US3660603A - Speech-controlled bilateral amplifier - Google Patents

Speech-controlled bilateral amplifier Download PDF

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Publication number
US3660603A
US3660603A US853881A US3660603DA US3660603A US 3660603 A US3660603 A US 3660603A US 853881 A US853881 A US 853881A US 3660603D A US3660603D A US 3660603DA US 3660603 A US3660603 A US 3660603A
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Prior art keywords
signal
input
control
circuits
channel
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Expired - Lifetime
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US853881A
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English (en)
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Bjorn Andersen
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US Philips Corp
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US Philips Corp
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Priority claimed from NO336968A external-priority patent/NO123134B/no
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    • H—ELECTRICITY
    • H04—ELECTRIC COMMUNICATION TECHNIQUE
    • H04M—TELEPHONIC COMMUNICATION
    • H04M9/00—Arrangements for interconnection not involving centralised switching
    • H04M9/08—Two-way loud-speaking telephone systems with means for conditioning the signal, e.g. for suppressing echoes for one or both directions of traffic
    • H04M9/10—Two-way loud-speaking telephone systems with means for conditioning the signal, e.g. for suppressing echoes for one or both directions of traffic with switching of direction of transmission by voice frequency

Definitions

  • ABSTRACT [30] Foreign Application Priority Data
  • a speech-controlled bidirectional amplifier that includes first Aug. 29, 1968 Norway ..3369/68 an econd transmission channels each with a control member 7 controlled by speech signals derived at control points preced- [52] US. Cl. ..179/1 VC, 179/1 H ing the control member.
  • First and second comparison devices [51] Int. Cl. ..H03g 3/24 responsive to the levels of the speech signals control a third Field of Search 1 VC, 1 F5, 170 R, comparison device that in turn controls the attenuation level 179/170 B, 1 31 170-6 of the control members.
  • the amplifier is arranged so that in the rest condition both control members provide a high signal [5 6] References and attenuation.
  • each amplifying channel includes a control member governed by a control circuit to which speech signals are applied that are taken from the two amplifying channels at points preceding the control member of each channel.
  • Such amplifiers may be employed with loud-speaking telephones or so-called intercom systems which allow a conversation in two directions.
  • the inputs of the amplifiers are connected to microphones and the output to loud speakers, the microphone of one channel being located in the same room as the loudspeaker of the other channel and conversely.
  • the associated amplifying channel When one of the parties starts speaking the associated amplifying channel has to open rapidly, even for a low speech level, so that even the beginning of the first word will not be lost. During short intervalsbetween words or sentences of the conversation it should not be possible for the direction of transmission of the amplifier to be automatically reversed due to reverberation or cross-talk between the loudspeaker and microphone in the other'room.
  • theloudspeaker It is desirable for theloudspeaker to reproduce the sound with adequate volume, for example, at the normal speech level, whereas at any instant the other-party should be able to interrupt .the first one andto reverse the direction of transmission of the amplifier without theneed for raising his voice markedly.
  • the reversal of the channels should be performed rapidly so that each party is able'to make a remark during the continuous flow of words of the other party without the beginning ofthe remark being suppressed due to inertia of the interchange.
  • the interchange of the channels should not give rise to instability.
  • a loudspeaker In general a loudspeaker is located nearer to the microphone than the person talking into it. When the loudspeaker reproduces the sound at speech level,-the associated microphone which, picks up the cross-talk signal can obviously provide a much stronger signalthan the microphone to which the direct speech signal is. applied.
  • the invention provides a; particularly efficacious solution of these problems.
  • the invention is characterized in that the speech signals from each channel are applied each through a first signal circuit to a first input of two comparison devices and the speech signals from each channel are furthermore each supplied through a second signal circuit to a second input of the two comparison devices.
  • the amplification of the first two signal circuits exceeds that of the second signal circuits and the comparison devices are designed so that they supply an output work signal when the signal level at the first input is higher than that at the second input.
