressor 137.
  • AGC circuit 129 by interconnection with secondary compressor 137 amplifies a tracking voltage output of the secondary compressor and delivers a voltage varying within preset parameters to a variable gain cell of primary voltage compressor 127 as a function of this tracking voltage. This is carried out for the purpose of achieving extremely high tracking stability and for limitin the third harmonic distortion while reconstituting through voltage gain via the secondary active frequency control 135 of the original audio dynamics fed to secondary dynamic compressor 137. However, reconstituting of otherwise lost audio dynamics occurs as well in other portions of the system circuitry.
  • a meter drive circuit 143 for driving, as indicated at 144 , a meter 145 preferably of a moving coil movement type to provide averaging.
  • the meter serves as a visual indicator for displaying not only the compressed output voltage provided by secondary dynamic compressor 137 but also average peak dynamic compression, and thus indicates the extent to which the overall capability of the audio processing circuitry 100 is being utilized.
  • an LED drive circuit 149 for driving an LED indicator 150 to indicate the degree of compression being achieved by secondary dynamic compressor 127.
  • the output of compressor 137 is delivered to a bandpass output filter 152 for providing sharply attenuated filtering of the now processed audio signals within a preferable pass band of between 300 Hz and 3 kHz with very sharp roll-off or corners at the edges of the pass band to limit the processed audio between these upper and lower limits.
  • Filter 152 preferably provides unity gain and has an extremely low noise figure so as to avoid introducing further noise into the now processed audio. If desired, the filtered audio signals presented at output 115 may be attenuated to provide signal levels suitable for other systems being driven by the present system.
  • filter 152 Also interconnected in a circuit 153 around filter 152 is a switch SW8 for selectively disabling the operation of filter 152 for purposes noted hereinbelow.
  • the output of filter 152 is also provided, as indicated at 155, to an audio amplifier 156 constituting a high level output stage and providing the high level output 117 noted pre ⁇ viously.
  • the circuitry of bandpass input filter 119 is seen to comprise circuit elements providing cascaded high and low frequency seasons.
  • An operational amplifier OA1 has its non-inverting input interconnected with input terminal 113 through a pair of capacitors Cl, C2 and biased to ground through a resistor Rl. Feedback between the output of the amplifier and said input is provided by a circuit including a capacitor C3 and resistor R2, with capacitor C3 being connected to a node between capacitors Cl and C2 to provide capacitive feedback for tailoring frequency response. This node is also biased to ground through a resistor R3.
  • the non- inverting and inverting inputs are connected to circuit ground through respective capacitors C4, C5.
  • a bypass capacitor C6 conventionally connects a power supply terminal 158 to circuit ground.
  • the output of operational amplifier OAl is series-conne through a capacitor C6 and resistor R4 and a further resisto R5 to the non-inverting input of a further operational amplifier OA2.
  • Capacitive feedback between its output and its non-inverting input is provided by a capacitor C7 for frequency response control with d.c. feedback for gain control being provided by a resistor R6.
  • a resistor R7 and capacitor C8 are connected in parallel between the non-inverting input and circuit ground, the node common to resistors R4, R5, and R6 being ited similarly to ground through a capacitor C9, the inverting input of operational amplifier OA2 is tied directly to ground.
  • the output of operational amplifier OA2 is provided through a capacitor CIO to output lead 121.
  • a conventional bypass capacitor Cll connects operation amplifier-OA2 to the circuit ground.
  • Switch SW7 which is connected by lead 120 between said input terminal 113 and lead 121 is provided so that, when it is closed, the bandpass input filter is effectively rendered inoperative, i.e., taken out of the circuit. This allows selective elimination of the bandpass input filtering under certain possible conditions of use in which it is not desired or not necessary to limit the audio signals being processed to the narrow pass band ordinarily determined by the input filter circuitry 119.
  • Each of the operational amplifiers may be part of a single commercially available integrated circuit . (IC) type such as LM387 exhibiting electrical characteristics and peri ⁇ meters compatible with the node of intended usage of the present system .and requiring power supply voltages (as delivered by terminal 158) of, e.g., + 15 v.d.c.
  • IC integrated circuit .
  • the circuit values such as that of resistor R6 may be varied to control the gain of the bandpass input filter. But preferably filter 119 is configured to provide unity gain.
  • filter 119 provide upper and lower corner frequencies of 2.7 kHz and 300 Hz, respectively, and a roll-off characteristic of -40 db. per decade, as well as very low third harmonic distortion (THD) .
  • Filter 119 providing unity gain, preferably can handle an input signal of between -35 and +10 db. without clipping or distortion.
  • the primary active frequency control 133 similarly utilizes two operational amplifiers OA3, OA4 for control of the amplification of the gain of individual upper and lower frequency bands. Interconnected with each of these operational amplifiers are respective resistive-capacitive circuits 160a_, 160b for establishing, with respective operational amplifiers, individual circuits for providing selective amplification and control of audio frequency components within the respective audio bands.
  • the input signal provided by lead 121 is delivered across a potentiometer R9 having a wiper 159 selectively variable for controlling the overall gain of stage 123.
  • a potentiometer R9 having a wiper 159 selectively variable for controlling the overall gain of stage 123.
  • circuit 160a is described exemplarily.
  • :It comprises a capacitor Cl3a coupling the signal present on wiper 159 through a resistor R10 to a further potentiometer Rlla_ having a wiper 161 which is selectively controllable by the user to serve as a high frequency gain control connected from opposite sides of potentiometer Rll to its wiper are capacitors C14, C15.
  • the signal present on 161 is provided through a resistor R13 and thence through a capacitor C17a to the non-inverting input of operational amplifier OA3, which has its inverting input referenced to ground through a circuit including a resistor R14a_ which is in turn shunted by a series-connected capacitor C18a and resistor R15a.
  • potentiometer Rll is connected through a capacitor C20a and resistor R16 to the circuit ground.
