| JPS5834810 | [Title of the device] Squelch circuit |
| US3755625A | 1973-08-28 | |||
| US3992584A | 1976-11-16 | |||
| US4090032A | 1978-05-16 | |||
| US4139731A | 1979-02-13 | |||
| US4149032A | 1979-04-10 |
| 1. | 1 A multiple input program active audio trans¬ mission system including: a) at least two program output means, each 5 to generate a system program input signal of varying frequency range in response to receipt of an input program; b) input signal channel means for at least • two of said program input means, each in 10 put signal channelmeans including: i) input program signal filter means adapted to receive a portion of said program input signal and modify the frequency thereof to provide a 15 filtered input signal; ii) input program signal rectifier means to receive said filtered input sig¬ nal and provide full wave rectifi cantion thereof to provide a full 20 wave rectified direct current input signal; iii) comparator means having first input means to receive said full wave rec¬ tified direct current input signal 25 and second input means to receive a summation signal which is a func¬ tion of full wave rectified direct current input signals from all input channels and adapted to compare said 30 full wave rectified direct current input signal with said summation signal and to provide a first com¬ parator output signal in responce to a first selected ratio between _ OM 15 said full wave rectified direct current input signal and said summation signal and to provide a second comparator signal in re¬ sponse to a second selected ratio between s.aid full wave rectified direct current input signal and said summation signal; iv) program switch means having a pro¬ gram signal input connected to said program input means and a program signal output with control means to transmit said program signal to said program switch output upon receipt of said first comparator signal and to terminate transmission of said program signal upon receipt of said second signal; c) summation means to receive a portion of the full wave rectified direct current signal from each of said input signal channels to provide said summation signal to be supplied to said comparator means; d) sound mixing means to receive program input signals to provide a selectively mixed audio output signal; e) means to transmit said audio output sig¬ nal to selected locations. , The invention of Claim 1 wherein said program signal filter means is adapted to provide an output having a slope of three decibels per octave in the output frequency range of 1000 cycles per second to 4000 cycles per second. , The invention of Claim 1 wherein said first input means to said comparator means includes jυREΛ r OMPI 16 attenuation means to selectively modify said full wave rectified direct current input signal. 4. The inveniton of Claim 1 wherein said second input means to said comparator means includes attenuation means to selectively modify said summation signal. "BUR _ O. |
- - . Multiple Program Audio System
My invention relates to multiple input audio systems, for example for public address or sound systems which are useful in large, meeting halls or in any application where multiple source inputs are necessary and where several microphones are used to provide inputs to the sound system output.
In most prior applications, access of the individual microphone circuits to the output are sound activated by signals provided to the indi¬ vidual microphones and include control means to determine which microphone inputs are provided access. It is important that the control means determine the level of signals received from each input, compensate for ambient ' noises, and access those inputs where real signals are provided.
Backgound Art
In some arrangements, the output level is co - pensated by the number of active inputs and in other instances no compensation is provided. One such arrangement is shown in a booklet entitled "Field Effect Transistor Projects" published by Motorola, Inc. (TM) Phoenix, Arizona, U.S.A. (1966). An arrangement where the output is modified by the number of active inputs is shown in U.S. Patent No. 3,814,856 - Dugan, wherein a sound rein¬ forcement system for a defined area is disclosed having a plurality of input channels and input signal sources. In this arrangement, the ambient noise level in the area served by the sound system is sensed to generate a reference signal in response
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2 to the ambient noise level which is used to control access of each of the input channels to the system. The disclosed system provides for each input channel to have a means to generate a direct current control signal proportional to the ambient noise which is then supplied to ' a comparator for a com¬ parison with the reference signal. In this arrange¬ ment, a feedback system is provided around the com- parator to maintain the access of the input channel to the output. The reference also provides an out¬ put system having a variable gain amplifier means where ' the gain is boosted inversely, proportional to the square root of the number of active inputs. It is satisfactory in many applications but requires continuous monitor for the ambient noise level for reference purposes so that devices in accordance with the reference are not useful where no accurate ambient noise level can be obtained. Furthermore, in Dugan, the reference signal bears no relation to the number of activated input channels.
Also Dugan ' provides an arrangement intended to boost the sum of all the active information channels by an amount proportional to the magnitude of the control signal, regardless of the number of active input channels.
Another prior art arrangement is shown in U.S. Patent No. 3,992,584, Dugan, .which discloses- a sound -reinforcement system with a plurality of inputs to an output channel, where the total gain of the system remains constant.
In the arrangement diclosed in U.S. Patent No. 3,992,584, the individual input channels are actuated by co-action between a reference signal which is proportional to the instantaneous sum of the alter¬ nating current signals generated by the active
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3 input channels. In addition, the alternating current signal is also filtered and rectified to provide a direct current reference signal to be compared with the filtered and rectified output signal of -each input channel to selectively acti¬ vate the input channel.