  • the output signals are fed to an input of a first and a second gate circuit, respectively, in a third comparison device, while the outputs of the gate circuits are coupled with a second input of the other gate circuit in a manner such that, when a work signal is fed to one of the firstmentioned inputs of one of the gate circuits the other gate circuit is cut ofi".
  • the control voltages for the two control members are taken from the outputs of the gate circuits of the third comparison device.
  • the amplifier comprises two channels.
  • the speech signal of the microphone M is applied through the microphone preamplifier T,, auxiliary control member DR,, the control member R, and the output amplifier U, to the loudspeaker H,.
  • the other channel is arranged in an identical manner and comprises the preamplifier T,, auxiliary control member DR,, the control member R, and the output amplifier U
  • the auxiliary control members DR, and DR may be omitted since they are not essential to the invention. The purpose and function thereof will be described in detail below.
  • the microphone M, and the loudspeaker H are located in the same room, as are the microphone M, and the loudspeaker H,.
  • the speech signals for the control circuit are derived in the channels at points P, and P, preceding the control members R, and R,, respectively, so that these signals are not affected by the random states of the control members R, and R,
  • the signal at point P is applied through a first signal circuit including an amplifier FK,, a rectifier DA, and a delay device S, to the input A, of a voltage comparison device K,.
  • the signal at point P is applied similarly through the amplifier FK,, the rectifier DA, and the delay device S, to the input A, of a second comparison device K Moreover, the signals at points P, and P, are each applied through a second signal circuit including the amplifier FR,-and the rectifier D8,, and the amplifier PR, and the rectifier DB,, respectively, to a second input B and B,, respectively, of the comparison devices K, and K, respectively.
  • the comparison devices K, and K are arranged in known manner so that they supply an output work signal, for example, a high output voltage, when the signal level at their first input A, add A, respectively, exceeds by a given threshold value the level at the second inputs B, and B,, respectively.
  • an output work signal for example, a high output voltage
  • the outputs of the comparison devices K, and K are connected to the inputs C, and C, of the gates ND, and ND, of a third comparison device.
  • the outputs of the gates ND, and ND are each connected to a second input D, and D,, respectively, of the other gate and are furthermore connected via the junction points P and P, to the control members R, and R of the amplifying channels.
  • the gate circuits ND, and ND may be formed by Nand-circuits so that the output voltage is low only when the voltage at thetwoinputs is high. Thus, the voltage at the output is high whenthe voltage at just one of the inputs is low.
  • the control members R, and R are arranged so that when the voltage at the points P and P.,, respectively, is high, the control members are cut ofi or at least the amplification in the amplifying channels is so low that acoustic feedback cannot occur.
  • control voltages applied to the control members R, and R, provided that the arrangement as a whole continues performing the same function.
  • the signal levels at the various inputs of the comparison devices K, and K are proportional to the signals delivered by the corresponding microphones, independently of the state of the control members R, and R,.
  • the microphones do not deliver a voltage and the signal levels at the inputs of the comparison devices K, and K, are low (zero level) so that the voltage of A, is not higher than that of B, and that of A, is not higher than that of B,.
  • the voltages at the inputs C, and C, of the gates ND, and ND, will be low and the voltages at point P and P will be high.
  • the control members R, and R are then cut off.
  • the signal produced by the microphone is amplified by the amplifiers T,, FK, and FR, and rectified by the rectifiers DA, and DB, so that the signal level at the inputs A, and B, increases.
  • the delay device S is designed so that the rise in the voltage level at A, is substantially not delayed.
  • the voltage at the input C remains low, but that at the input A, exceeds that at the input B, so that a high voltage appears at both inputs C, and D, of the gate ND, and the voltage at point P, becomes low.
  • the amplifying channel between the microphone M, and the loudspeaker H is opened through the control member R,.
  • the loudspeaker H is located in the same room as the microphone M, and preferably is mounted in the same cabinet as the microphone so that the distance between these two elements is small. It is desirable for the sound signal delivered by the loudspeaker H, to be as high as possible, preferably at the normal speech level. Therefore, the microphone M, also receives a very strong sound signal which, owing to the nearness of the loudspeaker H,, may be many times stronger than the sound received by the microphone M,. In a practical case, as a result of the direct cross-talk between the loudspeaker H, and the microphone M, the strength of the signal at point P, may be times that of the signal atrpoint P,.
