US3569603A - Moving formant band-pass amplifier for an electronic musical instrument - Google Patents

Moving formant band-pass amplifier for an electronic musical instrument Download PDF

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Publication number
US3569603A
US3569603A US749334A US3569603DA US3569603A US 3569603 A US3569603 A US 3569603A US 749334 A US749334 A US 749334A US 3569603D A US3569603D A US 3569603DA US 3569603 A US3569603 A US 3569603A
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voltage
circuit
called
formant
moving formant
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US749334A
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English (en)
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Donald R Kern
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Marmon Co
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Hammond Corp
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    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10H—ELECTROPHONIC MUSICAL INSTRUMENTS; INSTRUMENTS IN WHICH THE TONES ARE GENERATED BY ELECTROMECHANICAL MEANS OR ELECTRONIC GENERATORS, OR IN WHICH THE TONES ARE SYNTHESISED FROM A DATA STORE
    • G10H1/00—Details of electrophonic musical instruments
    • G10H1/02—Means for controlling the tone frequencies, e.g. attack or decay; Means for producing special musical effects, e.g. vibratos or glissandos
    • G10H1/06—Circuits for establishing the harmonic content of tones, or other arrangements for changing the tone colour
    • G10H1/14—Circuits for establishing the harmonic content of tones, or other arrangements for changing the tone colour during execution
    • 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
    • G10L25/00—Speech or voice analysis techniques not restricted to a single one of groups G10L15/00 - G10L21/00
    • G—PHYSICS
    • G10—MUSICAL INSTRUMENTS; ACOUSTICS
    • G10H—ELECTROPHONIC MUSICAL INSTRUMENTS; INSTRUMENTS IN WHICH THE TONES ARE GENERATED BY ELECTROMECHANICAL MEANS OR ELECTRONIC GENERATORS, OR IN WHICH THE TONES ARE SYNTHESISED FROM A DATA STORE
    • G10H2250/00—Aspects of algorithms or signal processing methods without intrinsic musical character, yet specifically adapted for or used in electrophonic musical processing
    • G10H2250/471—General musical sound synthesis principles, i.e. sound category-independent synthesis methods
    • G10H2250/481—Formant synthesis, i.e. simulating the human speech production mechanism by exciting formant resonators, e.g. mimicking vocal tract filtering as in LPC synthesis vocoders, wherein musical instruments may be used as excitation signal to the time-varying filter estimated from a singer's speech
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10S84/00—Music
    • Y10S84/10—Feedback

