US3622704A - Vocoder speech transmission system - Google Patents

Vocoder speech transmission system Download PDF

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US3622704A
US3622704A US884813A US3622704DA US3622704A US 3622704 A US3622704 A US 3622704A US 884813 A US884813 A US 884813A US 3622704D A US3622704D A US 3622704DA US 3622704 A US3622704 A US 3622704A
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pitch
period
shift registers
fundamental
pulses
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Gilbert M Ferrieu
Jean-Michel Person
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PERSON JEAN MICHEL
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PERSON JEAN MICHEL
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    • 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
    • H04B1/66—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 reducing bandwidth of signals; for improving efficiency of transmission
    • H04B1/667—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 reducing bandwidth of signals; for improving efficiency of transmission using a division in frequency subbands
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10L—SPEECH ANALYSIS TECHNIQUES OR SPEECH SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING TECHNIQUES; SPEECH OR AUDIO CODING OR DECODING
    • G10L19/00—Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis
    • G10L19/04—Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis using predictive techniques
    • G10L19/08—Determination or coding of the excitation function; Determination or coding of the long-term prediction parameters

Definitions

  • a channel vocoder speech transmission system including at the transmitter station a pitch detector circuit producing pitch marker pulses having a repetition period equal to the fundamental pitch period T of the speech to be transmitted, a pitch marker pulse sorter for eliminating spurious pitch marker pulses whose repetition period differs from said fundamental pitch period by a predetermined percentage of the fundamental pitch period and means for coding into PCM signals the pitch period and, at the receiver station, a
  • shift registers having unequal numbers M and N of stages with M N, two exclusive OR gates respectively associated with the shift registers, with inputs connected to the last and last but one stages of the shift registers and an output connected to the first stage thereof.
  • shift registers and OR gates form two generators of maximal length linear binary sequences.
  • the shift registers are controlled by shifting pulses having a repetition period equal to T/(2l PAIENTEDuuv 23 l97l SHEET u or 5 Q 5 GE INVENTORS:
  • This invention relates to speech transmission systems and is particularly concerned with narrow-band systems such as the spectrum channel vocodertransmittingthe infonnation content of wide-band speech waves in the form of a number of narrow-band control signals.
  • the spectrum channel vocoder is a method for speech analysis-synthesis employing a parametric description of the shorttime speech spectrum.
  • the spectral envelope of the signal is represented typically by 10 to 20 samples or channel control signals spaced along the frequency axis.
  • the spectral fine structure is represented by one additional parameter which measures the fundamental pitch frequency characteristic of voiced sounds and is equal to zero for unvoiced sounds or silence.
  • the excitation source is formed by a generator of maximal length linear binary sequencies, thatis by a shift register looped on-itself by an exclusive OR circuit. It is known that the maximal length linear binary sei uencies, although deterministic, have properties similar to those of white noise. The advantages of the use of generators of maximal length linear binary sequencies as an excitation source for a vocoder system are now explained.
  • the mean power density spectrum in the low frequencies is:
  • FIG. 1 is aschematic block diagram showing a complete channel vocoder system embodying the apparatus of this invention
  • FIG. 2 is a schematic block diagram showing apparatus for coding into PCM signals the channel control signals
  • FIG. 3 is a schematicblock diagram showing apparatus for decoding into analog signals the PCM channel control signals
  • FIG. 4 is a schematic block diagram showing the pitch detector and coder
  • FIG. 5 is a schematic block diagram showing the channel vocoder synthesizer.
  • FIGS. 6 and 7 are two spectrum diagrams useful for the explanation of the invention.
  • This frequency range typical of telephone sign'als, permits high intelligibilityand good quality.
  • the output of each filter is connected to afull-wave rectifier, respectively 4 to 4, and low-pass filter,'respectively 5 to 5,.
  • the outputs of the lowpass filters represent the time-varying average signal amplitudes-ofthe frequency-bands. Together these It channels control signals; represent the envelope of the short-time spectrum of the speech signal.
  • the channel control signals are coded into PCM signals of four bits by. coders 6,to 6,. controlled by clock pulse generator 7.
  • Thedi'gital'signals are applied to multiplexer 8 also controlled by clock' pulse generator 7 and transmitted over a reduced capacity transmission channel 9 to receiver station R.
  • the incomingspeech signal from microphone l is also applied to pitchdetector and coder 10.
  • pitchdetector and coder 10 A'detailed explanation of the operationand structure of pitch detector and coder 10 is given below in connection with FIG. 4.
  • conventional demultiplexer 11 passes the-coded channel control'signals' to decoders 12, to l2, which'may be of any well-known construction for convert- -ing four-bit signals into analog signals and passes the pitch and to passband-filters'lS, to 15,.
  • Modulators 14, to 14,. are
  • a clock pulse-generator 18 synchronous with 7 controls the demultiplexer 11 and the'decoders 12 to 12,.
  • the pitch detector and coder 10 comprises two pitch detectors 101 and 101' respectively connected directly and via inverter to the output of amplifier 2 and two pitch marker pulse sorters and coders 102 and 102'.
  • the circuits '101' and 101' on the one hand and the circuits 102 and 102 on the other hand are identical and only circuits 101 and 102 will be described later on.
  • the function of circuits 101 and 101' is to generate pitch marker pulses and the function of circuits l02 and 102' is to eliminate spurious marker pulses by'blocking the passage of those pitch marker pulses which follow a preceding pitch marker pulse within a predeterminedinhibition time interval.