  • This cross-talk signal is amplified via the amplifiers T,, FR, and FK, and subsequent to rectification by the rectifiers DB, and DA, it is applied to the inputs B, and A, so that the signal level at these inputs rises.
  • the rise of the signal voltage at the inputs B, and A will take place somewhat later than at the inputs A, and B, and, more particularly, not before the voltage at point P, has become low.
  • the ratio between the amplification by the amplifiers PK, and F K, on the one hand and that by the amplifiers FR, and FR, on the other hand is chosen so that it slightly exceeds the ratio between the signals appearing at the points P, and P, when the microphone M, is talked into.
  • the signal amplification by the amplifiers FK, and FK may be 1 1 times that of the amplifiers FR, and FR,.
  • the signal at the input A will be much stronger (for example, more than 100 times in the present case) than the signal at point 8,.
  • the gate ND is closed and hence the signal at the input A, cannot have any effect or, in other terms, the amplifying channel between the microphone M, and the loudspeaker H, remains open and that between the microphone M, and the loudspeaker H, remains cutoff.
  • this situation must not vary, at least not as long as the other party at the microphone M, does not want to interrupt.
  • the signal at point P not only appears somewhat later than at point P, but also disappears somewhat later.
  • the delay device 8 which discharges comparatively slowly, the high signal level at the input A, is maintained for a short time after the signal at point P, has disappeared, i.e., for a time sufficient to insure that the signal at point P, also has decayed.
  • the party in the other room may interrupt the first one by supplying an adequate sound signal to the microphone M,. Owing to the combined effect of this sound signal and.
  • the signal level at the input B can rise above that at the input A,.
  • the voltage at the input C, of the gate ND drops so that a high voltage appears at point P resulting in the cut-off of the control member R,.
  • the voltages at the two inputs of the gate ND are now both high.
  • the point P then has a low voltage so that on the one hand the gate ND, is closed and on the other hand the control member R, opens the amplifying channel between the microphone M, and the loudspeaker H,,. This change-over is performed very smoothly.
  • the signal level at the input B initially was slightly lower than the signal level at the input A,. It is desirable for this difference to be as small as possible.
  • the microphone M requires only a little additional signal for causing the signal level at B, to exceed that of A, or, in other words, the speaker at the microphone M, need raise his voice only to a slight extent to gain access to the device by reversing the direction of transmission of the amplifier.
  • Cross-talk from the loudspeaker H, to the microphone M is in general comparatively intimately dependent upon frequency.
  • cross-talk will be strongest at frequencies appearing at the central region of the speech spectrum, for example, between 1,000 Hz and 1,500 Hz.
  • the ratio between the amplifications of PK, and FR can then be adjusted in the optimum case so that at frequencies at which cross-talk is a maximum the signal level at the input B, still is slightly lower than that at the input A,.
  • the level difference may then be considerably greater, which means that at these frequencies a comparatively strong signal has to be supplied to the microphone M, in order to cause the level at input B, to exceed that at A,. This is not desirable because it is quite possible that frequencies at which maximum cross-talk occurs are only weakly represented in the speech spectrum of the speaker.
  • frequency correction may be carried out in the amplifiers so that the transmission through the amplifier FK, exhibits the same frequency depen dence as the transmission of the signal through the control member R,, the amplifier U,, the loudspeaker H,, the microphone M,, the amplifier T, and the amplifier F R,.
  • a correction may be carried out, for example, only in the amplifiers FR, and FR, so that the amplification of the high and low frequencies exceeds that of the medium frequencies.
  • a correction may be carried out only in the amplifiers FK, and FK, so that the low and high frequencies are amplified to a lesser extend than the medium frequencies. Even a mixed correction in the four amplifiers is possible. By means of this frequency correction it may be achieved that despite cross-talk the speech level of the interrupting party at the microphone M, need exceed the level at the microphone by only a small amount, for example, by 5 db.