Definitions

  • a circuit for achieving the moving or changing formant effect in an electronic musical instrument such as an electric organ employs a band-pass amplifier with parallel T resistive-capacitive feedback circuits in which an FET (Field Effect Transistor) is employed as a variable resistance to cut in, by degrees, one of the T feedback circuits.
  • the effective resistance of the FET and thus the band-pass of the amplifier are varied by a capacitive and resistive timing circuit that is controlled via a keying circuit from one or more keys or other player-operated controls, such as the manual keys of an electric organ.
  • the present invention has as its general object the provision of a moving formant device of a new and improved construction.
  • a more specific object of the invention is the provision of such a device that is both effective in use and economical to make and maintain.
  • One object of the present invention is the provision of a moving formant device which may affect only a portion of the note voiced while leaving the other portion unaffected.
  • FIG. 1. is an electric circuit diagram of a moving formant device constructed in accordance with the principles of the present invention.
  • FIG. 2 is an electric circuit diagram of another moving formant device constructed in accordance with the invention.
  • FIG. 1 the device there depicted is generally designated by the numeral and forms part of an electrical musical instrument of the electric organ type.
  • the organ includes a bright bus 11 from which an electrical musical tone may be taken. Playing key contacts or keyers, not shown since they may be conventional, will key the proper signals to the bus 11 as particular playing keys areactuated.
  • a selector switch 12 couples the output of bus bar 11 to a band-pass amplifier generally designated 9.
  • the amplifier 9 may be consideredto be a two transistor parallel T feedback oscillator in which one of the feedbacks T has been slightly detuned, thus preventing oscillation but instead resulting in a resonant peak in the audio spectrum at approximately the oscillator frequency.
  • the switch 12 is directly connected to one side of a capacitor 13.
  • a resistance 14 is connected from that side of capacitor 13 to a plane of reference potentialor ground.
  • the other side of capacitor 13 is connected through a resistor 15 to the base of a first transistor 16 of the NPN type.
  • Also connected to the base of transistor 16 is one end of a resistor 17, whose other end is grounded, and one end of a resistor 18 whose other end is connected to a source of direct current biasing potential B+.
  • the emitter of the first transistor 16 is connected to the base of a second NPN transistor 19.
  • a resistor 20 is connected from the interconnected emitter of transistor 16 and base of transistor 19 to ground.
  • the collectors of both transistors 16 and 19 are connected together and through a resistor 21 to the voltage source 13+.
  • the emitter of transistor 19 is connected through a resistor 22 and a parallel connected capacitor 23 and resistor 24 to ground.
  • the collectors of the transistors 16 and 19 are connected together and through a direct current blocking capacitor 25 to an output terminal 26, connected in turn to conventional musical instrument amplifiers and mixing circuits which supply signals at an appropriate level to one or more speakers 71.
  • the terminal 26 also is connected via a line 27 to a feedback network generally designated 28.
  • the network 28 feeds back the output at terminal 26, via a line 29 and through a capacitor 30, to the base of the transistor 16.
  • the circuit 28 includes a first T network of a pair of series connected resistors 31 and 32 whose joined ends are connected through a capacitor 33 to ground and whose free ends are connected respectively to the lines 27 and 29.
  • the circuit 28 also includes a second T network comprising a pair of series connected capacitors 34 and 35 whose common ends are connected through a variable resistance 36 to ground.
  • the free end of capacitor 35 is connected to line 29 and also through another capacitor 37 to ground.
  • the free end of capacitor 34 is connected through a resistor 38 to ground.
  • FET 40 Field-Effect Transistor 40 of the p-channel type.
  • the FET is a well known device now in commercial use. Those unfamiliar with its characteristics are referred to "Field Effect Transistors," by L. .I. Sevin, Jr., McGraw, Hill, 1965. Reference also may be made to Application Note AN-2l l of Motorola Semiconductor Products, Inc. entitled Field Effect Transistors in Theory and Practice" by J F. Kane et al., dated Sept. 1966.
  • the drain of the FET 40 is connected to line 27 and the source of FET 40 is connected to the series junction of capacitor 34 and resistor 38.
  • the gate of the FET 40 is connected to the movable tap of a variableresistor 41 which has one end grounded and the other end connected to one end of a fixed resistor 42.
  • the junction between these resistors is connected to ground through a timing capacitor 43.
  • the other end of the fixed resistor 42 is connected through the collector emitter circuit of a transistor 45 to ground and through a resistor 46 to 8+.
  • the transistor 45 is of NPN type, has its emitter grounded and has its base connected to one contact 44 of a single pole, single throw selector switch 47, the other side of which is grounded. When the switch 47 is open, the bias of base of transistor 45 is determined by a keying circuit generally designated by the numeral 50.
  • the keying circuit 50 may be anything suitable. but as shown consists of a circuit from the base of transistor 45 through a current limiting resistor 48 to a pair of NPN transistors 51 and 52.
  • the transistor 51 has its collector connected to the resistor 48 and also to the bias source 13+ through a resistor 53. Its emitter is grounded and the base is connected to the collector of the transistor 52 and through a resistor 54 to the bias source B+.
  • the base of the transistor 52 is connected to the series junction of a pair of resistors 55 and 56 which are connected in order between the bias source 8+ and ground.
  • a diode 57 oriented to pass current from the base of transistor 52 to ground.
  • the emitter of transistor 52 is connected to ground through a diode 58 and resistor 59in parallel.
  • the diode 58 is oriented to allow current flow only from the emitter of transistor 52 to ground.