  • a frequency compensating circuit comprising resistors R17a and R18a_ and a capacitor C19a connected across the latter and with one end thereof being connected to circuit ground.
  • circuit 160a_ together with operational amplifier OA3 constitutes an active high frequency control circuit providing gain control over frequencies determined by the setting of potentiometer wiper 161, and with gain in the frequency band being variable over the range of + 12 db. within the frequency range of preferably about 1.5 kHz to 3 kHz.
  • Gain peaking and attenuation peaking occurs oreferably about 2.4 kHz.
  • the output of operational amplifier OA3 is provided through a capacitor C25a_ to output lead 125.
  • circuit 160b_ together with operational amplifier OA4 constitutes an active low frequency control circuit providing gain control frequency over frequencies determined by the setting of a wiper 165 of potentiometer C20a_, and thus determining the level of signals provided to the operational amplifier OA4 through capacitor C17b.
  • the frequency band preferably is from 300 Hz to 1.5 kHz and with gain peaking and attenuation peaking occurring at preferably about 1 kHz.
  • 0?._H are provided from the output of operational amplifier OA4 through a capacitor C25b and thus delivered to output lead 125.
  • operational amplifiers 0A3 and OA4 may both be available as a single integrated circuit (IC) such as of the commercially avail ⁇ able type UA739, thus providing high loop gain without any substantial distortion.
  • IC integrated circuit
  • compressor 127 comprises an integrated circuit IC1 constituting a compiressor expandor or so-called compandor including a full wave rectifier, a variable gain cell and an operational amplifier including a biasing system within it, all as shown in
  • FIGURE 6A Although a general depiction of elements thereof is represented by FIGURE 6A, no specific description is necessary in view of the fact that circuit ICl may be of commercially available form such as that designated NE570/571 But it is noted that there is an internal summing node within the operational amplifier (not shown) which is biased at a voltage preference, and signals supplied to the inte ⁇ grated circuit are averaged by circuitry interconnected therewith, as shown in FIGURE 6. The averaged value of the input signal establishes the gain of the variable gain cell (see FIGURE 6A) which is, accordingly, proportional to the average variance of the input signal capacitively coupled thereto. In any event, the operation of such circuitry is described and will be understood by reference to the above-noted pending ⁇ . S. Application Serial No. 59,394 of Graham P. Bloy, entitled “Complete Audio Pro ⁇ cessing System", filed July 20, 1979.
  • gain cell of compandor circuit ICl function as an expandor, by providing negative feedback to the operational amplifier therein, compression is realized.
  • C-. ⁇ compressor 127 For present purposes, it is sufficient to observe that ICl is interconnected as shown by pinout numerals, with the following resistive and capacitive circuit components which may have the nominal values indicated:
  • lead 128 interconnected with the gain cell of the compandor circuit ICl is lead 128 which provides a feedback signal of a limiting character from the automatic gain control, circuit 129 as a function of the overall gain signalled by gain control circuitry 129.
  • said lead 128 provides said AGC signal to the gain cell of compandor ICl through resistor R26.
  • the overall purpose and function of this negative feedback is discussed below but it is noted pre ⁇ liminarily that the gain cell within circuit ICl is controlle in a negative sense in response to increase in the AGC signal supplied by lead 128, thereby to reduce the amount of primary compression achieved by stage 127 with increasing gain feedback.
  • the feedback is essentially negative or limiting.
  • a terminal for supplying low voltage d.c. potential for operation of circuit ICl is indicated a terminal for supplying low voltage d.c. potential for operation of circuit ICl.
  • the dynamically compressed output signal is provided by capacitor C34 across a load resistor R32 , and is appropriately attenuated by R35 for delivery through a resis.tor by lead 127 to the secondary active frequency control circuitry, shown in FIGURE 7.
  • circuit lead 130 prior to being- coupled through capacitor C34, provides the compressed audio output from stage 127 to LED drive circuit 131, as disclosed in FIGURE 10.
  • circuitry for con- stituting the LED drive 131 and LED 133, as well as the LED drive 149 and LED 150.
  • the LED indicator lamp whether that designated at 133 or that designated at 150, is suitably mounted for being observed by the user, being driven by circuitry including a pair of NPN transistors Ql, Q2.
  • the base of transistor Q2 is driven by a unipolar signal provided through a diode Dl and delivered through a resistor R37.
  • the base of transistor Ql is biased to ground through a resistor R38.
  • Its collector is provided with a supply potential by means of a terminal 171 through a current limiting resistor R39, while a similar resistor R40 provides a supply of voltage to the collector of transistor Ql.
  • the base of the latter is connected through a resistor R41 to the collector of transistor Q2.
  • Coupling is provided between the collector of transistor Ql and the base of transistor Q2 by a series connected capacitor C36 and resistor R42.
  • Control 135 functions to reconstitute harmonic dynamics lost in processing of the signal through primary compressor 127.
  • Control 135 comprises a pair of operational amplifiers OA5, OA6 which are connected to provide high and low pass sections of a Butterworth filter.
  • the operational amplifiers may each be of the commercially available type designated LM349 with both operational amplifiers being part of a single integrated circuit which is adapted for being powered by positive and negative potentials, as at 15 v.d.c, supplied to respective terminal.. 173, 174.
  • Bypass capacitors C38, C39 are connected across these power supply inputs.
  • Each of the operational amplifiers has its inverting input connected to the circuit ground.
  • the input signal is provided by lead 127 through a capacitor C40 and resistor R44 to the non-inverting input of operational amplifier 0A5.
  • a resistor R45 interconnects the output and latter input of the operational amplifier for feedback purposes, the input being biased to ground through a further resistor R46.
  • the output of operational amplifier OA5 is provided through a capacitor C42 to a frequency gain control circuit 175 having two parallel branches providing at one end a node 176 constituting an input of the circuit and an opposite node 177 interconnected with the output lead 136 of frequency control circuitry.