  • the cross-talk level will be high. This is only an imaginary disadvantage. There is also an advantage in that direct cross-talk exceeds by far indirect cross-talk due to reflections from nearby objects or echos in the room. The overall cross-talk is therefore a practically constant factor and exhibits very little dependence upon the incidental disposition of the loudspeaker microphone combination in the room. This permits an optimum adjustment of the amplifiers FK,, FR,, etc.
  • control members R and R may be adjusted so that they either completely cut off the amplifying channel or so that a small steady amplification is left. It has been found that the latter alternative is to be preferred because in that case the distance between the rest condition and the completely open condition of the channel is smaller so that the opening of a channel from the rest condition is performed more smoothly or, in other words, even if the strength of the first syllable spoken is comparatively low, the relevant amplifying channel is immediately opened so that no part of this syllable is clipped.
  • auxiliary damping or control members DR and DR may be included in the amplifying channels. These auxiliary control members are controlled by the voltages at points P and P that is to say by the control voltages which govern the control members in the other channel.
  • the damping members DR and DR are arranged so that they are conducting in the rest condition of the arrangement, that is to say, in the example described above, when there is a high voltage at the points P and P
  • the voltage at point P remains high so that the damping member DR continues to conduct.
  • the damping member DR completely cuts off the other amplifying channel.
  • a speech-controlled bidirectional amplifier comprising first and second amplifying channels each of which includes a transmission control member governed by a control voltage derived from the speech signals appearing in the two amplifying channels at control points preceding the control member of each channel, first and second comparison devices each having first and second inputs and designed so that they supply an output work signal when the signal level at the first input exceeds the signal level at the second input, means for applying the speech signals of each channel individually through a pair of first signal circuits to the first input of the two comparison devices and individually through a pair of second signal circuits to the second input of the two comparison devices, the amplification of the first two signal circuits being arranged to exceed that of the second two signal circuits, a third comparison device including first and second gate circuits each having first and second inputs, means for individually applying said output work signals to the first input of said first and second gate circuits respectively, means for coupling the output of each gate circuit with the second input of the other gate circuit in a manner such that a work signal applied to one of the first inputs of
  • An amplifier as claimed in claim 1 characterized in that the two first signal circuits each include a charging circuit for maintaining the signal voltages appearing at the first inputs of the first and second comparison members for a given time after the speech signal applied to the respective signal circuit has terminated.
  • control members are adjusted to a control level such that in the rest condition of the amplifier each channel is partially open and exhibits a relatively low amplification, each amplifying channel further including a second control member governed by the control voltage developed at the output of the gate circuit of the other channel so that when one channel is open in response to a speech signal the other channel is completely cut ofi.
  • a voice-operated bidirectional amplifier comprising first and second transmission channels including first and second transmission control members, respectively, each controlled by speech signals appearing at a control point in each channel that precedes the respective channel control member, first and second comparison devices each having first and second inputs and designed to compare the signal levels applied thereto so as to produce a first output signal when the signal level at the first input exceeds the signal level at the second input, a first pair of signal coupling circuits for individually coupling the speech signals at the control points of said first and second channels to the first input of said first and second comparison devices, respectively, a second pair of signal coupling circuits for individually coupling the speech signals at the control points of said first and second channels to the second input of said first and second comparison devices, respectively, a third comparison device including first and second gate circuits each having first and second inputs, means for coupling the output of said first and second comparison devices to the first input of said first and second gate circuits, respectively, means for coupling the output of the first gate circuit to the second input of the second gate circuit and to a control terminal of
  • An amplifier as claimed in claim 5 further comprising signal delay means connected in series with the first inputs of said first and second comparison devices.

