Abstract: A signal processing system comprising components such as split-band perceptual coders can receive a peak amplitude limited input audio signal and can process the signal in such a manner that the processed signal preserves the apparent loudness of the input signal but is no longer peak-amplitude limited. In one embodiment, upsampling is used in estimating the resultant peak amplitude and gain factors established in response to the estimated peak amplitude are applied to one or more frequency subbands of the processed signal.

Abstract: The invention is a volume and tone control circuit for audio sets which will not distort a signal when the volume is adjusted to maximum regardless of the tone. The circuit has a volume control in the form of a variable resistor with an intermediate fixed terminal, one end connected to an input terminal, the other end grounded, and a movable contact connected to an output terminal; an attenuation circuit connected to said input terminal; and, a tone control circuit connected between the output of said attenuation circuit and the intermediate fixed terminal. The degree of attenuation of the attenuation circuit is set so that the maximum gain of the attenuation circuit and the tone control circuit does not exceed 1. The position of the intermediate fixed terminal is determined so that amplitude-versus-frequency characteristics of the output signal become flat when the movable contact of volume control is set to maximum.

Abstract: An acoustic characteristic correction device includes a section for setting a desired characteristic of a response characteristic in a reproduction system including a sound field, a section for outputting information of a measured characteristic of the response characteristic, a section for computing a correction characteristic for realizing the desired characteristic on the basis of the desired characteristic and the measured characteristic, and a section for imparting the computed correction characteristic to a sound signal to be reproduced. The device may further includes a display section for displaying the set desired characteristic, a section for controlling the level or frequency of the computed correction characteristic, a section for imparting a compensation characteristic to the correction characteristic. Results of measurement at plural points for plural measuring times may be stored and an average value of the results of measurement may be used as a measuring signal.

Abstract: Selected broadcast stations are stored in a memory and accessed using preset memory buttons on a radio receiver. Audio effects such as tone settings and sound-field simulations are adjusted for a selected broadcast station in accordance with the tastes of an operator of the receiver. The audio effects are stored for recall whenever the selected broadcast station is accessed through the memory preset.

Abstract: The length (or the number of taps) of an adaptive finite impulse response (AFIR) filter is continuously modified to produce optimal echo cancellation. In accordance with one illustrative embodiment, this modification is performed by increasing or decreasing the number of delayed samples which are used to generate an echo estimate. More specifically, the number of samples used to generate the echo estimate is determined by selecting a trial number of samples and operating the filter for a sufficient length of time to allow the tap weights in the filter to stabilize. The tap weights are then examined to determine whether the taps at the end on the filter contribute at least a first threshold amount to the echo estimate. If not, the number of samples used in the filter is reduced and the process repeated. If the taps at the end of the filter contribute more than a second threshold amount, the number of samples is increased and the process is repeated.

Abstract: A Voss-type electronic tone control circuit in which the output of an amplifier is connected to the circuit output. An input resistor interconnects the circuit input and the amplifier inverting input and a feedback resistor interconnects the amplifier output and inverting input. One end of a first resistor is switched between the circuit input and the amplifier output. A first capacitor is connected between the other end of the first resistor and ground. A second capacitor is connected between the other end of the first resistor and one end of a potentiometer, the other end of which is grounded. The potentiometer slider feeds the amplifier non-inverting input. The capacitance of the second capacitor is different from that of the first capacitor, which enables the resistance of the first resistor to be increased, and the resistance of the potentiometer to be reduced compared with a conventional circuit. Increasing the first resistor resistance reduces loading on the boost/cut switch.

Abstract: A tone reduction circuit for headsets designed to attenuate high frequency signals while permitting low frequency signals to pass undistorted. Input signal is supplied to a low-pass filter, a high-pass filter and an automatic gain control circuit (AGC). Outputs from both filters are input to a comparator, with the comparator output connected to the gain control input of the AGC. The AGC is configured to attenuate only the higher frequency signals. Thus, the comparator output controls gain imparted to the output signal produced by the AGC. The comparator output signals no gain in the automatic gain control circuit when low-pass filter output is greater than high-pass filter output, but when the high-pass filter output is greater than the low-pass filter output the comparator controls the automatic gain generator to attenuate the higher frequency input signal in proportion to the difference between high-pass filter output and low-pass filter output.