  • a first one of the branches comprises a resistor R47, a potentiometer R48, and further resistor R49, there being capacitors C43, C44 connected between opposite ends of potentiometer R48 and its wiper 178.
  • the wiper is interconnected through a resistor R50 and capacitor C46 to the wiper 178 of another potentiometer R51 forming with resistors R52 and R53 in series with it a second parallel branch of circuit 175.
  • a node 179 between resistor and capacitor C46 is connected to the non-inverting input of operational amplifier OA6, which input is biased to ground through a resistor R54.
  • the secondary active frequency control is designed to provide tailoring of the response curve between 300 Hz and 3 kHz.
  • the low frequency section of the circuitry of frequency control 35 is designed to control response between 250 Hz and 1200 Hz, the high frequency section being designed to control response between 1400 Hz and 3500 Hz.
  • operational amplifier 0A5 acts as a buffer to ensure low driving impedance to the low and high frequency control circuits 175.
  • the input impedance of this stage of the buffer amplifier is about 0.1 megohms.
  • Capacitor C40 and resistor R44 provide d.c. blocking and impedance matching for the input of operational amplifier OA5.
  • Resistor R45 provides a feedback path between the output and the non-inverting input of this operational amplifier.
  • Capacitor C42 provides d.c. blocking of the output of the operational amplifier.
  • High frequency control elements comprise resistors R50, R52, and R53. Potentiometer R51 allows the high frequency section of the filter to be set between preferably 0 and 22 db gain.
  • ⁇ 3S_._ section comprises resistors R47, R49 and potentiometer R48, as well as capacitors C43, C44. Potentiometer R48 allows low frequency control preferably between 0 and 22 db gain.
  • node 179 represents the output of the frequency control circuitry 175, being this supplied to the non-inverting input of operational amplifier 0A6, which acts as the active element within this active frequency control circuitry.
  • a feedback path is provided by the interconnection with node 177 because of the interconnection with resistors R49, R53.
  • Capacitors C40, C42 provide not only d.c. blocking but establish low frequency roll-off' of the circuitry.
  • any integrated operational amplifier substituted have a fast slew rate such as better than 2.5 v. per micro second ... " allowing undistorted full swing performance up to a frequenc of 25 kHz.
  • the total harmonic distortion is preferably kept low being typically not greater than 0.05% [0 dbm
  • resistor R46 ensures stability at unity gain as the integrated circuit operational amplifiers are internally compensated for positive gains of five or greater, in the case of the LM349 integrated circuit.
  • Chosen design specifications are preferably such that the low frequency section of the secondary active filter circuitry has a gain of 22 db with a low frequency lower 3 db corner at 30 Hz and with a high frequency upper 3 db corner at 10 kHz.
  • corner or corner frequency refers to cut-off frequency conventionally representing 3 db insertion loss of the respective circuit.
  • Circuitry for providing regulated potentials suitable for the operational amplifiers fo the secondary active frequency control 135 is illustrated in FIGURE 12.
  • a pair of terminals 181, 182 provide a.c. line voltage across the primary winding 183 of a transformer having its secondary winding 184 connected across a full wave bridge rectifier 185.
  • a first filtering or a.c. decoupling capacitor C48 Connected across the latter is a first filtering or a.c. decoupling capacitor C48. Across this is connected a pair of resistors R56, R57 which in turn each have connected across them capacitors C50, C51 whereby there is provided a floating ground node 186 intermediate these capacitors. Node 186 is connected to the circuit ground.
  • the -potentials on the opposite sides of each of capacitors C50, C51 are provided to respective integrated circuits IC2, IC3, such as each of commercially available type UA7815 integrated circuit regulators. Each such integrated circuit is connected also to the circuit ground and each provides a respective output 187, 188 to provide highly regulated voltages, preferably, +15 v.d.c. and -15 v.d.c.
  • amplifiers OA5, 0A6 of the secondary active frequency control and others with a voltage stability of within + 1%.
  • Similar circuitry may be utilized for developing other supply potentials for operation of other components of this system. Alternatively, battery power supplies may be utilized.
  • input lead 134 provides the signal processed by secondary active frequency control 135 across a resistor R59 and through a coupling capacitor C53.
  • the signals are then provided through a high frequency emphasis network comprising a capacitor C54 and resistor R60 to a resistor R61.
  • Said resistor R61 then couples the input signal directly to the inverting input of operational amplifier OA7.
  • the inverting and non-invertir inputs of the operational amplifier are tied together by a series circuit comprising a capacitor C5.5 and resistor R62.
  • the inputs of operational amplifier 0A7 are inter ⁇ connected with a gain cell 185 and a full-wave rectifier 186, both of which preferably are portions of an integrated circuit compressor expandor i.e., compandor, device such as that commercially available under type designation NE570/571 all as described below.
  • a gain cell 185 and a full-wave rectifier 186 both of which preferably are portions of an integrated circuit compressor expandor i.e., compandor, device such as that commercially available under type designation NE570/571 all as described below.
  • Such a device may also include an internal or self- contained integrated circuit operational amplifier but, in the case of the preferred compandor circuit NE570/571 employed in the present system, the internal operational amplifier is not utilized. Connections are instead made, as indicated in FIGURE 8, to the gain cell 185 and rectifier 186 components of such compandor circuit. Also, there are internal resistive components of compandor device including a resistor R63 which is connected to the output 187 of the gain cell and connected at the opposite end to the circuit ground. A node 188 of the circuit represents the input to the gain cell, there being an internal resistor R64. Gain cell 185 is adapted to be controlled by rectifier 186 in accordance with a capacitor interconnected by a terminal 189 of rectifier 186.
  • rectifier 186 provides full-wave rectification of the audio signal supplied to the input of compressor 137. as reflected at the output of operational amplifier
  • a capacitance expandor circuit 190 comprising operational amplifiers 0A8, OA9 is interconnected with rectifier 186.
  • Circuit 190 includes a capacitor C56 which is interconnected between the output of operational amplifie OA9 and the non-inverting input of operational amplifier OA6, which point is also interconnected with the capacitance input 189 of rectifier 186.