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  • Engineering & Computer Science (AREA)
  • Signal Processing (AREA)
  • Circuit For Audible Band Transducer (AREA)
  • Interconnected Communication Systems, Intercoms, And Interphones (AREA)
  • Amplifiers (AREA)
US853881A 1968-08-29 1969-08-28 Speech-controlled bilateral amplifier Expired - Lifetime US3660603A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
NO336968A NO123134B (de) 1968-08-29

Publications (1)

Publication Number Publication Date
US3660603A true US3660603A (en) 1972-05-02

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Application Number Title Priority Date Filing Date
US853881A Expired - Lifetime US3660603A (en) 1968-08-29 1969-08-28 Speech-controlled bilateral amplifier

Country Status (8)

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US (1) US3660603A (de)
BE (1) BE738074A (de)
CH (1) CH499934A (de)
DK (1) DK132640C (de)
FR (1) FR2016608A1 (de)
GB (1) GB1250380A (de)
NL (1) NL6912967A (de)
SE (1) SE351350B (de)

Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3925618A (en) * 1974-05-02 1975-12-09 Nippon Telegraph & Telephone Voice switch circuits for use in loudspeaking telephone circuits
US3952166A (en) * 1973-10-18 1976-04-20 Nippon Telegraph And Telephone Public Corporation Loudspeaking telephone circuit
US3953676A (en) * 1974-12-12 1976-04-27 Northern Electric Company, Limited Digital control of a loudspeaking telephone system
US3963868A (en) * 1974-06-27 1976-06-15 Stromberg-Carlson Corporation Loudspeaking telephone hysteresis and ambient noise control
US3970786A (en) * 1974-06-27 1976-07-20 Stromberg-Carlson Corporation Loudspeaking telephone with improved receive sensitivity
US4025728A (en) * 1976-01-29 1977-05-24 Sava Jacobson Speaker telephone
US4028506A (en) * 1973-12-12 1977-06-07 Nippon Electric Company, Ltd. Maximum value tracing circuit for digitized voice signals
US4465902A (en) * 1982-10-08 1984-08-14 Zenith Electronics Corporation Digital space phone system
US4542263A (en) * 1984-03-07 1985-09-17 Oki Electric Industry Co., Ltd. Speech control circuit
US4980908A (en) * 1989-05-30 1990-12-25 Voicetek Corporation Voice-switched gain control for voice communication equipment connected to telephone lines
US5544242A (en) * 1993-05-25 1996-08-06 Exar Corporation Speakerphone with event driven control circuit

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB668858A (en) * 1949-04-29 1952-03-26 Telephone Mfg Co Ltd Improvements in and relating to electrical communication systems
US3075045A (en) * 1960-08-29 1963-01-22 Bell Telephone Labor Inc Speakerphone
US3113181A (en) * 1960-11-25 1963-12-03 Ericsson Telefon Ab L M Amplifier arrangement
DE1281499B (de) * 1966-03-23 1968-10-31 Siemens Ag Schaltungsanordnung fuer sprachgesteuerte Freisprechgeraete mit veraenderbarem Daempfungshub

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB668858A (en) * 1949-04-29 1952-03-26 Telephone Mfg Co Ltd Improvements in and relating to electrical communication systems
US3075045A (en) * 1960-08-29 1963-01-22 Bell Telephone Labor Inc Speakerphone
US3113181A (en) * 1960-11-25 1963-12-03 Ericsson Telefon Ab L M Amplifier arrangement
DE1281499B (de) * 1966-03-23 1968-10-31 Siemens Ag Schaltungsanordnung fuer sprachgesteuerte Freisprechgeraete mit veraenderbarem Daempfungshub

Cited By (11)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3952166A (en) * 1973-10-18 1976-04-20 Nippon Telegraph And Telephone Public Corporation Loudspeaking telephone circuit
US4028506A (en) * 1973-12-12 1977-06-07 Nippon Electric Company, Ltd. Maximum value tracing circuit for digitized voice signals
US3925618A (en) * 1974-05-02 1975-12-09 Nippon Telegraph & Telephone Voice switch circuits for use in loudspeaking telephone circuits
US3963868A (en) * 1974-06-27 1976-06-15 Stromberg-Carlson Corporation Loudspeaking telephone hysteresis and ambient noise control
US3970786A (en) * 1974-06-27 1976-07-20 Stromberg-Carlson Corporation Loudspeaking telephone with improved receive sensitivity
US3953676A (en) * 1974-12-12 1976-04-27 Northern Electric Company, Limited Digital control of a loudspeaking telephone system
US4025728A (en) * 1976-01-29 1977-05-24 Sava Jacobson Speaker telephone
US4465902A (en) * 1982-10-08 1984-08-14 Zenith Electronics Corporation Digital space phone system
US4542263A (en) * 1984-03-07 1985-09-17 Oki Electric Industry Co., Ltd. Speech control circuit
US4980908A (en) * 1989-05-30 1990-12-25 Voicetek Corporation Voice-switched gain control for voice communication equipment connected to telephone lines
US5544242A (en) * 1993-05-25 1996-08-06 Exar Corporation Speakerphone with event driven control circuit

Also Published As

Publication number Publication date
DE1942814A1 (de) 1970-05-06
NL6912967A (de) 1970-03-03
SE351350B (de) 1972-11-20
DK132640C (da) 1976-06-08
DK132640B (da) 1976-01-12
GB1250380A (de) 1971-10-20
BE738074A (de) 1970-02-27
DE1942814B2 (de) 1976-10-14
FR2016608A1 (de) 1970-05-08
CH499934A (de) 1970-11-30

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