Abstract: The present invention relates to a method and apparatus for adjusting the gain of an amplifier circuit. A gain control circuit compares the output of the amplifier with a reference voltage and adjusts a variable resistor, thereby altering the gain of the amplifier.

Abstract: An automatic gain control (AGC) algorithm is provided to the digital signal processor instructions of an audio processing unit of a multimedia multipoint server. The AGC algorithm operates to bring the power level of the audio signal of every active channel to within a fixed range. The AGC algorithm allows the use of non-calibrated microphones, corrects for long distance signal attenuation, and provides improved audio level reference for audio switching and audio level video switching. The AGC algorithm is structured into two steps: calibration and gain control. The calibration includes defining a noise threshold. Gain control includes first calculating a dynamic speech detection level. Second, with reference to the speech detection level, determining whether an incoming audio signal is a speech-based audio signal.

Abstract: In a method and an amplifier circuit for harmonic distortion suppression in hearing aids with signal-dependent gain control (AGC), a number of decay times of different length are prescribed for the gain control, and a switch is made between the decay times, and the selection of the respective decay time ensues dependent on a status change of the signal to be processed.

Abstract: A decoder capable of decoding audio signals encoded using analog noise reduction techniques, particularly Dolby SR, is implemented by means of digital signal processing. The typical decoding paradigm used by analog Dolby SR decoders is modified to overcome the problems caused by delay which is introduced by the digital implementation. A gain factor is factored out of the feedback transfer function and is placed in the forward signal path of each stage of the digital decoder. A single control circuit can then be used to generate coefficients which define transfer functions of each filter stage of the signal path. Linear interpolation techniques are used to limit the number of coefficient entries necessary to emulate the transfer function of an analog Dolby SR decoder. The digital decoder structure can be inverted to produce a digital encoder which is capable of implementing any noise reduction standard desired, including Dolby SR.

Abstract: The disclosed audio signal processing system produces an acoustic signal in a listening space and includes devices for generating a desired volume signal, a noise signal representative of ambient noise conditions in the listening space, and an audio signal. The system further includes a variable gain amplifier for amplifying the audio signal in response to a gain control signal and a device for generating the gain control signal in response to a volume control signal. The volume control signal is generated in response to the noise and desired volume signals so that the volume control signal increases in response to increases in the noise signal. The volume control signal increases at a rate of increase and the rate of increase decreases as the volume control signal increases.

Abstract: A circuit presented automatically controls sound level. Sudden peak signal levels are controlled with a fast time constant of response and the overall sound level is controlled with a slower time constant of response. The feature can be enabled or disabled by the user via a microprocessor responsive to a remote control.

Abstract: A sticky leveler utilizing a window detection technique to preserve the relatively small level changes of an audio signal. The sticky leveler includes a voltage controlled amplifier (VCA) and a sticky detector, where an input signal is received by the VCA for creating a variable gain path to the VCA output. The control output of the sticky detector is coupled to the VCA control input for controlling the VCA gain. The detection input of the sticky detector may be coupled to the input signal for generating a feedforward automatic gain control leveler. Alternatively the sticky detector may be coupled to the output signal of the VCA for generating a feedback automatic gain control leveler.

Abstract: A computer implemented voice recognition method and system for adjusting an input level to adjust the input signal amplitude level of spoken words to enhance voice recognition. A user is prompted with a word to speak into a microphone. The spoken word is converted into an analog electrical signal having an input signal amplitude level. A sound card then converts this analog signal to a digital stream of data. This input signal amplitude level is compared to a reference amplitude level. An adjustment to an input volume control is made with respect to the comparison to adjust the input signal amplitude level to approach the reference amplitude level. The invention also uses an iterative process for a set number of iterations to make the adjustment for the input signal amplitude level to approach the reference amplitude level.