  • the inverting input of of operational amplifier is tied directly to its output, which is coupled by a resistor R65 to the non-inverting input of operational amplifier 0A9, which input is biased to ground through a pair of diodes D2, D3.
  • a load resistor 5 R66 is connected across the output of operational amplifier OA9.
  • resistor R67 which is internal to the integrated circuit device type NE570/571 preferred whereby a terminal or node
  • 10 191 constitutes the input to the rectifier stage.
  • Inter ⁇ connected with node 191 is a parallel combination of a resistor R68 and capacitor C58 which provide high frequency pre-emphasis for the signal provided to the input of the rectifier.
  • Such input is delivered by a capacitor C59 which
  • gain cell 185 2.0 being provided to the gain cell 185 through capacitor C60 and resistor R64.
  • a second feedback path is provided through capacitor C59, the pre-emphasis network noted above, and resistor R67 to rectifier 186.
  • the rectifier controls the gain provided by gain cell 185, which is an integrated
  • Gain cell 185 equivalently functions as an expandor but, since its output 187 is interconnected with the in-
  • circuit 190 operates to expand the
  • a further feedback circuit comprising a pair of resistors R70, R71 is interconnected between the output and inverting input of the operational amplifier, there being a capacitor C62 providing a.c. bypass to circuit ground. Resistors
  • R70, R71 provide d.c. feedback path for operational amplifi 0A7 since there is no d.c. feedback path through gain cell 185.
  • the gain cell is provided with a terminal
  • D.c. shift trim for the gain cell input 188 is provided similarly through a resistor R75 in accordance with the position of wiper 196 of a potentiometer R76 across which a 3.6 volt d.c. potential is supplied.
  • a resistor R75 in accordance with the position of wiper 196 of a potentiometer R76 across which a 3.6 volt d.c. potential is supplied.
  • a pair of back-to-back zener diodes D4, D5 are connected between the output and circuit ground, being selected for threshold potential of, for example, preferably 3 v. to limit the output of the amplifier and preclude it from exceeding predetermined levels. This limits the output swing to avoid overloading any succeeding circuit stage to which the output of the secondary dynamic compressor circuit is supplied, such as otherwise may occur if excessive signals caused by ignition or electrical noise, etc. are present in the signals being processed.
  • the output of the operational amplifier is provided through a capacitor C63 to output lead 148, across which there is a load resistor R77.
  • compressor 137 comprises an operational amplifier (OA7) as well as feedback circuitry interconnecting the output and non-inverting input of this amplifier for providing a nonlinearly increasing negative feedback signal to the input in response to increase in the level of the tonally controlled audio signal on input lead 136. Ignoring the change in attack time or response produced by capacitance expandor circuit 190, the signal gain is:
  • Gcomp m where I. is the current flowing into an effective internal summing node of operational amplifier OA7, V. is the average input voltage of the audio signal input to compresso 137 and K is a gain constant.
  • Gain cell 185 provides an exponential response in gain in response to step changes in amplitude, said exponential response being effected by the time constant resulting from the capacitance represented by circuit 190 at terminal 189 of rectifier 186.
  • family of curves represents typical input-output tracking of compressor 137.
  • the ordinate represents output level and the abscissa represents the input level.
  • operational amplifier OA7 may be of commercially available type TDA1034 and opertional amplifier OA8, 0A9 may each be of commercially available type LM387:
  • operation in accordance with the invention involves reconstituting harmonics typically characteristic of himan speech, among other aspects of operation, which harmonics otherwise would be of inaudible and of essentially ineffective amplitude if the audio signal were not processed in accordance with the invention, owing to constraints imposed by normal compressio or narrow band filtering normally encountered in modulation and RF transmission systems. Accordingly, it is desired that operational amplifier OA7 be of a relatively high quality character, providing typically a high slew rate and capable of providing .transmission of audio frequencies up to at least 15 - 16 kHz.
  • Circuit 190 is a gyrator which effectively increases the capacitance at terminal 189, being the apparent magnitude of capacitor C56, in accordance With decrease in signal level, i.e., the dynamic input of compressor 137.
  • the response time of the compressor becomes considerably longer at low signal levels, since circuit 190 operates effectively to speed up the compressor attack time at such low signal levels. For example, when the rectifier input level drops from 30 dbm to -30 dbm, the time constant
  • Ol.-PI increases from 10.7 C__ ect X 10 3 to 32.6 C rect X 10 3 , where C is the effective capacitance interconnected with rectifier 186. This in turn effects the gain cell response because gain cell 185 is controlled by rectifier 186. This avoids or greatly reduces any mistraking of low signal dynamics.
  • compressor-expandor compactor
  • the compressor is operating at high gain when there is a small input signal, but when a higher level input signal is provided to the circuit lead 134, the circuitry operates to effectively reduce the gain.
  • Over ⁇ loading is, however, precluded even in the case of a large signal supplied to input 134 (as for example, ignition noise) because of the clamping action of diodes D3, D4, D5.
  • capacitor C54 and resistor R60 as well as capacitor C58 and resistor R68 provide high frequency pre-emphasis by altering com ⁇ pression gain accordingly.
  • wiper 194 of potentiometer R74 is adjusted for proper THD trim by utilizing a 0 db signal at 10 kHz input audio in ⁇ put signal to the system and will be referenced by meter 145. Also the d.c. trim potentiometer R77 may have its wiper 196 adjusted to provide minimum envelope bounce when inserted tone bursts are applied to the input of the system.
  • the secondary dynamic compressor circuitry will provide up to 135 db of dynamic compression for a 0 db input signal.
  • the automatic gain control (AGC) circuit 129 is shown.
  • Lead 141 provides an input for the audio frequency signals processed by the secondary dynamic compressor 137 whose output effectively provides a tracking voltage provided by feedback circuit to the d.c. rectification stage, i.e., rectifier 186 and expandor circuit 190, of the secondary compressor 187, while serving also to deliver the -processed audio signals to bandpass output filter 152.