  • IOIOIIJI Pitch detector 101 comprises two chains of circuits, a selector chain and a control chain.
  • the selector chain comprises an amplifier 103 having a low output impedance, a capacitor 104, a resistor 105, a transistor 106, an amplifier 107 and a monostable flip-fiop 108.
  • the capacitor 104 is serially connected at the output of amplifier 103 and the resistor 105 and the emitter-collector path of transistor 106 are connected in parallel on to the leads mutually connecting the two amplifiers 103 and 107.
  • the output of flip-flop 108 is connected to the base of transistor 106.
  • the control chain of pitch detector 101 comprises a threshold and differentiating amplifier 109 and a monostable flip-flop 110.
  • the output of monostable flip-flop 110 is connected to the automatic gain control (AGC) terminal of amplifier 107 of the selector chain.
  • AGC automatic gain control
  • the operation of the pitch detector is the following.
  • Amplifier 107 is blocked when no signal is applied thereto and its gain is very large when AGC terminal receives a pulse from flip-flop 110.
  • the amplifier 109 phase-shifts by 11/2 and clamps the speech signal, it produces a rectangular signal whose leading and trailing edges substantially coincide with the positive and negative peaks of the speech signal.
  • the edges which correspond to the positive peaks operate monostable flip-flop 110 which unblocks amplifier 107.
  • the pitch period would be determined by flip-flop 110 while disregarding the relative amplitude of the positive and negative peaks of the speech signal.
  • the function of the selector chain of the pitch detector is to control the operation of flip-flop 108 and to make it recopy or disregard the operation of flip-flop 110 according to whether the decay in the input signal amplitude since the last operation of the flip-flop 108 is larger or smaller than a given amount.
  • flip-flop 110 generates proposed marking pulses and flip-flop 108 confirms some of these pulses and omits the others.
  • Capacitor 104 can charge through transistor 106 in its conducting state and discharge through resistor 105. Conduction of transistor 106 is controlled by flip-flop 108. Let us assume that flip-flop 110 has just operated marking the beginning of a pitch period and that flip-flop 108 has simultaneously operated. Flip-flop 108 brings transistor 106 to its one state and capacitor 104 charges with respect to ground. Then flipflop 108 is restored to its zero state and capacitor 104 discharges through resistor 105. If at the beginning of next pitch period as determined by the control chain along the speech signal amplitude as reduced by the discharge of capacitor 104 across resistor 105 is higher than a given threshold at the input of amplifier 107, flip-flop 108 will be operated.
  • pitch detectors 101 and 101 produce pitch marker pulses corresponding to positive peaks as regards pitch detector 101 and negative peaks as regards pitch detector 101' regardless of whether these peaks are periodical or not.
  • the amplitude difference between the signal issuing from amplifier 103 and the signal applied to amplifier 107 depends on the time constant due to capacitor 104 and resistor 105 and on the duration of the discharge.
  • the minimum of this duration is the lower limit of the pitch period, say 2 ms. in order not to have more than one significant peak per minimal period, the above time constant is selected in such a way that the attenuation of a peak issuing from 103 generates in 2 ms. a signal lower than the threshold of amplifier 107.
  • the pitch marker pulse sorter and coder comprises a counter 121 which is supplied at its input terminal with clock pulses generated by clock pulse generator 7 and at its reset terminal by pitch marker pulses generated by monostable flipflop 108 and is connected to nonlinear time base generator 122.
  • Nonlinear time base generator 122 has four output terminals 122 to 122,. At terminal 122,, 122,, 122 there appear recurrent pulses corresponding to the three first clock pulses coming from clock pulse generator 7. At terminals 122 there appear successive nonperiodic pulses spaced apart from each other by increasing time-intervals T, such that:
  • the outputs of counter 123 are connected to the inputs of register 124 via AND-gate set 125 and to the inputs of comparator 126.
  • the outputs 'zero and one of comparator 126 are connected to the inputs zero and one of flip-flop 127 via AND-gate 128 and 129.
  • the zero output of flip-flop 127 is connected to AND- gate 140 together with a lead coming from 122
  • the output of AND-gate 140 controls a set of AND-gates 141 inserted between a register 144 and a buffer register not shown connected to multiplexer 8.
  • Register 144 is connected to the outputs of counter 121 via AND-gates 145.
  • the operation of the pitch marker pulse sorter and coder is the following.
  • Comparator 126 compares the bits of the coded pitch control signal of two successive pseudocycles except the lower weight bit. As the lower weight bit represents a time interval which increases when the coded pitch control signal increases due to the expansion in nonlinear decoder 122, it results that the predetermined inhibition time referred to in the introductory part increase with the pitch period.
  • Analog to PCM compression converters or coders are known in the art and such a coder is shown in FIG. 2.
  • the output signal of low-pass filter 5. 1 i S n) is applied to the input terminal 60,, of the coder 6. and is compared in comparator 61 to a series of predetermined voltages generated across resistor 601 by means of a matrix 610.
  • a comparison signal one is applied to flip-flop 602.
  • the one output of flip-flop 602 opens the AND gate 603 and counter 604 counts clock pulses produced by time-base 605.
  • Time-base 605 is synchronized by clock pulse generator 7.
  • the signals produced by counter 604 comprise four bits which are respectively applied to four output gates 611-614 and are divided into two groups of two bits which are respectively applied to decoders 606 and 607.
  • the four outputs of decoders 606 are connected to the four lines of matrix 610 and the four outputs of decoder 607 are connected to the four columns of the said matrix.
  • the crosspoints of the matrix are passing or blocked switches according to whether the line and column controlling a given cross-point are supplied with current or not.
  • the cross-points comprise also resistors in which a current can flow or not according to whether the switch is open or closed. All the columns of matrix 610 are connected in parallel to resistor 601.