  • the emitter of transistor 52 is also connected to one side of a normally open control'switch 60 which typically will be closed by actuation of the organ playing keys.
  • the other side of the switch 60 is connected, through a current limiting resistor 61 to a source of positive potential, designated B'+ at above 4v.
  • the biasing for the transistors 16 and 19 as established by the voltage source 8+ and the resistors associated with the transistors, is such as to cause them to operate in class A amplification.
  • the FET is similarly biased as to operate as a variable resistance between its drain and source. I
  • the device 10 may deliver to the amplifying and m'iiting circuit 70 a musical tone signal which exhibits the moving formant effect in response to the closing of the key switch 60.
  • the circuit With the selector switch 47 closed, so that the contact 44 is grounded, the circuit does not respond to the key contacts 60, but delivers a musical tone signal at its output terminal 26 which approximates a trumpet note in its character and does not exhibit a moving formant effect.
  • the signal from the bright bus 11 is transferred through the capacitor 13 and resistor 15 to the base of the transistor 16.
  • the transistors 16 and 19 amplify this signal and supply it to the output terminal 26 through the capacitor 25.
  • the feedback circuit 28 has two feedback paths, one via line 27, the T circuit of resistors 31 and 32 and line 29; and another through the drain-source circuit of the FET 40, the capacitors 34 and 35 and line 29.
  • the effective resistance of the drain source circuit of the FET 40 controls or modulates the signal that passes through this second path.
  • the feedback circuit is an RC twin T-frequency rejection network which has been split such that the output signal of transistor 19 is applied to half of the network (31-32-33) while a variable voltage, but otherwise similar signal, is applied to the other network half (34-35-36).
  • the rejection frequency therefore, varies depending upon conduction through the FET.
  • the amplifier 9 is, therefore, of the band-pass type and has its band-pass determined by the capacitive resistive feedback circuit 28.
  • the second feedback path is effectively cut out of the circuit and the band-pass of the amplifier 9 is centered about one high resonance peak.
  • the alternate path is fully open and the band-pass of the amplifier 9 is centered about a low resonance peak.
  • the movement of the band-pass of the amplifier 9 from its low to high resonant peak is thus governed by the effective drain source resistance of the FET 40 which resistance is in turn governed by the direct current bias on its gate.
  • the voltage on the gate is determined by the timing circuit of the resistances 41 and 42 and the capacitor 43.
  • the capacitor 43 discharges through resistor 42 as well as through permanently connected resistor 41. If the value of the resistor 42 is chosen to be small in comparison to that of resistor 41 a fast decline of the voltage at the gate of the FET 40 will be achieved, approximating the curve 73 of the small graph of FIG. 1.
  • the transistor 45 is rendered nonconductive by grounding its base. This may be done by the trumpet selector switch 47 or by the keying circuit 50 in response to closure of the key contacts 60.
  • the band-pass of the amplifier is fixed at its high peak and the tone signal produced at output terminal 26 is like a trumpet and does not have the moving formant effect.
  • the band-pass amplifier 9 will normally be at its low band-pass peak and a muted trumpet sound electrical signal will be translated through the amplifier 9 to the output terminal 26.
  • the key contacts 60 are closed, the potential at the emitter of the transistor 52 is caused to rise to the threshold value of diode 58, cutting off that transistor and turning on the transistor 51.
  • Transistor 16 is of the 2N339lA type, transistors 19, 45, 51 and 52 are of the 2N3393 type.
  • the FET 40 is of 2N3819 type.
  • the diodes 57 and 58 are of typical silicon junction type and are used to establish a potential at their threshold value of about 0.6V. They aid in temperature compensating the circuit.
  • the impressed signal from the bright bus bar 11 is normally at about 10.7v. peak-to-peak.
  • the components were chosen to provide a formant movement of about l /aoctaves, with the high resonant peak providing a formant similar to the normal 8' trumpet stop on a typical electrical organ.
  • FIG. 2 an alternative circuit for the moving formant device is there depicted and is similarly generally indicated by the numeral 10'.
  • Elements of this embodiment which are similar to those of the previous embodiment will be identified with primes of the same numbers, it being understood that they are connected as in the previously described embodiment unless noted to the contrary.
  • the values of the otherwise similar components may be different, however.
  • the device 10 includes an amplifier 9 generally similar to the amplifier 9 of the previous embodiment, except that it includes an NPN transistor 80 in place of the FET 40 and a parallel inductor 81 and capacitor 82 in place of the load resistor 2].
  • the resistance of the emitter-collector circuit of transistor 80 is controlled by either a simplified keying circuit 83 or by a low-frequency oscillator circuit 84, either of which may be connected to the base of transistor 80, depending upon the position of a selector switch 85.
  • the amplifier 9 includes an input terminal 86 which is connected to one end of a resistor 15' whose other end is connected to the base of an NPN transistor 16'. This base also is connected through a resistor 18 to B+ and through a resistor 17' to ground.
  • the emitter of the transistor 16' is connected to the base of an NPN transistor 19 and the collectors of both transistors 16' and 19' are connected together and through a parallel capacitor 82-inductor 81 circuit to B+, and also to a signal output terminal 26 and to a feedback circuit 28 via a line 27.
  • the emitter of transistor 19 is connected to ground through a parallel connected resistor 24' and capacitor 23'.
  • the circuit 28 comprises a pair of T circuits, one of resistors 31', 32 and capacitor 33 and the other of capacitors 34, 35' and variable resistor 36, the latter being connected to lead 37 by way of the collectoremitter circuit of a transistor 80.
  • the other side of circuit 28' is connected to the base of transistor 16 through a line 29' and a capacitor 30.
