AUDIO MIXER SYSTEM AND GAIN CIRCUIT THEREFOR

Abstract: An audio mixing system includes a control console (12), an audio signals mixer, and an interconnection mechanism for coupling said control console with said mixer using digital signal communications, the control console including a display (20) for displaying the values of selected parameters of said mixer, and a setting device for setting the values of respective displayed parameters as they are respectively displayed. A gain circuit for audio signals includes a differential amplifier (64) for amplifying a received balanced audio signal (68, 70) to produce an amplified output signal with respect to a reference signal level, a selectively operable pad circuit (60) for selectively attenuating such balanced audio signal input to said differential amplifier, a gain amplifier (64) for amplifying said amplified output signal to produce an amplified audio signal, a selectively operable impedance device (94) for establishing the effective gain of said gain amplifier, and a selector (80, 82; 96a, 96b) for selectively operating both said pad circuit and said selectively operable impedance device to cause such amplified audio signal to be at approximately a predetermined level.

Description: AUDIO MIXER SYSTEM AND GAIN CIRCUIT THEREFOR TECHNICAL FIELD This invention relates generally to audio mixers and to gain circuits for audio systems. BACKGROUND Typical prior audio mixers have received plural audio input signals; have provided for selective signal amplification or other alteration, such as phase, pan, and the like; and have been able selectively to mix respective audio signals to produce one or more audio output signals. Exemplary audio input signals may be derived or received from a microphone, an audio tape recorder, a video tape recorder and the like. The audio input signals usually are brought to a physically large console proximate which the operator sits and at which the audio signals are altered, mixed and used to derive one or more audio output signals, whether monaural or stereophonic. The audio input signals typically are produced at different respectve levels. For example, a signal received from a microphone may be as low as from about -16 db to about -20 db. On the other hand, a signal from a video tape recorder may be from about 10 db to 20 db. It would be desirable to amplify (either positively, i.e. to boost, or negatively, i.e. to reduce or to attenuate) the audio input signals to a nominal level of, say, 0 db so that effectively an equivalent control of each signal is possible, especially, according to the present invention, using generic control circuitry. By bringing all the audio signals to such nominal level, further signal level control of signals for mixing or other purposes would be facilitated. SUMMARY According to one aspect of the present invention, an audio mixer system in which a control console at which an operator may sit is separate from an audio rack at which audio signals are amplified, etc., mixed, and output. The audio signals are not generally transmitted to the control console. However, using digital signal coupling between the control console and the audio rack, which includes the actual audio • r_ * *.? '■ amp l ifying, etc. equipment, control of such equipment from the console and signal monitoring may be effected. A visual display and a plurality of programmable analog and digital controls coordinated with the information displayed may be used to set certain functions or parameters in the audio rack, such as initial amplification gain for achieving the nominal level mentioned above, which signals are to be selected for control and/or monitoring, which signals are to be mixed, and so on. An aspect of the invention relates to a selectable gain circuit capable of a relatively wide, say 40 db, amplification range. Such gain circuit may be used to provide selective amplification of an input audio signal to derive an amplified audio signal at a selected nominal level, say 0 db, that can be conveniently further amplified, mixed with one or more other audio signals, and so on. Thus, regardless of the db level of each input audio signal respective gain circuits in the audio system, the amplified audio signals will be at approximately the same nominal db level which will facilitate control of further amplification, mixing and other functions. The gain circuit includes a loss stage and a gain stage which are cooperatively adjustable to bring the input audio signal to the desired nominal level. Analog switches may be used to effect the selective adjustment of impedances coupled to such loss and gain stages to determine the degree of effective or overall amplification of the audio signal to achieve the desired nominal level. Signals from the control console selected by the operator determine the setting(s) of the analog switches (open or closed) according to a program or table relating desired gain to, for example, input audio signal level to achieve the desired nominal level. Another aspect of the invention relates to the time division multiplexing of the audio output signal(s) produced by the mixer at the audio rack to develop a bit stream carrying information concerning the amplitude level of each such signal. The bit stream is coupled over a pair of conductors to the control console for processing, e.g. decoding or reconstruction per signal, and display via conventional vu (volume unit) meters. The foregoing objects, aspects and advantages of the present invention will become more apparent as the following description proceeds. To the accomplishment of the foregoing and related ends, the invention, then, comprises the features hereinafter fully described in the specification and particularly pointed out in the claims, the following description and the annexed drawings setting forth in detail a certain illustrative embodiment of the invention, this being indicative, however, of but one of the various ways in which the principles