Disclosure of the Invention
It has been found that the use of the summed alternating current inputs for a reference signal leads to distortion in the syte output as a result of phase cancellation which occurs in the summation of the alternating current reference signals. The distortions are disturbing and adver- sely affect the effectiveness of the system.
Additionally, since the reference (U.S. Patent No.. 3,992,584) provides an arrangement where each input channel includes a control and where the channel attenuation is achieved by means of a re- ference signal, and a direct current signal genera ated from the output of the microphone in mixing the signals is significant since the attenuation of each input channel is responsive to the magnitude of the compared signal as opposed to a switched system. In many applications, the imbalance resulting from the summation of alternating current signals limits responsiveness of the input channel and causes distortion in the system output.
The foregoing systems present the problems of distortion, or "dead spots", in certain applications and are unsuitable in other applications.
My invention provides a program-operated sound system which provides means for detecting active microphones and gating the microphones with a vari- able threshold determined by a summation of the
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4 total input signals without the necessity of highly specialized and custom-designed equipment.
The present invention provides an arrangement where a weak voice or sound can activate a micro¬ phone so 1 ' θήg as the input signal exceeds a thresh- hold level determined as a direct current summation of all other sources and provides an arrangement which is sufficiently sensitive to accept soft speech without the previously encountered irrita¬ ting characteristics of intermittent transmission under marginal conditions.
Furthermore, the present invention provides arrangements where the sensitivity of the system is improved without the need for delicate adjustment. Furthermore, it has been found particularly useful to attenuate the output level directly in a switch system in accordance with the number of active input microphones. In accordance with the present invention, I provide a multiple source input sound amplifying an activation system including at least one first microphone means to generate first source input signal and at least one second microphone means to generate a second source input signal, an input channel means is provided for each microphone means, including source input signal filter means to re- cieve a source input signal and transmit a portion of the source input signal as a filtered input signal to full wave rectifier means to provide a full wave rectified direct current input signal of selected polarity, summing means to receive the direct current input signals from each of the input channel means and to provide a direct current reference signal proportional to the sum of a full wave rectified direct current source input signals
5 received by the summing means, input channel com¬ parator means for each input channel to receive and compare the reference signal with the full wave rectified direct current source signal of the input channel and ' having an output operable to provide a first control signal- in response to a first ratio between the reference signal and the direct current channel input source signal and a second control signal in response to a second ratio between the reference signal and the direct current channel in¬ put source signal, input signal amplifier means for each input channel to receive the source input signal from the microphone means to transmit an amplified source input singal to output amplifica¬ tion means, where the input signal amplifier means is operable in response to first control signal and inoperable in response to the second control signal, multiple channel output means including out- put signal summing -means adapted to receive the amplified source input signal from the input signal * amplifier means of each activated input channel and attenuator means to receive the output signal from the output signal summing means and having input means to receive the first and second control sig¬ nals from each of the input channel comparator means of each of the input channels where the attenuator means attenuates the output signal from the output signal summin-g means in response to the number of first signals received from the input channel com¬ parator means.
Various other arrangements within the scope of the present invention will occur to those skilled in the art upon reading the disclosure set forth hereinafter.
6 Brief* Description of the Figures
The invention is described with respect to the accompanying drawings wherein: Figure 1 is a simplified block diagram of one arrangement ' within the scope of the present inven t tion;
Figure 2 is an arrangement showing a portion of the block diagram of Figure 1 with a simplified block diagram of an input channel in accordance with the present invention;
Figure 3 is a detailed view of one input channel in accordance with the present invention; and Figure 4 is a chart showing a response curve in accordance with one feature of the present invention,
Figure 1 is an illustration of one arrangement in accordance with the present invention where twelve microphones M1---M12 are provided in associa¬ tion with twelve input channels C1-C12. It will be understood that various numbers of' input microphones and channels can be utilized in connection with the subject invention and, in fact, the number of channels can be more or less than twelve. The in¬ put channels are described hereinafter in somewhat more detail, but with reference to Figure 1, each input channel includes a program output P01---P012 connected to a program buss PB which provides the information signals amplified and transmitted in the output section as described hereinafter.
Each input channel C1-C12 further includes a reference output R01-R012 which provides a refer¬ ence signal as described hereinafter, to a mixing buss M where the signal from the mixing buss is summed in an amplifier 11 where the output signal
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7 from the summing amplifier 11 is transmitted to a reference buss B. A reference input RI1-RI12 is provided from mixing buss M to input a reference signal to each of the input channels C1-C12 as described ' hereinafter.