  • the matrix resistors are given suitable values for complying with the compression law.
  • PCM to analog expansion converters or decoders are known in the art and such a decoder is shown in FIG. 3.
  • the coded channel control signals from demultiplexer 11 are applied respectively through terminals 120 to 120, to flipflops 1211 to 1214 of decoder 12, which control a digital attenuator 1200 supplied with direct current by current source 1201.
  • the flip-flops are reset by clock pulse generator 18 through terminal 120, and the analog signals are applied to modulator 14, through terminals 120
  • the purpose of circuit 13 is to produce a flat spectrum excitation signal over all the voice bandwidth which is formed by the fundamental component of the voice and its harmonics in the case of voiced signals, and is a white noise signal in the case of unvoiced sounds.
  • Generator 13 comprises two shift registers 130 and 131 the first formed of seven flip -flops 1301 to 1307 and the second of 11 flip-flops 1311 to 1321. These shift registers are looped afterthe fashion of a ring counter through two exclusive OR- gates 1300 and 1310 respectively, which receive at the same time the bits respectively in the last and last but one flip-flops of the associated shift register. The outputs of exclusive OR- gates 1300 and 1310 are connected respectively to one input of AND-gates 1381 and 1382. Registers 130 and 131 are known in the art as maximal length linear binary sequence generators.
  • the advance of both shift registers 130 and 131 is achieved by advance flip-flop 132.
  • the coded eight-bit pitch control signal is applied through input terminals 1321-1328 to register 133 and AND-gate 134. From register 133, this signal is applied to counting-down counter 135 through AND-gates 1361 to 1368.
  • Counting-down counter 135 comprises eight flip-flops 1351 to 1358 whose outputs are connected to AND-gate 137.
  • the output of AND-gate 137 is connected to the one input of flip-flop 132 through inverter 1383.
  • Counting-down counter 135 is driven by time base 138 which produces high-rate clock pulses, of 2 MHz. frequency for example.
  • AND-gate 134 is connected through inverter 1384, to the one input of flip-flop 139 and to one of the inputs of AND-gate 1385.
  • the one and zero outputs of flip-flops 139 are connected respectively to the second inputs of AND-gates 1381 and 1382.
  • the clock pulses from generator 18 are apto AND-gate 1385 and to flip-flop 139 for resetting it.
  • excitation circuit 13 The operation of excitation circuit 13 is the following.
  • T l6 ms. and is expressed in an eight-bit pitch control number; it results that the lower weight bit of this number represents 1/256 of 16 ms., that is approximately 64 sec.
  • the decimal translation of the pitch control number represents T divided by 64 ,u. sec. for a pitch period of Tseconds, that is the number l T/64 wherein Tis expressed in seconds.
  • the multiplex period is assumed to:be 25 ms. which corresponds to a frequency of 40 Hz.
  • the pitch control coded'signal or number is applied at an instant which will be defined later on to counter 135 which counts down to zero, the count zero being detected by gate 137.
  • the output signal of gate 137 triggers flip-flop 132 which opens gates 1361 to 1368 and advances by one step shift registers 130 and 131.
  • a new pitch control coded signal is entered into counter 135.
  • the spectrum of the maximal length linear binary sequence issuing from shift register 130 is represented in FIG. 6 and the spectrum of the maximal length linear binary sequence issuing from shift register 131 is represented in FIG. 7
  • the spectrum is quite flat up to 3,500 Hz. and comprises a harmonic every 62.5 112., that is 53 harmonics between 200 and 3,500 Hz.
  • the spectrum of FIG. 7 comprises 16 times more harmonics than the spectrum of FIG. 6 and, due to low spacing between harmonics, it resembles a white noise.
  • a channel vocoder speech transmission system including at the transmitter station a pitch detector circuit producing pitch marker pulses, the majority of which have a repetition period equal'to the fundamental pitchperiod T of the speech to be transmitted, a pitch marker pulse sorter fed by said pitch marker pulses and adapted to eliminate therefrom spurious pitch marker pulses whose repetition period differs from said fundamental pitch period by a predeten'nined percentage of the fundamental pitch period and to retain normal pitch marker pulses whose repetition period is equal to said fundamental pitch period and means for coding into PCM signals the intervals between the normal pitch marker pulses and, at the receiver station means for receiving said PCM signals and deriving therefrom the pitch period T, two shift registers having unequal numbers M and N 'of stages with M N, two exclusive OR gates respectively associated with the shift registers, with inputs connected to the last and penultimate stages of the shift registers and an output connected to the first stage thereof, means for generating pulses of a given repetition period for synchronously advancing said shift registers and means for controlling said given repetition
  • A'channel vocoder speech transmission system including at the transmitter station a pitch detector circuit producing pitch marker pulses the majority of which have a repetition period equal to the fundamental pitch period T of the speech to be transmitted, a pitch marker pulse sorter fed by said pitch marker pulses and adapted to eliminate therefrom spurious pitch marker pulses whose repetition period differs from said fundamental pitch period and to retain normal pitch marker pulses whose repetition period is equal to said'fundamental pitch period and means for coding into PCM signals the intervals between 'the normal pitch marker pulses and, at the receiver station means for receiving said PCM signals and deriving therefrom the pitch period T, two shift registers having unequal number M and N of stages with M N, two exclusive OR gates respectively associated with the shift registers with input connected to the last and penultimate stages of the shift registers and an output connected to the first stage thereof, means for generating pulses of a given repetition period for synchronously advancing said shift registers, means for controlling said given repetition period and equalizing it to T/(2" -A), means for
  • a channel vocoder speech transmission system as set forth in claim 3 in which r 2(10) Hertz