of the invention may be employed. BRIEF DESCRIPTION OF THE DRAWING In the annexed drawing: Fig. 1 is a schematic block diagram of an audio system in accordance with the invention; and Fig. 2 is a schematic circuit diagram of a gain circuit useful, for example, in the audio system of Fig. 1. DESCRIPTION OF THE PREFERRED EMBODIMENT Referring, now, in detail to the drawing, wherein like reference numerals designate like parts in the several figures, an audio mixing system in accordance with the present invention is illustrated at 10 in Fig. 1. The fundamental components of the audio mixing system 10 include a control console 12, an audio rack 14, and interconnection facilities 16 for coupling the control console and audio rack. Importantly, the control console 12 and audio rack 14 are separate pieces of equipment, such separation being represented by the line 18. This separation permits the control console 12 and the audio rack 14 to be at different respective locations during use, while the interconnection facilities 16 permit communication and communicative operation between and of the two. Thus, for example, the audio rack 14 may be located quite close to the place where the audio signals are developed and mixed audio signals are used, and the control console 12 may be at a relatively remote (or proximate, if desired) location. Several advantages inure to such separation of parts. For example, since the audio signals do not have to be brought to the control console 12, signal attenuation and noise pick up problems are minimized. The amount of cabling to the remote location of the control console is minimized (relative to the number of cables required to bring all the audio signals to and from the control console) ; and the physical size of the control console may be relatively smaller than those in conventional audio mixing systems. The control console 12 includes a visual display 20, a number of programmable/programming analog and digital controls 22 directly associated with the visual display, a quick response control portion 24, an output level control 26, and a vu signal processing and display 28. The control console 12 may be physically located in a relatively small area in a control room separate from the area at which the audio rack 14 is located, e.g. the latter may be located directly at a sound stage, studio or the like. Direct communications between the control console 12 and the audio rack 14 preferably is by way of digital signals sent between the two on one or more signal carriers, busses, discrete wires or cables, etc. of the interconnection facilities 16. There also preferably is some degree of audio signal _ communication provided by the interconnection facilities 16 between the control console and audio rack, e.g. to permit the operator directly to monitor one or more audio signals. Desirably circuitry and programming information in the control console 12 causes the visual display 20 to display various information; and relying on the information currently displayed a user may manipulate one or more of the control buttons, knobs, etc. 22 to set relatively long term parameters of the audio system 10. For example, the controls 22 may be used to select two specific signals coming in to the audio rack to be mixed, one, say, from a microphone, and another. say, from a video tape recorder. Such signals may be received on pairs of lines 30, 32 as typical balanced audio signals, i.e. not referenced to ground, at the audio rack 14; and after appropriate operation performed on such signals the mixed audio output may be provided on one or more outputs 34, 36 of the audio rack 14. Such adjustment of signals, parameters, functions, and so on are considered relatively long term variables or settings because they ordinarily would be set at the beginning of an audio session or the like and usually would not be changed during the session. The display 20, controls 22 and associated circuitry also may be used to assign respective input audio signals, such as those received on lines 30, 32, to respective controllers or control strips 24a, 24b, etc. in the quick response portion 24. Thus, it will be appreciated that the coordinated useage of the visual display 20, controls 22 and associated circuitry permits the designating of a respective control strip 24a, 24b, etc. to act on a specified audio signal. Such coordinated functioning also may be used to assign specific audio signals for output at a specific master or auxiliary output channel. Each control strip 24a, 24b, etc. in the quick response portion 24 of the control console 12 may have a plurality of functions of the type typically available, for example, in conventional audio mixing systems. These may include level control, phase selection, pan balance control, "external input control (e.g. to send an audio signal to an external loop for usual purposes of signal delay or the like), filter control, muting, and the like. Such functions of the control strips are of the type that may require frequent or rapid change or adjustment during an audio session. Response to such changes or settings of the control strips 24a, etc. and of the display 20 and controls 22 may be placed in digital format and communicated digitally over the interconnection facilities 16 to the audio rack. There such information and control functions are decoded and acted on to effect the desired audio signal control, mixing and output signal(s) generation. To achieve such quick response of the control strips, each may include one or more potentiometric circuits, e.g. a potentiometer and an amplifier with appropriate coupling circuitry together with circuitry for digitizing the output thereof and coupling the digitized information to the audio rack via the interconnection facilities 16. Each also may include one or more buttons that may be pushed to mute or to unmute a signal, to determine the phase of the input audio signal, to couple in an external loop, etc., as generally is conventional