Abstract: A hearing aid uses multiple compression feedback loops to minimize sound distortion includes a preamplifier network having an input connected to an input receiver, an output, and an automatically adjustable gain. The preamplifier network measures an output signal which is preferably a voltage and automatically adjusts the gain in response to the output signal. The hearing aid also includes an output drive network having an input connected to the preamplifier network output and an output connected to a load, such as a transducer. The output drive network has an automatically adjustable gain which is responsive to a measured signal at the output of the network. A volume control circuit may also be connected between the output of the preamplifier network and the input of the output drive network to permit the person wearing the hearing aid to adjust the output volume.

Abstract: A system and method for automatically controlling signal gain and minimizing distortion due to widely varying signal levels are disclosed. The method comprises the steps of calculating an initial gain factor from a source signal and gradually varying the initial gain factor to within a preselected band of allowable values when the source signal is above a preselected minimum level and the initial gain factor is above the preselected band. The circuit comprises means for calculating an initial gain factor from a source signal and means for gradually varying the initial gain factor to within a preselected band of allowable values when the source signal is above a preselected minimum level and the initial gain factor is above the preselected band. The method and circuit are particularly adept at processing audio signals carrying spoken words, the signals characterized by periods of silence between the words.

Abstract: A device for automatic sound control includes a detection circuit for supplying objective sound and/or noise measurements relating to an ambient sound volume, and a fuzzy logic control circuit for adjusting, in response to the ambient noise measurements sound transmission characteristics supplied by an acoustic device. The device includes a fuzzy logic conversion circuit which is arranged between the detection circuit and the control circuit and transforms the objective ambient noise measurements into subjective ambient noise measurements for performing said settings. The device can learn the personal settings defined by a listener. The device can also detect speech and perform specific settings.

Abstract: A cable television (CTV) system having an ad-insertion apparatus for automatically inserting commercial segments into program material under the control of cue tones transmitted by the program source. The system includes apparatus for normalizing the audio signal levels of the program and commercial materials so that the audio portion of the output signal being transmitted to subscribers will have a relatively uniform loudness. The same concept may be applied to video signals. Additionally, signals coming from several channels may be normalized with respect to each other using the same technique. One aspect involves normalization of the audio level of the commercial, based on measured levels of the program audio preceding the advertisement. In other variations, the program audio level is adjusted to match a preset audio level of an advertisement. In another aspect of the invention, the audio level adjustment is achieved by monitoring the deviation of an audio modulator.

Abstract: A sound reproduction apparatus for a vehicle comprises: a sound source for generating a sound signal; a sound reproduction portion for reproducing a sound from the sound signal into a compartment of the vehicle; a microphone, provided in the compartment, for detecting the sound transmitted in the compartment and environmental sound noise and for generating a sound detection signal; a detection portion for detecting a magnitude of the environmental sound noise by detecting a difference between magnitudes of the sound signal and the sound detection signal; and a volume control portion for effecting volume controlling of the sound signal according to the magnitude of the environmental sound noise from the detection portion. An equalizing portion substantially equalizing gains of signal paths of the sound signal and sound detection signal supplied to the detection portion in a substantially silent condition of the compartment is provided.

Abstract: An electronic audio device, such as a radio having an audio loudspeaker is described, as well as a method of operation of such a device. The device has an audio stage (6) having an audio output for providing an audio output signal, an acoustic transducer (12) coupled to the audio output for outputting an acoustic signal and a microphone element (13) acoustically coupled to the acoustic transducer to provide a feedback signal representative of the output of the acoustic transducer. A comparison circuit (15) compares parameters of the audio output signal and parameters of the feedback signal; and a control circuit (16, 24, 50) responsive to the comparison circuit controls the audio stage when a parameter of the feedback signal differs from that parameter of the audio output signal by a predetermined amount.

Abstract: This disclosure shows the solid state emulation of elements of a thermionic emission device amplifier which distinguish it from solid state amplifiers: the output impedance of transformer impedance with plate resistance, the transfer function coupling from the driver tube to the output tubes, the non-linearity of the output tubes, the compression created by the power supply droop, the inclusion of "fat" from the power supply, bias shifting of the input, and driving the input from a non-linear network. This disclosure also depicts advantageous features not found in tube amplifiers: a means for turning it down and maintaining the tone by maintaining the interrelationships within the amplifier and fat creation from the amplifier output and from external sources. This disclosure is based upon the novel use of controlled gain and controlled impedance means.