  • the collector of transistor 80 is connected to lead 27 and a capacitor 87 is connected between the collector and its base.
  • the base is also connected through a resistor 46 to B+ and through a resistor 41' to ground and through a resistor 88 to the blade ofthe previously mentioned switch 85.
  • the switch blade is also connected to ground through a timin gcapacitor 43'.
  • the keying circuit 83 by way of a line 89, is connected to one of two contacts that the blade of switch 85 may engage.
  • Line 89 is connected to the collector of a transistor 90 and also through a resistor 91 to B+.
  • the emitter of the transistor 90 is coupled through a resistor 92 to ground, and the base of that transistor is connected through a resistor 93 to B'+ and through a resistor 94 to ground.
  • the base of transistor 90 is also connected through a current limiting resistor 95 to B'+ by way of key actuated contacts 60.
  • the low-frequency frequency oscillator 84 which runs at vibrato rate, about 6.5 H includes a pair of NPN transistors 96 and 97 whose collectors are connected in common and,
  • the emitter of transistor 96 is connected through a resistor 101 to ground while the emitter of transistor 97 is connected to the base of transistor 96.
  • the base of transistor 97 is connected through a resistor 102 to its collector and through a resistor 103 to ground.
  • the base is also connected to one side of a capacitor 104, the other side of which is connected, through a variable resistor .105, to ground and to one side of another capacitor 106.
  • the other side of this capacitor 106 is connected through another variable resistor 107 to ground and to one side of yet another capacitor 108.
  • the other side of this capacitor is connected to the collectors of the transistors 96 and 97.
  • variable resistors are mechanically ganged and manually controlled to vary the oscillation rate.
  • the variable resistance 100 varies the swing limits or the degree of movement per oscillation when the oscillator 84 drives the moving formant of the amplifier 9.
  • the device when the blade of the selector switch 85 is connected to the oscillator circuit 84 functions to move the formant signal transferred through the amplifier 9 cyclically at a rate determined by the oscillator 84, for example at 6.5 to 7 cycles per second. This yields a pleasing musical effect which is somewhat like a vibrato.
  • the switch 85 When the switch 85 has its blade connected to line 89, it functions much as the embodiment of FIG. 1 when the switch 47 of thatembodiment is open. That is, a formant movement is produced in response to the closure of the key actuated switch *60.
  • the bias source B+ is 15 volts, while that of B'+ is 4 volts as previously stated.
  • This device 10 as shown and described effectively moves a formant slightly more than two octaves either under control of the playing keys or optionally under the influence of a repetitive voltage sources such as the vibrato oscillator.
  • the trumpet stop of an organ played through this device under key control sounds like a mute trumpet being opened up as the playing key is held.
  • the device 10 or 10' is in keying it with a touch responsive system on the upper manual and with the bright wave voices fed through it.
  • this device When this device is driven at the vibrato rate, it sounds very much like vibrato on the frequencies in the formant range. Since the formant range with the components as shown in FIG. 2 and values as detailed above, is from 400 cycles to l900 cycles, it is possible to play low-frequency bright wave tones in which the higher frequencies appear to have vibrato without the lower frequencies being affected. With proper selection of formant range, this device is effective to provide rnanual selection of vibrato within a limited frequency range on organs that normally have only unitary vibrato.
  • this invention provides a new and improved moving formant device that is versatile and capable of several applications in electrical musical instruments. Furthermore, it is relatively inexpensive as it employs low cost components, while effectively accomplishing its intended ends in an efficient manner.
  • a musical instrument moving formant device comprising an audio frequency amplifier having a music signal input and an amplified output, means providing a feedback :path connected forzfeeding back signal from said output to saidtinput,
  • said feedback path consisting of an RC, parallel T, frequency rejection circuit, one of the parallel branches of said circuit comprising a pair of resistors in series with a center connected capacitor and the other of the parallel branches comprising a pair of series connected capacitors with a center connected resistor.
  • a voltage dependent variable impedance incorporated in one only of said branches and connected so that conduction through the last said branch from said output to said input depends upon the voltage applied to said voltage de- V pendent variable impedance, and means connected for applying a variable control voltage to said variable impedance to vary the conduction through one only of the parallel branches as a function of said control voltage.
  • the means for applying the variable control voltage comprises a timing circuit of the type for providing a-gradual change of voltage for a few seconds followed by a steady voltage when activated and a rapid restoration of voltage to the original level when subsequently deactivated, and a manual control connected for activating and deactivating said timing circuit.
  • variable impedance device is incorporated in the branch which has the two capacitors in series and a center connected resistor.
  • the means for applying the variable control voltage comprises a timing circuit of the type which provides a gradual voltage change as a function of time for a few seconds followed by a steady state voltage when actuated and a rapid restoration to the original state when subsequently deactivated, and manual means connected for activating and deactivating said timing circuit.
  • -A second embodiment of the moving formant circuit employs a transistor in place of the FET, an: inductive-capacitive load for the amplifier that com sates for the frequency shift of the amplifier s out to produce a generally constant subjective tone ampl: tude therefrom, and an alternate circuit for activat: the formant change comprising a variable low frequem oscillator.
  • Driving the formant changing transistor the oscillator operating at vibrato speeds results i1 a musical effect similar to vibrato.