in prior audio mixing systems but not in the separate console/rack environment of the present invention. The output level control 26 of the control console 12 may include respective potentiometric devices 26a, 26b, etc. and associated amplifier and digitizing equipment to determine the level of the mixed audio output signal delivered, for example on lines 34, 36 at the output of the audio rack 14. Additionally, in the control console 12 the vu processing and display 28 has a separate vu (volume unit) meter for displaying the level of each mixed audio output signal. The vu meters 28a, 28b, etc. , one for each mixed audio output signal, are conventional. The audio rack, though, contains processing circuitry 40 to effect time division multiplexing of representations of the mixed audio output signals, thereby producing a bit stream that can be reconstructed in the vu processor circuit 28' at the control console 12 for developing signals that can be displayed on the vu meters. An advantage of such multiplexed transmission of signals is that they can be sent over two wires without requiring a separate pair of wires for each output signal. Although the invention has been described in detail above with respect to two strip controls 24a, 24b, two output level controls 26a, 26b, two vu meters 28a, 28b, and two mixed audio outputs 34, 36, it will be appreciated that the invention comprehends circuitry that employs more than two of the foregoing and/or only one of the mixed audio outputs. depending on the number of signals to be handled and/or mixed by the audio mixing system and the number of outputs required. Turning to the audio rack 14 itself, the same may contain conventional amplifier, mixing and like circuitry that is operative to effect the desired level control, signal mixing and like functions. However, such circuitry is responsive to the digital inputs from the control console 12 as was described in further detail above. Importantly, the audio rack 14 includes plural gain circuits 50, 52 (and possibly more— referably one for each audio input signal that is to be provided simultaneous control by respective control strips 24a, 24b, etc.). Such gain circuits receive a balanced audio input signal from another device, such as a microphone, video or audio tape recorder, radio receiver, etc., for example on lines 30, 32. The actual balanced audio signal ordinarily is not referenced to ground. The balanced audio signal may be at various levels depending on the device at which it is derived; as was mentioned above, microphones typically produce low level signals whereas video tape recorders produce relatively high level signals. To facilitate the mixing and control of the such audio input signals the gain circuits can be selectively set, e.g. according to the visual display 20, controls 22 and associated circuitry in the control console 12, to amplify the balanced audio input signals to produce therefrom a nominal audio signal output, which is represented on lines ~ 54, 56. The signals on lines 54, 56 are provided the audio mixer 60 in the audio rack 14 for further amplification or level control, phase changing, pan balance adjust, mixing, and so on to develop the mixed audio output signals for delivery on outputs 34, 36. Turning, now, to Fig. 2, details of a representative gain circuit 50 are illustrated. The gain circuit includes two stages 60, 62, the former being a pure loss stage and the latter a pure gain stage. The loss stage 60 includes a differential amplifier 64. Across the differential input terminals to the amplifier 64 is an input resistor 66; and to such terminals also are coupled respective input circuits 68, 70. Each input circuit 68, 70 includes an input terminal 72, 74 across which the balanced audio input signal is received from another device, such as a microphone, tape recorder, etc.; a pad resistor 76, 78; and a selectively operable switch 80, 82 that may be opened or closed to determine whether or not the pad resistors are actively coupled in circuit with the amplifier 64 or are bypassed and, thus, out of the active circuit. The selectively operable switches 80, 82 preferably are analog switches of conventional design. In Fig. 2 such switches are represented as normally open contacts that can be selectively closed in response to an appropriate signal being sent to a relay coil or the like. Other types of electrical and electronic switches, such as relays, solenoids, electronic and/or solid state switches may be used for such purpose of bypassing or not the respective resistors generally in the manner shown in Fig. 2. In Fig. 2 an electrical line 84 is shown to provide a selection signal to a driving amplifier 86 that in turn provides a signal to a coil 88 that can operate the contacts 90 for such selective switching purpose. Preferably the line 84 is coupled to receive from the control console 12 a signal indicating whether or not the pad resistors 76, 78 are to be in or out of circuit with amplifier 64. According to the preferred embodiment and best mode of the present invention, the resistors 76, 78 are selected to be of a size that create a socalled -20 db pad. Therefore, when they are coupled in the circuit with amplifier 64, the output of the amplifier 64 is 20db less than the balanced input audio signal. In the case that the resistors are out of such circuit relation, i.e. the switches 80, 82 are closed, there would be no pad and the output level of the signal from the amplifier 64 would be about the same as that of the balanced input audio signal received on terminals 70, 72. A coupling resistor 92 couples the amplified signal output of the differential amplifier 64 to the input of the gain amplifier 93 in the gain stage 62. Also, coupled across the gain amplifier is a gain determining feedback circuit 94. The gain amplifier 93 may be an operational amplifier, and, as is well known, the gain of such an amplifier is a function of the impedances, such as the resistances, coupled