  • This AGC input is supplied to a diode D6 for rectification and thence to the gate of a field effect transistor (FET) 199.
  • FET field effect transistor
  • a time constant delay circuit for providing a delayed action of the AGC circuitry and comprising a capacitor C65 in parallel with a resistor R80, both connected at one end to the circuit ground, and a capacitor C66 having one end connected to the drain electrode of the FET.
  • the FET effectively isolates the input by its high impedance, being adapted by change in its conductivity to change the level of a signal applied to the non-inverting input of an operational amplifier OA10, which input is biased to ground through a resistor R81 and interconnected to the output of the operational amplifier for feedback purposes through a resistor R82 thereby to establish control over the gain of the latter.
  • the inverting input is biased to ground through a resistor and is connected through a resistor R84 and potentiometer R85 having its opposite end and a wiper 201 tied to a lead 202 which is supplied by a terminal 203 ' with positive voltage, i.e., 12 v.d.c, whereby the gain of the operational amplifier may be controlled by the.setting of wiper 201.
  • a bypass capacitor C68 couples to ground any AC component present on lead 202.
  • Lead 202 is shown interconnected with the lead 203 for supplying the operational amplifier with its operating voltage.
  • a circuit Connected between 202 and the output 204 of the operational amplifier is a circuit comprising a pair of potentiometers R86, R87 and meter 145, which is preferably of the moving coil type.
  • the output 204 is tied directly to lead 128 for providing an AGC feedback connection to the primary voltage compressor 127.
  • One side of the meter 145 is connected to ground through resistor R88. Wipers
  • potentiometers R86, R87 provide calibration of the meter.
  • the meter indicates the overall signal compression gain level and thus displays an indication of the extent to which the system is being utilized to capacity.
  • the meter is of the moving coil .type, providing averaging of the instantaneous variations in the output' of operational amplifier OA10 to avoid wildly fluctuating changes in the indicated output which would be difficult to observe.
  • wiper 201 is adjusted to permit variation in the level of voltage provided to the inverting input of the operational amplifier within a normal swing or variation in the potential at output 204 of from about +2 to about +9 v.d.c, which potentials are of the proper magnitude for the primary voltage compressor 127.
  • digital signals of the type involved in data transfer might require such rapid reaction.
  • narrow bandwidths are involved so that one need not provide capacity for handling harmonics normally present in speech or other audio.
  • the amount of delay which results in the AGC delay path is preselected in accordance with applications of the system and the type and character of signals to be processed. Variation of the AGC time constant are provided by capacitor C65 and resistor R80 which may be varied, as by selection of different components. Of course, conventional multiple switches may be used to permit capacitances and resistances of various values to be substituted for capacitor C65 and resistor R80. Examples of the AGC delay which may be provided by capacitor C65 and R80 are from 0.010 seconds to 3 seconds, as a broadly preferred range, whereas typically a delay of 0.3 - 0.5 seconds may be adequate for various types of audio signals.
  • the delay is to be shorted, i.e., for faster response for transmission of signals of the date character and slower such as 0.3 - 0.5 seconds or even longer for signals of audio or voice character.
  • the amount of AGC feedback can be established in direct relevance to the amount of out-of-band harmonics expected to be present in the signals being transmitted.
  • an LED device circuit 149 and LED 150 of the circuit configuration sh ⁇ wn.-.in FIGURE 10 is also connected to the output 148 of secondary dynamic compressor 137 thereby to indicate the amount of compression attained by compressor 137.
  • the LED 150 is utilized to signal an overload condition resulting from excessive compression.
  • the control of the system may be adjusted to provide operation under conditions such that peak- compression can be handled, as indicated by elimination of LED 150 during processing of audio signals, the controls being adjusted to prevent LED 150 from normally remaining illuminated.
  • the output of the secondary dynamic compressor 148, as thus monitored, is provided to bandpass " output filter 152, the circuitry of which is shown in FIGURE 9.
  • OMPI receives thus processed audio frequency signals through a pair of capacitors C70, C71.
  • the non-inverting input to which the signal is supplied is also biased to ground through capacitor C72.
  • a node 108 between capacitors C70, C71 is biased to ground through a resistor R89 and also is provided through a capacitor C73 with a feedback signal provided by the output of the operational amplifier.
  • a further feedback path is provided through a resistor R90 directly to the non-inverting input, which is biased to ground through a resistor R91.
  • the inverting input is connected to circuit ground through capacitor C74.
  • a terminal 209 is provided for providing d.c.
  • operational amplifier OAll as well as a further operational amplifier OA12, the two being both preferably part of the same integrated circuit such as that commercially available under type LM387.
  • the power supply terminals connected to ground through a conventional by ⁇ pass capacitor C74.
  • the output of operational amplifier OAll is coupled through a capacitor C75 and resistors R92, R93 to the non-inverting input of an operational amplifier OA12.
  • the latter input is biased to ground through a resistor R94 and also through a capacitor C76.
  • Feedback for operational amplifier OA12 is provided first by resistor R95 which is connected between the output and a node 210 between resistors R92, R93. This node is coupled to ground through a capacitor C77. Feedback is also provided directly to the non-inverting input through a capacitor C78.
  • the inverting input of operational amplifier OA12 is connected to ground through a capacitor C80.
  • the output of operationa amplifier OA12 constitutes the output of the bandpass output filter.
  • bandpass output filter having high frequency and low frequency sections and preferably providing low frequency gain of 22 db with the low frequency upper 3 db corner at 30 Hz and with the high frequency upper 3 db corner at 10 kHz. It is • emphasized that bandpass output filter 152 is adapted for providing a considerably greater pass band than that of bandpass input filter 119. Selection of component values to achieve these corner frequencies and pass band characteristics as described above will be apparent to those skilled in the art.