Finally, each input channel C1-C12 is pro¬ vided with an attenuation output A01-A012 which provides ' an attenuation signal to a digital attenuator 12 as discussed hereinafter and described more particularly in my copeήding application Serial No. filed of even date herewith.
As further shown in Figure 1, the program outputs are transmitted- to program buss PB by means of outputs P01-P012. A program output summing am¬ plifier 13, for example a quad-*-operational amplifier Fairchild NE5534N can be provided to supply the combined programs of input channels C1-C12 ' to digital attenuator 12, Inputs AOl-Aol2 from each of the input channels C1-C12 are supplied to atten¬ uator 12 where the signals received from input channels C1-C12 can be of the logic or 0 and 1 character. The combined program signal supplied by summing amplifier 13 is attenuated in response to the number of active input channels C1-C12 as described hereinafter and the output signal 14 is supplied to a second current summing amplifier 16 of the same character as current summing amplifier 13. The output 17 from current summing amplifier 16 is supplied through a variable resistor VRl to an amplifier 18 which then supplies the program to an output, for example a loud speaker 19, and to an output indicator to a volume unit meter 21 for monitoring the operation of the system, Referring now to Figure 2 which is an illus¬ tration showing the input channel Cl of Figure 1 in
8 more detail: '* and -' indicating the presence of channels C2 and C3 where the position of microphones Ml, M2 and M3 is likewise indicated, microphone Ml gener- ates an input signal to a pre-amplifier 26 supplied with voltage VI, for example +15 volts and voltage V2. for example -15 volts where it is understood that the device is provided with VI and V2 as an operational voltage where the output 27 from pre- amp 26 is supplied through the non-inverting input 28 (3) of an amplifier 28 which is supplied with voltage- VI and V2 as indicated. The inverting in¬ put 28 (2) of.amplifier 28 is activated by the in¬ put channel control means as described hereinafter. Output 27 from amplifier 26 is likewise sup¬ plied to the noninverting input 31 (13) of an operational amplifier 31, for example a Fairchild Model 4136, which is also powered by voltage VI and V2 as indicated, Operation amplifier 31 is provided with a gain control circuit 32, described hereina ter in more detail, connected to the inverting input 31 (14) of operational amplifier 31 and to the out¬ put 32 of amplifier 31 so that the operational am- plifier 31 performs as a bandpass filter.
As shown in Figure 4, it has been found that it is particularly advantageous to provide a band¬ pass filter operable in the frequency range of ten cycles per second to 5000 cycles per second. It has been found particularly advantageous to utilize a filter of the type shown in Figure 2 where the rise is three decibles per octive to the rollover fre¬ quency of 5000 cycles per second beyond which there is no particularly useful control information trans- mission.
Output 32 from filter 31 is then passed to a
9 rectifier 33, described hereinafter where the out¬ put from filter 31 is rectified to provide a full wave rectified current having a selected DC voltage. In accordance with one feature of the present invention, -the output 34 from rectifier 33 is sup¬ plied to a mixing amplifier 36 described hereinafter 36 described hereinafter and to the non-inverting input of an operational amplifier 37, for example a Fairchild Model 4136, supplied by voltage VI and V2 and adapted to act as a voltage comparator. Comparator 37 is also supplied with a reference voltage Rll, previously described, from the refer¬ ence buss B. An output protection diode 39 is pro- vided in output 38 from comparator 37 which is adapted tb, advantageously, provide a logic signal dependant upon the relative inputs from 34 and Rll. For example, the output can be 0 or 1 depending upon which signal predominates where the output signal 38 determines ultimately whether the input signal from microphone Ml is passed to the output mode. utput 38 from comparator.37 is supplied to the base 39 of a transistor Ql having an emitter connected through capacitor Cl to the noniήverting input of an operational amplifier 42, for example a Fairchild Model A 4136 provided as a buffer de¬ scribed in more detail hereinafter; transistor Ql, capacitor Cl, and variable resistor VRl are asso¬ ciated to establish a delay time before release in event of a signal change at the output 38 of comparator 37, Advantageously, transistor Ql and the associated elements Cl and VRl are located at the output of comparator 37 so that the full effect of a comparison is realized by capacitor Cl, where- as,, if transistor Ql and capacitor Cl were located elsewhere before comparator 37, comparison would
10 not be fully changed in response to a transmission generated signal. The response of the system is dependant on the discharge rate of capacitor Cl 5 which in turn is dependant on the resistance of VR5. The ' signal at output 43 is passed through a protection diode D2 and a resistor R42 to a light.* emitting diode 46 to indicate the presence of an operational signal at the output from
10 amplifier 42. The signal 47 from diode 46 is supplied to the cathode of a zenor diode 48 where the anode is connected to the anode of a diode 49 having is cathode connected to ground 22. The anode of diode 48 is also connected through a
15 resistor R3 to voltage V2 and by means of a connec¬ tor 51 to the gate of a field effect transistor Q2 having the drain connected to ground 22 and the source to input 28 (2) of operational amplifier 28.