thereto. Accordingly, the gain determining feedback circuit 94 includes plural resistors 94a, 94b, etc., preferably of different respective resistances, and plural analog switches 96a, 96b, etc. Such analog switches may be the same type as the analog switch 80 and may be selectively closed or opened according to control signals determined by the control console 12. Thus, each analog switch may include the illustrated contacts associated with a respective resistor, a coil, an amplifier, and an input terminal, as was described above with reference to the analog switch 80. According to the preferred embodiment and best mode of the present invention, the resistors in the feedback circuit 94 are of a size that allows the gain of the gain stage 62 to be varied select over a 20 db range at approximately equal increments. Moreover, and importantly, the loss stage 60 and gain stage 62 should be coordinated such that when the gain stage has 0 gain, the pad circuit loss stage has the ability to attenuate the the largest expected level of balanced audio input signal to the nominal level of, say, a θ db level. On the other hand, the maximum gain of the gain stage 62 should be of a size that will amplify a minimum level of received balanced input audio signal to the desired nominal 0 db level. Further coordinated operation of the gain and loss stages 60, 62 will be quite evident to bring the level of the received balanced input audio signal to relatively closely approximate the desired nominal level of, say, 0 db. Such coordination of selection would be included in programming of operation of the gain circuit, control console and/or audio rack, which is preferred, may be in a look up table for selection by the operator or automatic selection by the circuitry when the " " 10 operator indicates to the control console at the display 20 and button controls 22 the type of input signal (and possibly the usual level thereof) , as is evident according to known principles. For example, when a microphone signal is recieved at -16 db, loss stage would bypass the pad resistors, and the gain stage would amplify the signal by about 16 db to achieve the nominal level. If a 16 db signal were received from a tape recorder, the pad resistors would effect a -20 db pad being coupled in the loss stage, to produce a -4 db signal at the output of the differential amplifier 64, and the gain stage would amplify such signal by about 4 db to achieve the nominal level. In view of the foregoing, it will be appreciated that the present invention may be used to amplify signals to achieve the desired signal levels in a convenient manner and such s-ignals, especially when of the audio type, may be conveniently mixed, amplified, etc.

Claims: CLAIMS 1. A gain circuit for audio signals, comprising differential amplifier means for amplifying a received balanced audio signal, to produce an amplified output signal with respect to a reference signal level, selectively operable pad means for selectively attenuating such balanced audio signal input to said differential amplifier means, gain amplifier means for amplifying said amplified output signal to produce an amplified audio signal, selectively operable impedance means for establishing the effective gain of said gain amplifier means, and selector means for selectively operating both said pad means and said selectively operable impedance means to cause such amplified audio signal to be at approximately a predetermined level. 2. The circuit of claim 1, said selector means being operable to select said pad means and impedance means to produce such amplified output signal at O db. 3. An audio mixing system comprising a control console, an audio signals mixer, and interconnection means for coupling said control console with said mixer, said control console including display means for displaying the values of selected parameters of said . mixer, and setting means for setting the values -of respective displayed parameters as they are respectively displayed. 4. The system of claim 3, further comprising input means for receiving plural audio signals, said mixer including means for altering selected audio signals, and said control console including means for determining such altering. 5. The system of claim 4, said means for altering comprising a respective gain circuit for each of plural audio input signals. 6. The system of claim 5, comprising differential amplifier means for amplifying a received balanced audio signal, to produce an amplified output signal 12 with respect to a reference signal level, selectively operable pad means for selectively attenuating such balanced audio signal input to said differential amplifier means, gain amplifier means for amplifying said amplified output signal to produce an amplified audio signal, selectively operable impedance means for establishing the effective gain of said gain amplifier means, and selector means for selectively operating both said pad means and said selectively operable impedance means to cause such amplified audio signal to be at approximately a predetermined level. 7. The system of claim 3, further comprising means cooperative with said display means for establishing which of plural audio input signals are to be mixed by said mixer. 8. The system of claim 3, further comprising multiplexer means for receiving audio output signals and for producing a bit stream representative thereof, processing means for decoding such bit stream, and meter means responsive to such decoded bit stream for displaying the level of respective audio outputs. 9. The system of claim 8, further comprising a single pair of conductors for transmitting such bit stream between said multiplexer and said processing means. 10. The system of claim 8, said multiplexer means comprising plural vu meters. "" " * " r

Inventors: JUHASZ JOHN E, KAGEFF DANIEL, JUHASZ, JOHN, E., KAGEFF, DANIEL
Applicants: ORION RESEARCH, ORION RESEARCH, INC.
Application year: 1987
Main classification: H03G3
IPC codes: H03G3, H04H60