Abstract: A voltage controlled audio attenuator, of particular benefit in audio limiters, is created by configuring a nearly-balanced four-resistor bridge such that at least one of the branch resistors is implemented as a magnetoresistive element, located in a variable magnetic field, typically generated by a coil energized by current from an electronic driver which is made controllable from a DC control voltage, which is thus enabled to control the attenuation of the bridge. A suitable feedback processing circuit, receiving input from the bridge output and producing the DC control voltage in a predetermined dynamic relationship, forms the feedback branch of an automatic loop, thus the voltage-controlled attenuator is utilized as a key element of an audio limiter.

Abstract: Adaptive compressive gain and level dependent spectral shaping circuitry for a hearing aid include a microphone to produce an input signal and a plurality of channels connected to a common circuit output. Each channel has a preset frequency response. Each channel includes a filter with a preset frequency response to receive the input signal and to produce a filtered signal, a channel amplifier to amplify the filtered signal to produce a channel output signal, a threshold register to establish a channel threshold level, and a gain circuit. The gain circuit increases the gain of the channel amplifier when the channel output signal falls below the channel threshold level and decreases the gain of the channel amplifier when the channel output signal rises above the channel threshold level. A transducer produces sound in response to the signal passed by the common circuit output.

Abstract: A volume reservation apparatus of an audio system stores data corresponding to currently-produced volume of sound and volume reservation data corresponding to the volume preprogrammed by a user for calculating a difference between the data at the time of wake-up reservation to supply a stepper-motor driving pulse corresponding to the difference, so that the preprogammed volume of sound is produced at the time of reservation. Also, a volume reservation method is provided, thereby solving the inherent problem of unsatisfactory wake-up indication effect resulting from the supply of recently-set low volume at a preprogrammed wake-up time when the wake-up time is preprogrammed under low volume state or a sleep-time function is preprogrammed under low volume state prior to preprogramming the wake-up time.

Abstract: The invention provides an automatic level control circuit which restricts and outputs a large input voice level received from microphone without causing the large input voice level to saturate when a microphone is used in a sound generating device such as a ka-ra-o-ke set. An automatic level control circuit includes a first potential divider comprising an automatic level control circuit for restricting sound level. The first potential divider includes a first resistor and a first transistor, where one end terminal of the first resistor is connected to an input terminal. An amplifier is connected to a connection point of the first resistor and the first transistor of said first potential divider and a second potential divider is provided. The second potential divider includes a second resistor and a second transistor connected to an output terminal of said amplifier.

Abstract: The disclosed audio amplifier arrangement includes a first amplifier stage for influencing the signal strength of the received audio signal for at least part of the frequency spectrum of an audio signal received through an input. An output amplifier stage amplifies the signal influenced by the first amplifier stage. A detection present in the output amplifier stage detects overloads of the output amplifier stage (3). A control circuit causes, in response to the detection signal, an adjustment to be made of the influence caused by the first amplifier stage if the overload signalled by the detection signal transgresses a certain limit. This limit depends on the magnitude of the adjustment already carried out, so that the degree of overload corresponding to the limit increases when the extent of the adjustment increases.

Abstract: This invention comprises a system to compensate for the noise level inside a vehicle by measuring the music level and the noise level in the vehicle through the use of analog to digital conversion and adaptive digital filtering, including a sensing microphone in the vehicle cabin to measure both music and noise; preamplification and analog to digital (A/D) conversion of the microphone signal; A/D conversion of a stereo music signal; a pair of filters that use an adaptive algorithm such as the known Least Mean Squares ("LMS") method to extract the noise from the total cabin sound; an estimation of the masking effect of the noise on the music; an adaptive correction of the music loudness and, optionally, equalization to overcome the masking effect; digital to analog (D/A) conversion of the corrected music signal; and transmission of the corrected music signal to the audio system.