  • a switch SW8 is connected n a lead 153 which extends from the input 148 to the output 115 of the bandpass output filter and, when closed, switch SW8 thus directly connects the input to the output for bypassing the bandpass filter, just as input bandpass may be desired for testing or specialized purposes of the invention, or when processing narrow band signals which do not require filtering before or after processing.
  • Lead 155 supplies the output of bandpass output filter 152 to the high level output stage 156, which is shown in FIGURE 13. Referring to FIGURE 13, lead 155 provides the processed audio frequency signal through a coupling capacitor C81 to the input terminal of an integrated circuit amplifier IC4 is interconnected with the following components having nominal values as indicated:
  • a terminal 211 is provided for supplying operating voltage, e.g., 12 v.d.c, through resistor R99 for powering the integrated circuit IC4.
  • Amplifier circuit 156 operates in effect to provide a buffering of the output 115 and for providing high level, e.g., with 40 db gain, useful for driving various auxiliary apparatus, such as oscilloscopes, monitor displays, frequency counters, spectrum analyzers, and the like.
  • Audio amplifier 70 provides relatively low level amplification to provide adequate signal levels for audio processing and to ensure that processed signals are provided to instrument 20 at levels typical of telephone systems.
  • FIGURE 15 is plot of the voltage gain of circuitry of audio amplifier 70 as a function of frequency showing two different representation gain curves, and thus serving to illustrate the frequency response of audio amplifier 70.
  • Audio amplifier 80 similarly exhibits broad frequency response. It has a capability of delivering substantial power gain, e.g., several watts to enable the system to ' present to transmission line 40 a signal of level adequate for telephone transmission over a balanced 600 ohm line pair, e.g., to present a zero db 0.775 vrms signal even at low levels of input.
  • Voice-Operated Switching e.g., several watts to enable the system to ' present to transmission line 40 a signal of level adequate for telephone transmission over a balanced 600 ohm line pair, e.g., to present a zero db 0.775 vrms signal even at low levels of input.
  • VOX circuit 60 may take any of various forms which are within the design skill of ordinarily skilled circuit designers or may be of a circuit arrangement known in the art, it being required that such circuit procude switching action upon the initiation and continuation of voice signal input to instrument 20.
  • a speech-compression preamplifier realization of a commercially available type LS370 integrated circuit differential operational amplifier may provide a voltage output for electronic switching of the system from a receiving to a transmitting mode.
  • Such circuitry includes an audio output of the operational amplifier which is gain controlled to provide a level for proper audio pro ⁇ cessing and for proper modulation. Modulation-Demodulation
  • AM modulator-demodulator 50a is preferably of conventional design such as known within the art, employing a peak detector for demodulation of the audio from conventional IF signals, e.g., at 455 kHz, as may result from down-conversion of VHF AM signals.
  • FM modulator-demodulator 50b may preferably be a narrow band type employing a quadrature demodulator in a balanced-mixer circuit of conventional design useful for limiting bandwidth operation to + 5 kHz duration.
  • a balanced mixer may be used as a productor detector.
  • a carrier generator may be part of the system for supplying RF signals to the modulator portions ' of circuits 50a_, 50b, 50c
  • Input and output ports permit the coupling of signals to and from lines L12 ⁇ JL - L12£ and Ll3a_ - Ll3£ for interconnection with coaxial transmission lines.
  • Commercially available integrated circuit devices of type families LM273 and LM274 may be employed for the realization of AM, FM, SSB, CW detection circuit associated with the modulation-demodulation portions of the system as described above.
  • the circuit blocks may individually or in combination be assembled on printed circuit boards (PCB r s) of standard size, if desired, and may be assembled in cabinetry.
  • PCB r s printed circuit boards
  • the various modules and blocks of FIGURES 2 and 3 may be provided separately or in a combination of PCB's of the type having an arrangement of contacts along an edge for being mated to a so-called "mother" board or main frame.
  • a system of the invention constructed as hereinabove described, and generally as shown in FIGURE 1, is connected to provide a processing and transmitting facility A having an audio transmitting facility a, audio processing circuitry b and an appropriate terminal facility c
  • the latter may be part of a telephone system, or part of an RF trans ⁇ mitting system.
  • Facility A is shown representatively connected by a communication transmission line (which may or may not include an RF link or links) to a corresponding processing and receiving facility B having a receiving terminal facility £' , audio processing circuitry b and an audio receiving facility ⁇ i 1 .
  • identical audio processing circuitry is used in both facilities A and B.
  • Simplex transmission of signals occurs, and both the transmitted and received audio signals are preferably processed in accordance with the invention.
  • audio processing according to the invention may,.under some circumstances, not be able to be provided at both ends of such a simplex transmission system, even though otherwise desirable.
  • FIGURE 17 illustrates use of systems employing the invention for duplex transmission.
  • a processing and transmitting facility A and processing and receiving facility B are a processing and transmitting facility A and processing and receiving facility B.
  • Corresponding facilities A 1 and B* at the opposite end permit simultaneous two-way communications.
  • the facilities are constructed as in FIGURE 16 and specifically as previously described.
  • the system shown in FIGURE 3 is connected as a part of the system where it is desired to utilize the system for processing audio signals provided by an audio source.
  • the source may be at either end of the line transmission link.
  • the source may be the intermediate amplification stage of a modulation system providing an audio signal to modulate a line signal such as AM, FM, SSB, etc.
  • the system may be utilized for improving intelligibility and clarity of such audio signals utilized for modulation thereby to improve the character of the line transmitted information even though such may be in a relatively narrow band, such as 3 kHz or less or the source may be the intermediate amplification stage of a line transmission receiver which amplifies a demodulated audio signal, which similarly may be of a very limited bandwidth as received, so as to retrieve from the received modulated audio signals clarity and intelligibility and general characteristics of normal human voice or other tonal signals.