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  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Acoustics & Sound (AREA)
  • Multimedia (AREA)
  • Computational Linguistics (AREA)
  • Signal Processing (AREA)
  • Health & Medical Sciences (AREA)
  • Audiology, Speech & Language Pathology (AREA)
  • Human Computer Interaction (AREA)
  • Electrophonic Musical Instruments (AREA)
US749334A 1968-08-01 1968-08-01 Moving formant band-pass amplifier for an electronic musical instrument Expired - Lifetime US3569603A (en)

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US (1) US3569603A (enrdf_load_stackoverflow)
BE (1) BE736933A (enrdf_load_stackoverflow)
DE (1) DE1939029A1 (enrdf_load_stackoverflow)
GB (1) GB1210186A (enrdf_load_stackoverflow)

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3659031A (en) * 1969-10-10 1972-04-25 Nippon Musical Instruments Mfg Monophonic electronic musical instrument with a variable frequency oscillator employing positive feed back
US3749809A (en) * 1970-10-05 1973-07-31 Nippon Musical Instruments Mfg Circuit arrangement capable of continuously varying tone colors for electrical musical instruments
US3758872A (en) * 1971-09-23 1973-09-11 Honeywell Inc Fast recovery circuit for ac amplifier
US3763438A (en) * 1971-09-23 1973-10-02 Honeywell Inc Fast recovery circuit for ac amplifier
US3872764A (en) * 1973-06-15 1975-03-25 Baldwin Co D H Sample and hold circuit for an electric organ
US3880039A (en) * 1974-02-26 1975-04-29 Baldwin Co D H Sample and hold circuit for an electronic organ
US3919648A (en) * 1973-06-15 1975-11-11 Baldwin Co D H Voltage-controlled filter
US3924456A (en) * 1973-08-17 1975-12-09 Western Electric Co Methods and apparatus for detecting the presence of cracks in a workpiece by the use of stress waves emitted therefrom
US4160402A (en) * 1977-12-19 1979-07-10 Schwartz Louis A Music signal conversion apparatus
US4216434A (en) * 1977-02-22 1980-08-05 Licentia Patent-Verwaltungs-G.M.B.H. Variable gain alternating voltage amplifier
US4322995A (en) * 1979-06-07 1982-04-06 Tavel Donald L Music synthesizer
CN110491413A (zh) * 2019-08-21 2019-11-22 中国传媒大学 一种基于孪生网络的音频内容一致性监测方法及系统