Abstract: This invention relates to an arrangement (1) for protecting transducer (3) which converts an electric signal into an acoustic or a mechanic signal against overload and destruction. The arrangement is connected to the electric terminals of the transducer (3) and changes the electric input signal under overload condition. A reference filter (6) connected with the electric input of the transducer provides a monitored signal x(t) related to the load of the transducer (3) to a controller (7). If the amplitude of the monitored signal x(t) exceeds an prescribed threshold value the controller (7) activates a feedback loop realized by the reference filter (6), multiplier (8) and summer (5). This invention provides an effective protection of the transducer with a minimum of elements by using the reference filter (6) as both a signal detector and a controlled attenuation element.

Abstract: In a reproducing device, e.g., in the portable tape player, the sound leakage from earphones is effectively avoided by directly detecting the signal level of medium to high frequency sounds at the earphone, and suppressing the signal level depending on the detected result thereof, so that the deterioration in sound quality is prevented and the sound leakage is effectively reduced.

Abstract: A reception volume limiting circuit includes a detecting section, an A/D conversion section, a control section, and a speech data calculating section. The detecting section performs detection/rectification and smoothing of a receiver driving AC signal and outputs a DC signal corresponding to the level of the receiver driving AC signal. The A/D conversion section converts the DC signal into a digital signal. The control section calculates a time average value by averaging the digital signal every predetermined time interval, adds the currently stored attenuation amount to the time average value, and compares the time average value with a predetermined threshold value representing a critical sound pressure for protection of listener's hearing.

Abstract: A control process and apparatus which automatically ensures adjustment of the volume of sound delivered by a sound reproduction source, such as a car radio, as a function of the ambient sound signals so that the user has the sensation of listening to an audio program which is maintained at the same sound level regardless of variations in disturbing noise level. The apparatus uses a microphone which picks up the ambient sound signals and employs computer circuitry operating under program control for determining the average level of the ambient sound signals; circuits are used which supply signals to the computer representing the level of the sound delivered by the sound reproduction source; under program control the computer determines the difference in level between the ambient sound signal and the delivered sound signal to obtain a result (S.sub.OM) representing the value of the user's listening comfort. This value (S.sub.

Abstract: This invention relates to an arrangement (14) for protecting a transducer (2) which converts an electric signal into an acoustic or a mechanic signal against overload and destruction. The arrangement is connected to the electric terminals of the transducer and changes the electric input signal under overload condition. This protection arrangement comprises a controller (15), a monitor (16) and an envelope detector (17). The monitor (16) provides a signal indicating the electric or mechanic load of the transducer (2). The peak value of the signal is anticipated by using a predictive filter in the envelope detector (17) or a delay element in the controller (15). If the predicted peak value exceeds an defined limit an attenuation element in the controller (15) is activated and the input signal is changed in time to prevent an overload of the transducer.

Abstract: An automated method for modifying a speech signal communicated over a telephone network by applying a gain factor in a telephone set before any side tone is added thereto. The gain factor is a function of a received signal indicative of the background noise at the location of the telephone set. The gain applied may be a function of both the background noise level and the original speech signal. Either a linear or a non-linear (e.g., compressed) amplification of the original speech signal may be performed, where a compressed amplification results in the higher level portions of the speech signal being amplified by a smaller gain factor than lower level portions. The speech signal may be separated into a plurality of subbands, each resultant subband signal being individually modified in accordance with the present invention.

Abstract: The invention relates to a sound reproduction system comprising a source of a sound signal in electrical form, a first filter group for dividing the signal derived from the sound signal source into several sound signals occurring in different frequency bands and an adjustable gain amplifier for each frequency band for amplifying the sound signal occurring in said frequency band. To take into account the noise existing in the environment of the sound reproduction system in the adjustment of the system, the system further comprises means for generating an electrical signal proportional to the background noise existing in the environment and means for adjusting the gain of the amplifiers in response to said electrical signal proportional to the background noise.