  • the system enhances the character of the signals transmitted or received to achieve the various objects of the in ⁇ vention.
  • the two audio pro ⁇ cessing facilities of the invention effectively multiply the phenomena produced by a single processing facility on either end of such a link.
  • the system in effect provides what is most closely analogous to a compressor-expandor phenomena in view of the fact that the system as thus utilized to process both the transmitted and received audio information adds substantial dynamic range as well as improves the signal to noise (S/N) ratio. But in the strict sense, the system is not merely a compressor-expandor (compandor)
  • a compandor is a combination of a compressor at one point in a communication path for reducing the amplitude range of signals followed by an expandor at another point for complementary increase in the amplitude range for increasing S/N ratio.
  • the new system provides overall performance which goes well beyond that of a compandor in a customary sense since it not only improves S/N ratios but also reconstitutes lost harmonics and improves clarity, intelligibility and generally enhances the character of signals processed therethrough.
  • the usually audible characteristics of human speech involving various harmonics particularly of the higher order which give life-like, normal character as well as richness and quality to human speech are typically so suppressed or reduced in magnitude in narrow band transmission as to deprive the received voice signals of character and intelligibility.
  • the processing of audio signals by the invention involves effective reconstitution of these various harmonically related attributes of speech so that the processed audio has a richness characterized by the presence of out-of-band harmonics which have been returned to the processed audio, producing normal life-like intelligibility of the audio signal, particularly speech.
  • the user can be provided with ready panel-front access to gain control potentiometer R9 for variation of the wiper 159 thereof to control the level of signals provided to the primary active frequency control circuit 123.
  • the user can be provided with controls for varying the position of potentiometer wipers 161 and 165 to preselect the amount of gain within the low and high frequency portions of primary active frequency control 123 in accordance with the type of signal to be processed.
  • the wipers for tone control potentiometer R48, R51 can be controllable by the user to preselect the response of secondary active frequency control circuit 135.
  • Front panel accessibility can further be provided for controlling the wiper of potentiometer of R61 to allow selective response not only of the overall gain provided by the secondary dynamic compressor operational amplifier 0A7 but also for controlling THD during operation of the secondary dynamic compressor 137.
  • switches SW7, SW8 are also located for operator usage to permit selective use of the bandpass input and output filters 119, 152.
  • meter 145 is located for being observable by the user.
  • the circuit values of the"LED drive circuits 131, 149 are each chosen to provide for energization of the respective LED 133, 150 when the output of the compressor 127, 137 respectively interconnected with each drive circuit is providing maximum compression.
  • the operator may provide adjustment of primary active frequency control gain potentiometer R9 to allow the output of the primary voltage compressor 127 to reach its full maximum value, as indicated by
  • LED 133 This LED will remain unlit when primary compressor 127 is operating at less than full compression. The user may thus appropriately adjust the overall system gain to allow normal operation to proceed so that LED 133 would only light upon maximum peak magnitude of signals being processed. Similarly, potentiometer wiper 184 of the secondary dynamic com ⁇ pressor 137 is adjusted so that LED 150 normally will remain unlit but will flash momentarily only at maximum peak signal levels.
  • meter 145 The user is continuously provided by meter 145 with an indication of the extent to which the system is operating to the extent of its capabilities thus dis ⁇ playing the overall performance of the system.
  • its indication when speech signals are being processed by the system is such as to give a visual indication of the averaged output voltage of secondary compressor 137, but at the same time the meter will indicate fluxation in dynamic audio content. This indication is particularly useful when speech is being processed through the system.
  • meter 145 produces only an average reading from any given dynamic fluxation pattern, since dynamic voltage peaks will appear far too fast to be tracked by the moving coil type of movement of meter 145.
  • the indication provided by LED 150 is such that any rapid increase in signal which may be in excess of the maximum compression utilizable will be instantaneously displayed by flashing of the LED.
  • audio processing phenomena of the invention would be far better realized on an antiquated system than with a modern telephone system because the dynamic increase in intelligibility and sustinction of speech will be far more noticeable on these aforesaid systems as no type of processing is normally applied.
  • digitized information can be passed over a standard narrow band telephone line to an extent previously regarded as either impractical or impossible.
  • Such information may typically be high speed data such as characteristic of computer links. With the bandwidth available, this information can be sent at higher rates than previously practical.
  • Other applications include mixed communications wherein voice characteriz- ation as well as quality are required, such as live broadcast reporting where distinction as well as good definition in voice character are required.
  • the new system can be utilized for both radio transmission and landline trans ⁇ mission to achieve extremely high levels of intelligibility. Frequencies of Signals Processed and Terminology
  • a system of the invention is primarily intended to provide processing of any of various signals transmitted by line systems (which may, as noted, include RF links) wherein the intelligence is conveyed by voice or data at.frequencies corresponding to a normally audible sound wave, and typically within the audible spectrum of 15-20,000 Hz
  • the terms "audio frequency” or "audio signals” have been employed.
  • principles of the invention may be employed in the design and operation of circuitry for processing signals greater than 20,000 Hz, including those of frequencies or bit rates typically regarded as radio frequencies. Therefore, such terms as “audio frequency signals", etc, are not to be construed as limiting.