Families Citing this family (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3897709A (en) * 1973-04-11 1975-08-05 Nippon Musical Instruments Mfg Electronic musical instrument
US3948139A (en) * 1974-08-28 1976-04-06 Warwick Electronics Inc. Electronic synthesizer with variable/preset voice control
DE2535344C2 (de) * 1975-08-07 1985-10-03 CMB Colonia Management- und Beratungsgesellschaft mbH & Co KG, 5000 Köln Einrichtung zum elektronischen Erzeugen von Klangsignalen

Citations (6)

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US2245365A (en) * 1940-01-31 1941-06-10 Rca Corp Audio-frequency amplifier
US2927282A (en) * 1958-04-24 1960-03-01 Gardberg Joseph Oscillator and filter circuits
US2971161A (en) * 1958-09-24 1961-02-07 Bendix Corp I.f amplifier with electronically controllable band-pass
US3205294A (en) * 1963-01-07 1965-09-07 Motorola Inc Electronic musical instrument
US3379820A (en) * 1964-12-02 1968-04-23 David G. Olson Electronic musical instrument
US3433937A (en) * 1964-10-28 1969-03-18 Beckman Instruments Inc Time shared integration circuit

Patent Citations (6)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2245365A (en) * 1940-01-31 1941-06-10 Rca Corp Audio-frequency amplifier
US2927282A (en) * 1958-04-24 1960-03-01 Gardberg Joseph Oscillator and filter circuits
US2971161A (en) * 1958-09-24 1961-02-07 Bendix Corp I.f amplifier with electronically controllable band-pass
US3205294A (en) * 1963-01-07 1965-09-07 Motorola Inc Electronic musical instrument
US3433937A (en) * 1964-10-28 1969-03-18 Beckman Instruments Inc Time shared integration circuit
US3379820A (en) * 1964-12-02 1968-04-23 David G. Olson Electronic musical instrument

Cited By (12)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3659031A (en) * 1969-10-10 1972-04-25 Nippon Musical Instruments Mfg Monophonic electronic musical instrument with a variable frequency oscillator employing positive feed back
US3749809A (en) * 1970-10-05 1973-07-31 Nippon Musical Instruments Mfg Circuit arrangement capable of continuously varying tone colors for electrical musical instruments
US3758872A (en) * 1971-09-23 1973-09-11 Honeywell Inc Fast recovery circuit for ac amplifier
US3763438A (en) * 1971-09-23 1973-10-02 Honeywell Inc Fast recovery circuit for ac amplifier
US3872764A (en) * 1973-06-15 1975-03-25 Baldwin Co D H Sample and hold circuit for an electric organ
US3919648A (en) * 1973-06-15 1975-11-11 Baldwin Co D H Voltage-controlled filter
US3924456A (en) * 1973-08-17 1975-12-09 Western Electric Co Methods and apparatus for detecting the presence of cracks in a workpiece by the use of stress waves emitted therefrom
US3880039A (en) * 1974-02-26 1975-04-29 Baldwin Co D H Sample and hold circuit for an electronic organ
US4216434A (en) * 1977-02-22 1980-08-05 Licentia Patent-Verwaltungs-G.M.B.H. Variable gain alternating voltage amplifier
US4160402A (en) * 1977-12-19 1979-07-10 Schwartz Louis A Music signal conversion apparatus
US4322995A (en) * 1979-06-07 1982-04-06 Tavel Donald L Music synthesizer
CN110491413A (zh) * 2019-08-21 2019-11-22 中国传媒大学 一种基于孪生网络的音频内容一致性监测方法及系统

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GB1210186A (en) 1970-10-28
BE736933A (enrdf_load_stackoverflow) 1970-02-02
DE1939029B2 (enrdf_load_stackoverflow) 1970-12-17
DE1939029A1 (de) 1970-03-19

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