Abstract: An audio compressor using interactive layered time constants to create an easy to use compressor which self adapts to the program characteristics and provides a desirable and pleasing effect over a wide range of audio program material. The audio compressor includes an adaptable filter connected between an output signal path and a control feedback signal path of a voltage control amplifier. The adaptable filter comprises a first resistor-capacitor circuit connected to the output signal path and producing a charging/discharging voltage which is more dependent on a transient peak value of the audio signals and a second resistor-capacitor circuit working under the charging/discharging voltage of the first resistor/capacitor circuit for producing a charging/discharging voltage which is more dependent on an average value of the audio signals.

Abstract: A known technique to improve bass reproduction in loudspeakers is by boosting amplitude at low frequencies, but this can lead to an overload at high signal level. This can be prevented if the level is detected in order to decrease the amplitude boost. To detect the level in the relevant frequency region, a band or high pass filter before the detector is normally used, but this creates a delay in regulation, so that a high signal peak can introduce audible distortion. The described arrangement prevents this, as the signal is led through a variable band pass filter (10) and directly to the detector (8), which therefore receives the full signal. The arrangement operates such that the lower cut-off frequency of the band pass filter changes so that the lowest frequency range gets the highest attenuation.

Abstract: An apparatus for automatically controlling the sound volume of a sound producing apparatus based on ambient noise includes a microphone which detects the sound produced by the sound producing apparatus and ambient noise. Adaptive filters approximate, based on signals sent from the sound producing apparatus to speakers thereof, the characteristics of the sound components, relating to the sound produced by an individual speaker of the sound producing apparatus, which are received by the microphone. A subtractor subtracts the output of the adaptive filters from the output of the microphone to obtain a signal representing the ambient noise. The adaptive filters receive the signal representing the ambient noise and use this signal as a coefficient updating signal. A signal converter converts the signal representing ambient noise into an ambient noise level representing the volume of ambient noise.

Abstract: This invention comprises a system to compensate for the noise level inside a vehicle by measuring the music level and the noise level in the vehicle through the use of analog to digital conversion and adaptive digital filtering, including a sensing microphone in the vehicle cabin to measure both music and noise; preamplification and analog to digital (A/D) conversion of the microphone signal; A/D conversion of a stereo music signal; a pair of filters that use an adaptive algorithm such as the known Least Mean Squares ("LMS") method to extract the noise from the total cabin sound; an estimation of the masking effect of the noise on the music; an adaptive correction of the music loudness and, optionally, equalization to overcome the masking effect; digital to analog (D/A) conversion of the corrected music signal; and transmission of the corrected music signal to the audio system.

Abstract: An automatic volume control to prevent the listener from having an odd sensation is obtained with a plurality of conditions taken into considerations. A plurality of control rules required to infer using fuzzy logic a volume correcting value on the basis of frequency band component levels, L, M and H and a volume level V are stored beforehand in a volume correcting value inferring portion 13. The volume correcting value inferring portion 13 obtains inference results of the individual control rules on the basis of the individual frequency band component levels L, M, H input from a filter circuit 12 and the volume level input from an audio reproducing portion 14, obtains a weighted mean of the respective inference results as a volume correcting value Z, and inputs the volume correcting value to the audio reproducing portion 14 to automatically correct the volume.

Abstract: An improved audio mixing system. The system is not limited to one type of microphone and does not depend on separate sensing microphones to determine the background noise level. In addition, the active signal is not amplitude modulated by extraneous noise inputted through inactive microphones. The mixing system divides the system gain between a plurality of input channels. The mixing system periodically samples the channels and determines which channel is the dominant channel. In response to this determination, the gain of the dominant channel is increased and that of the other channels decreased.

Abstract: A circuit for controlling a reproduced volume level of an audio signal to a desired level includes a peak detector for detecting a peak amplitude level in the audio signal, a user operable control for generating a signal indicative of a desired amplitude level, a comparator for comparing the detected peak amplitude level in the audio signal with the desired amplitude level and for generating a comparison signal as a result of the comparison, and a voltage controlled amplifier coupled to the comparator for adjusting the peak amplitude level in the audio signal in dependence on the comparison signal. The output from the voltage controlled amplifier then has the desired level.