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  • Engineering & Computer Science (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Signal Processing (AREA)
  • Reduction Or Emphasis Of Bandwidth Of Signals (AREA)

Abstract

Un système de transfert et de traitement de signaux utilisé avec une ligne de transmission comprend un circuit d'interface de lignes de transmission (A) et un circuit de traitement de signaux (100). Le circuit de traitement possède une entrée (113) de réception d'un signal à traiter, et une sortie de signaux (117) pour fournir un signal traité prêt à une utilisation ultérieure. Un filtre d'entrée de bandes passantes (119, SW7) filtre le signal à traiter pour limiter sélectivement sa largeur de bande. Une première commande de fréquence (123) commande sélectivement le niveau relatif du signal obtenu à partir de ces premiers moyens de filtre de la bande passante (123) pour commander sélectivement le niveau relatif de la dynamique des signaux dans une pluralité de bandes de fréquence différentes pour fournir ainsi un signal commandé en fréquence. Un premier circuit de commande dynamique (127) comprime dynamiquement le signal commandé en fréquence pour produire un signal premièrement comprimé. Une seconde commande de fréquence active (135) commande sélectivement le niveau relatif du signal premièrement comprimé dans une pluralité de bandes de fréquences différentes pour produire un signal premièrement comprimé commandé en fréquence. Un second circuit de commande dynamique (137) comprime dynamiquement le signal mentionné en dernier, fournissant un signal comprimé deuxièmement. Un circuit de réaction (128, 129, 140) interconnecté entre le premier et le second circuits de commande dynamique limite la compression dynamique par le premier circuit de commande dynamique sous la forme d'une fonction temporisée d'augmentation du niveau du signal deuxièmement comprimé. Un filtre de bandes passantes de sortie (152, SW8) filtre le signal deuxièmement comprimé pour limiter sélectivement sa largeur de bande. Le circuit d'interface comprend des circuits de commutation (30) pour l'interconnexion de l'entrée du signal et de la sortie du signal du circuit de traitement de signaux avec la ligne de transmission.
PCT/US1981/001147 1981-08-26 1981-08-26 Systeme de transfert de signaux modules avec un rendement maximum en utilisant des systemes de lignes WO1983000787A1 (fr)

Priority Applications (6)

Application Number Priority Date Filing Date Title
GB08310309A GB2118408B (en) 1981-08-26 1981-08-26 System for maximum efficiency transfer of modulated signals utilizing line systems
JP81503040A JPS59500297A (ja) 1981-08-26 1981-08-26 線路方式を用いた変調信号の転送を最大効率で行なわせるためのシステム
PCT/US1981/001147 WO1983000787A1 (fr) 1981-08-26 1981-08-26 Systeme de transfert de signaux modules avec un rendement maximum en utilisant des systemes de lignes
DE19813152946 DE3152946T1 (de) 1981-08-26 1981-08-26 System zur uebertragung von modulierten signalen unter verwendung von leistungssystemen mit maximalem wirkungsgrad
EP19810902508 EP0086777A1 (fr) 1981-08-26 1981-08-26 Systeme de transfert de signaux modules avec un rendement maximum en utilisant des systemes de lignes
AU75855/81A AU7585581A (en) 1981-08-26 1981-08-26 System for maximum efficiency transfer of modulated signals utilizing line systems

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
PCT/US1981/001147 WO1983000787A1 (fr) 1981-08-26 1981-08-26 Systeme de transfert de signaux modules avec un rendement maximum en utilisant des systemes de lignes

Publications (1)

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WO1983000787A1 true WO1983000787A1 (fr) 1983-03-03

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EP (1) EP0086777A1 (fr)
JP (1) JPS59500297A (fr)
AU (1) AU7585581A (fr)
DE (1) DE3152946T1 (fr)
GB (1) GB2118408B (fr)
WO (1) WO1983000787A1 (fr)

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
AU577709B2 (en) * 1985-07-19 1988-09-29 Celcom Cellular Pty. Ltd. Interface for mobile telephone system

Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3729693A (en) * 1971-08-02 1973-04-24 R Dolby Compressor/expander switching methods and apparatus
US3795876A (en) * 1971-04-06 1974-03-05 Victor Company Of Japan Compression and/or expansion system and circuit
US4025723A (en) * 1975-07-07 1977-05-24 Hearing Health Group, Inc. Real time amplitude control of electrical waves
US4061874A (en) * 1976-06-03 1977-12-06 Fricke J P System for reproducing sound information
US4249042A (en) * 1979-08-06 1981-02-03 Orban Associates, Inc. Multiband cross-coupled compressor with overshoot protection circuit

Family Cites Families (3)

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Publication number Priority date Publication date Assignee Title
US3896379A (en) * 1974-06-10 1975-07-22 Gen Electric Intercom circuit for a radio transmitter and receiver
US4038494A (en) * 1975-06-17 1977-07-26 Fmc Corporation Digital serial transmitter/receiver module
DE2842945C3 (de) * 1978-10-02 1981-11-19 Licentia Patent-Verwaltungs-Gmbh, 6000 Frankfurt Schaltung zur Erzeugung eines Steuersignals zur Steuerung des Übertragungsmaßes von elektronisch steuerbaren Verstärkungs-oder Dämpfungsgliedern

Patent Citations (5)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3795876A (en) * 1971-04-06 1974-03-05 Victor Company Of Japan Compression and/or expansion system and circuit
US3729693A (en) * 1971-08-02 1973-04-24 R Dolby Compressor/expander switching methods and apparatus
US4025723A (en) * 1975-07-07 1977-05-24 Hearing Health Group, Inc. Real time amplitude control of electrical waves
US4061874A (en) * 1976-06-03 1977-12-06 Fricke J P System for reproducing sound information
US4249042A (en) * 1979-08-06 1981-02-03 Orban Associates, Inc. Multiband cross-coupled compressor with overshoot protection circuit

Also Published As

Publication number Publication date
GB8310309D0 (en) 1983-05-18
AU7585581A (en) 1983-03-08
EP0086777A1 (fr) 1983-08-31
DE3152946T1 (de) 1983-12-01
JPS59500297A (ja) 1984-02-23
GB2118408B (en) 1985-06-19
GB2118408A (en) 1983-10-26

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