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  • Engineering & Computer Science (AREA)
  • Signal Processing (AREA)
  • Computer Networks & Wireless Communication (AREA)
  • Computational Linguistics (AREA)
  • Health & Medical Sciences (AREA)
  • Audiology, Speech & Language Pathology (AREA)
  • Human Computer Interaction (AREA)
  • Physics & Mathematics (AREA)
  • Acoustics & Sound (AREA)
  • Multimedia (AREA)
  • Compression, Expansion, Code Conversion, And Decoders (AREA)
US884813A 1968-12-16 1969-12-15 Vocoder speech transmission system Expired - Lifetime US3622704A (en)

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Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3852535A (en) * 1972-11-16 1974-12-03 Zurcher Jean Frederic Pitch detection processor
EP0070949A1 (de) * 1981-07-28 1983-02-09 International Business Machines Corporation Übertragungsverfahren für Sprache und digitale Daten und Ausführungsanordnung für das genannte Verfahren
FR2545966A1 (fr) * 1983-05-09 1984-11-16 Zurcher Jean Frederic Procede d'elaboration d'un signal d'excitation pour synthetiseur de parole a canaux ou a prediction lineaire et generateur de signal d'excitation pour un tel synthetiseur
US20040093206A1 (en) * 2002-11-13 2004-05-13 Hardwick John C Interoperable vocoder
US20050278169A1 (en) * 2003-04-01 2005-12-15 Hardwick John C Half-rate vocoder
US20080154614A1 (en) * 2006-12-22 2008-06-26 Digital Voice Systems, Inc. Estimation of Speech Model Parameters
US20100094620A1 (en) * 2003-01-30 2010-04-15 Digital Voice Systems, Inc. Voice Transcoder
US11270714B2 (en) 2020-01-08 2022-03-08 Digital Voice Systems, Inc. Speech coding using time-varying interpolation
US11990144B2 (en) 2021-07-28 2024-05-21 Digital Voice Systems, Inc. Reducing perceived effects of non-voice data in digital speech