Abstract: An electronic volume varying apparatus for producing a controlling signal to control an electronic volume in response to pulses from a manually operable pulse generator, wherein it is prevented, when incorporated in a cassette deck or the like, that a listener is surprised with a great sound volume after cancellation of a muting mode. A muting judging section outputs a memory disabling signal when a muting-on signal is supplied thereto, and a memory enabling/disabling device is interposed between a pulse counting device and a memory device of a controlling section and stops its outputting of pulse count data from the pulse counting device to the memory device in response to the memory disabling signal from the muting judging section. A method and apparatus which can accurately detect an input pulse from a manually operable pulse generator as well as a pulse switch which eliminates inadvertent outputting of a pulse are also disclosed.

Abstract: An audio frequency compressing system for amplifying an input signal to produce a power output signal while removing high-level signals which could harm a listener. Gain control in the feedback path of an amplifier includes both a gain controller circuit for supplying a constant feedback impedance and a plurality of resistors which can be coupled to the gain controller circuit to increase or decrease the feedback impedance. Coupling of the resistors to the gain controller circuit is controlled by a feedback control circuit having both an automatic gain control circuit and a continuous high-level protection circuit.

Abstract: An audio system employs a microcontroller to supervise the operation of an audio system including a digitally controlled audio processor which controls at least a wideband and a narrowband gain for the audio signal. The narrowband gain may preferably comprise a bass boost to the audio signal. Clipping distortion of the audio signal is avoided by sensing clipping in a power amplifier and reducing the digital commands for the wideband gain and the narrowband gain according to a method which reduces narrowband gain in preference to the wideband gain. After the narrowband gain is reduced to a predetermined gain, the wideband gain may be reduced if clipping persists. When clipping ceases, the narrowband gain is likewise restored to its original gain in preference to restoring of the wideband gain.

Abstract: A single-channel circuit for a hearing aid for persons with an impaired hearing faculty has a pre-amplifier and an output amplifier, a microphone and an earphone, as well as a full-wave rectifier circuit for producing a control voltage for a voltage-dependent attenuator connected to the pre-amplifier. In order to allow a favorable speech audibility characteristic over the entire amplification range, a voltage-controlled filter is provided for a single-dependent change in the frequency response. The control input of the filter is connected to the rectifier circuit. The filter is connected to the rectifier circuit via a time function element.

Abstract: A personal subliminal messaging system includes a wide range linear subliminal modulator (43), a digital audio recording or play device (46), a microphone (51) to pick up the sound at the ear, and an earpiece (50) to deliver the subliminal message. The sound level at the user's ear is detected and measured. After risetime and decay conditioning of the varying dc control signal, the wide range linear modulator (43) uses this signal to control the level of the message to the earpiece (50). The user adjusts the system for a liminal of a subliminal level. The psychoacoustic phenomena of Post Masking is used to increase the integrity of the message in subliminal messaging systems.

Abstract: An audio amplifier circuit according to the present invention features an arrangement of a power line with a smoothing capacitor inserted as a power filter and a power line without such a smoothing capacitor. The audio amplifier circuit in which an input stage amplifier of a main amplifier is supplied with power via the former power line has a muting circuit for rapidly charging a negative feedback capacitor for generating negative feedback voltage to be fed back from the following stage of the main amplifier to the input stage amplifier up to a voltage level at which a pop sound is inhibited when the power is supplied and for rapidly discharging the negative feedback capacitor up to a reference operating voltage level when the voltage of the former power line with the smoothing capacitor exceeds a predetermined level, the voltage of the former power line being monitored after the power is supplied from a power supply.

Abstract: An arrangement for adjusting the volume of a played-back signal by a microprocessor from an audio system, in which the volume is increased incrementally by a pulse generator. The instantaneous level of volume is tested constantly to determine whether it is equal to or higher than an previously-stored threshold. Further increase in volume is inhibited after the threshold has been attained, so that the current volume level is retained independent of actuation of volume controls. By actuating a switch, the volume may be further increased even after the threshold has been exceeded.