20 Output 47 from light emitting diode 46 is also connected to lead A01 to a digital attenuator described hereinafter.
In operation, input channel 1, as -described above, is provided with a microphone Ml which
25 receives a signal where the input signal is pre- amplified by amplifier 26 and the program signal or input signal is provided to input 28 (3) of amplifier 28 and to filter 31 where the signal is refined and filtered. The output 32 from amplifier
30 31 is supplied through a rectifier 33 where the signal is rectified to provide a full wave filtered direct current signal which is supplied to one input of comparator 37, The other input of com¬ parator 37 is connected to lead Rll, a reference
35 input and when the signal at input 34 exceeds the reference signal of input Rll, a signal is provided
11. in output 38 for example a positive signal or a 1 signal, which is then supplied to the base of tran¬ sistor Ql to impose a like signal on amplifier 42, The signal is then transmitted to the digital attenuator " by means of lead A01 and to the field effect transistor Q2 which turns on amplifier 28 to transmit the program signal to the audio buss for transmission to the output, Referring to Figures 1 and 3, a master se¬ lector switch arrangement is shown to provide man¬ ual and automatic control of the input channel. A transistor Q3 is provided to act as an electronic switch to mute the normal signal 43 from amplifier 42. Associated switches A3 and A4 each having contacts Cl, C2 , C3 and C4 respectively are also provided. In position Pi, voltage VI is supplied to conduit 43 so the channel is activated by acti¬ vation of field effect transistor Q2 at the same time switch A4 contacts contact C3 to mute transis¬ tor Q3 to prevent transistor Q3 ' from muting the channel.
When switch A3 is in position P2, the chan¬ nel acts under automatic control. In this mode, switch A4 allows transistor Q3 to mute the channel shown when overridden by a signal from master selector buss 91,
When switch A3 and A4' are in position P3, transistor Q3 is muted so the signal from output 43 controls the channel shown as well as other channels connected to the master buss 91, A diode can be provided to prevent misoperation when more than one channel is in the master position.
Referring now to Figure 3 which illustrates in more detail the input channel shown in Figure 2, microphone Ml is provided in a transformer
12 coupled circuit through a transformer Tl where prea p 26 is shown having a gain feedback circuit including a resistor R3 to provide a fixed gain 5 for amplifier 26. Output 27 is then provided through a capacitor C3 to a variable resistor VRl, connected to ground 22, to adjust the output voltage 27A where output voltage 27A is then applied to input 23 of amplifier 28 and through
10 a capacitor C4 to input 31 (13) of amplifier 31. As shown, the gain of amplifier 31 is determined through a feedback circuit including resistors R4-R6 and capacitors C6, C4, C7 to provide the selected filter characteristics. Output 32 from
15 amplifier 31 is supplied, through a capacitor C8 to the input of rectifier 33 which includes oper¬ ational amplifiers 33A and 33B, for example Fair- child Model 4136, where amplifier 33A is connected through resistor R8 to input 32 while diodes 71 and
20 72 are. provided, as shown, for rectification where the non-inverting input of amplifier 33B in series through resistor 9 to the output 32 from amplifier 31, The non-inverting input of amplifier 33B is connected to ground 22 as shown. The output -34
25 fromrectifier 33 is connected through connector ROl to mixing buss M and to a variable resistor VR2 pro¬ vided in series with ground 22 and to adjust the input to comparator 37, As mentioned previously, the inverting input to comparator 37 is connected
30 by means of a lead Rll to reference buss B, A diode 81 is provided at the output from comparator 37 and is in series with the base of transistor Ql as previously described.
The balance of the circuit shown in Figure 3
35 is substantially identical to the input channel shown in Figure 1.
13 Referring again to Figure 1, program signal is supplied to program buss PB and supplied to summing amplifier 13, the output of which is supplied to digital attenuator 12. Each of the attenuator outputs A01-A012 from the input channel C1-C12 is supplied to digital attenuator. The total attenuation of the signal supplied from amplifier 13 increases with increasing numbers of active input channels and advantageously in direct proportion to the increasing strength of the signal received from amplifier . 13,
The output 14 from digital attenuator 12 is supplied for amplification and adjustment and final output by means of speaker 19,
It will be understood that other arrangements within the scope of the present invention will become obvious to those skilled in the art upon reading the foregoing disclosure of ;one example of one arrangement in accordance with the present invention.