Families Citing this family (1)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE19806927A1 (de) * 1998-02-19 1999-08-26 Abb Research Ltd Verfahren und Einrichtung zur Übertragung natürlicher Sprache

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2892892A (en) * 1955-10-07 1959-06-30 Bell Telephone Labor Inc Vocoder absorption modulation system
US3109142A (en) * 1960-10-06 1963-10-29 Bell Telephone Labor Inc Apparatus for encoding pitch information in a vocoder system
US3124654A (en) * 1964-03-10 Transmitter

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3124654A (en) * 1964-03-10 Transmitter
US2892892A (en) * 1955-10-07 1959-06-30 Bell Telephone Labor Inc Vocoder absorption modulation system
US3109142A (en) * 1960-10-06 1963-10-29 Bell Telephone Labor Inc Apparatus for encoding pitch information in a vocoder system

Cited By (17)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3852535A (en) * 1972-11-16 1974-12-03 Zurcher Jean Frederic Pitch detection processor
EP0070949A1 (de) * 1981-07-28 1983-02-09 International Business Machines Corporation Übertragungsverfahren für Sprache und digitale Daten und Ausführungsanordnung für das genannte Verfahren
FR2545966A1 (fr) * 1983-05-09 1984-11-16 Zurcher Jean Frederic Procede d'elaboration d'un signal d'excitation pour synthetiseur de parole a canaux ou a prediction lineaire et generateur de signal d'excitation pour un tel synthetiseur
EP0128065A1 (de) * 1983-05-09 1984-12-12 Jean-Frédéric Zurcher Verfahren, um ein Anregungssignal für einen Kanal- oder linearen Prädiktionsynthesizer zu erzeugen und Anregungssignalgenerator für diesen Synthesizer
US20040093206A1 (en) * 2002-11-13 2004-05-13 Hardwick John C Interoperable vocoder
US8315860B2 (en) 2002-11-13 2012-11-20 Digital Voice Systems, Inc. Interoperable vocoder
US7970606B2 (en) * 2002-11-13 2011-06-28 Digital Voice Systems, Inc. Interoperable vocoder
US7957963B2 (en) 2003-01-30 2011-06-07 Digital Voice Systems, Inc. Voice transcoder
US20100094620A1 (en) * 2003-01-30 2010-04-15 Digital Voice Systems, Inc. Voice Transcoder
US20050278169A1 (en) * 2003-04-01 2005-12-15 Hardwick John C Half-rate vocoder
US8359197B2 (en) 2003-04-01 2013-01-22 Digital Voice Systems, Inc. Half-rate vocoder
US8595002B2 (en) 2003-04-01 2013-11-26 Digital Voice Systems, Inc. Half-rate vocoder
US20080154614A1 (en) * 2006-12-22 2008-06-26 Digital Voice Systems, Inc. Estimation of Speech Model Parameters
US8036886B2 (en) 2006-12-22 2011-10-11 Digital Voice Systems, Inc. Estimation of pulsed speech model parameters
US8433562B2 (en) 2006-12-22 2013-04-30 Digital Voice Systems, Inc. Speech coder that determines pulsed parameters
US11270714B2 (en) 2020-01-08 2022-03-08 Digital Voice Systems, Inc. Speech coding using time-varying interpolation
US11990144B2 (en) 2021-07-28 2024-05-21 Digital Voice Systems, Inc. Reducing perceived effects of non-voice data in digital speech

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DE1962759B2 (de) 1971-05-13
FR1602217A (de) 1970-10-26
NL6918854A (de) 1970-06-18
DE1962759A1 (de) 1970-06-18
GB1260735A (en) 1972-01-19
BE743226A (de) 1970-05-28

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