Abstract: A loudness control circuit for an audio device used in a reproduction circuit for reproducing a music signal recorded on a recording medium comprises one or plural level detection circuits for detecting levels of signal components of low and high frequency regions of a reproduced signal and control circuits for controlling the levels of the signal components of low and high frequency regions of the reproduced signal in response to outputs of the level detection circuits. The level control is made in accordance with a sound-pressure level for each frequency region of a reproduced signal so that an optimum compensation of the level in response to the sound-pressure level becomes possible.

Abstract: An automatic sound volume controller for use with audio equipment mounted on a vehicle adapted that the level of an input audio signal and that of the noises coming inside the cabin in running state are detected, and the difference therebetween is obtained. By use of different gain levels reflecting the level difference, a direct sound signal and an effect sound signal are individually amplified for synthesis. This makes it possible to prevent the added effect sounds from being masked by the running noises because the level of the effect sound signal varies with the noises. As a result, the reproduced sounds supplemented by the effect sounds can be heard clearly while the vehicle is running. With the vehicle in stationary state, the effect sounds are kept from getting excessive, protecting the vehicle passengers from the unpleasant sensation conventionally associated with the apparatus of this kind.

Abstract: An on-vehicle automatic loudness control apparatus according to the present invention comprises a volume control circuit for receiving an audio signal from an audio signal source, the volume control circuit controlling an output level therefrom in accordance with a first signal supplied thereto; a level detecting unit for receiving the output level from volume control circuit, the level detector controlling an output level therefrom in accordance with a second signal supplied thereto, a noise detecting unit for detecting environmental noise in a passenger space of a car to output a noise signal in accordance with the environmental noise level; a relative level detecting circuit for comparing the output level from the level detector with the noise signal to output a third signal indicative of a relative magnitude between the output level from the level detector and the noise signal; and a control circuit for outputting the first signal and the second signal in accordance with the third signal.

Abstract: Microphones sample the sound output from the speakers of a sound amplification system. The resulting time domain analog signals undergo a Fast Fourier Transform which yields frequency domain signals representative of the intensities of the frequency bands which compose the sound. The intensities or levels of each band are compared to stored permissible level limits for each frequency band. Attenuators respond to signals indicative of band levels being exceeded by respectively attenuating the frequency bands to which they are tuned so the speaker output does not contain frequencies which exceed permissible limits. The time weighted permissible averages for each frequency are also integrated to provide for production of signals representative of the cumulative sound dosage.

Abstract: A novel and improved automatic gain control (AGC) circuit which is ideally suited for use with sound systems which are operated in a very large environment, such as a supermarket or auditorium. The preferred embodiment of the circuit comprises first and second input channels and a single output channel. The first input channel is a feedback signal provided by a microphone which is placed near one of the speakers of the sound system. The second input channel receives a music signal which is being played by the sound system. The output of the circuit is a music signal which has a constant ratio relative to the noise detected in the environment. Constant power ratio operation of the system is achieved through the use of logarithmic processing of the signals in each of the respective input channels. Control circuitry is provided to maintain the gain level of the system at a constant level during periods of time when no music is present on the second input channel.

Abstract: A digital automatic gain control system for maintaining a constant output level through attenuating or amplifying an input signal is disclosed.

Abstract: The specification discloses an audio signal level control system including a center-tapped photocell incorporated into an attenuator bridge. The cell elements are monitored while processing the audio signal, and a control circuit regulates the light-emitting device in the cell in response to the monitored bridge values. Preferably, log compression and filtering are performed within the control means. Also preferably, a tracking subtraction principle is used in both the audio and control paths to expand the control dynamic range.

Abstract: A sound mixing control system applicable to recording, broadcast and sound reinforcement systems. The gain provided for each input channel through the system is monitored, and whenever the sum of all the gains exceeds a threshold the overall gain is reduced to limit the sum of the gains to the threshold. Simultaneously the output level of the mixer is measured, and whenever the level would otherwise exceed a threshold the gains of the input channels are reduced in proportion to their individual levels to limit the output level to the desired maximum. Signals may be divided into multiple frequency bands, processed in parallel and recombined.