Abstract: A sound recording apparatus for use in video tape recorders, for equalizing a sound signal before the sound signal is recorded onto a recording medium includes an operational amplifier where the sound signal is inputted to its first input terminal, a feedback resistor connected to an output terminal and a second input terminal of the operational amplifier, and a simulated inductor circuit connected to the second input terminal of the operational amplifier. The simulated inductor circuit has a buffer where a predetermined bias is provided to its input. Between an output of the buffer and the second input terminal of the operational amplifier is connected an impedance network whose circuit constant is switched by a switch which operates according to a recording speed mode of the video tape recorder. This switching changes an equalizing characteristic of the amplifier.

Abstract: A vehicle radio having a microprocessor based control has bass and treble tone controls and a fade control to produce digital settings. A tone adjusting arrangement compensates for the effect of fade change on perceived tone or frequency response. Tables of compensation values stored in a ROM and addressed by fade settings are used to change the nominal tone settings. The tone setting combined with the compensation value provides an adjusted or compensated tone value to maintain a consistent tone when fade is adjusted.

Abstract: A tone control apparatus for a sound system processing audio signals of front and rear channels. By providing front and rear tone control means for independently effecting the tone control in both of the front and rear channels, it is possible to prevent the generation of distortions in the front acoustic output when the control for raising the rear bass level is effected. Also, a tone control balance between the front and rear channels in a vehicle cabin, for example, can be set appropriately.

Abstract: Tuner for receiving a plurality of receiving frequencies and audio system having a plurality of audio components, characterized by the provision of a device for generating a designation command for selectively designating a program source such as a broadcast station at the receiving frequency of the tuner or an audio component, and an equalizer for adjusting the audio signal from the selected program source to have a frequency characteristic according to the program source designated by the designation command. By this provision, the need of operating tone controls at each time of the change of program source is obviated, so that the readiness of operation is improved.

Abstract: An audio reproduction system for use in an audio amplifier, for example, has a tone control unit for increasing or reducing a gain, or keeping an increased or reduced gain, of a signal if a particular frequency range of an audio signal supplied thereto, and a volume control unit for increasing or reducing the gain of the audio signal in a full effective frequency range. The tone and volume control units are ganged by a gain control unit, so that the gain which has been increased in the particular frequency by the tone control unit, can be controlled depending on the degree to which the gain has been increased by the volume control unit. The tone and volume control units may include variable resistors, respectively, whose movable contacts are interconnected. When the knob of the volume control unit is shifted toward a higher scale level position, the gain of the signal in the particular frequency range is lowered by the tone control unit, thereby preventing the reproduced sound from being distorted.

Abstract: An automatic program synthesizer is disclosed.

Abstract: A tone control circuit having a first differential amplifier and a second differential amplifier. The first differential amplifier comprises first and second transistors whose emitters are connected. The second differential amplifier comprises third and fourth transistors whose emitters are connected. The base and collector of the third transistor are connected to the base of the second transistor and the collector of the first transistor, respectively. The base and collector of the fourth transistor are connected to the base of the first transistor and the collector of the second transistor, respectively. A demodulated signal is input to the differential amplifier, and also to the second different amplifier via a band-pass filter.

Abstract: A loudspeaker device comprises an input circuit for obtaining an input signal to be sounded by a loudspeaker as a digital signal, a phase correction circuit for correcting the digital signal in phase, a loudspeaker drive circuit for producing a loudspeaker drive signal in accordance with the digital signal which has been phase-corrected by the phase correction circuit, and loudspeakers driven by the loudspeaker drive signal. The phase correction circuit consists of a digital filter capable of determining sound pressure-frequency characteristics and frequency-phase characteristics independently from each other. By determining the two characteristics in such a manner that, for example, the sound pressure-frequency characteristics will become flat and the phase-frequency characteristics will become linear, naturalness in hearing can be improved.

Abstract: Apparatus and method for establishing and changing the volume level of a tone generator which may be used in connection with auditory feedback in a point of sale terminal or other business machine include a microprocessor having a timer with two settable registers which can be set to establish the duty cycle of a signal, an inverting buffer coupled to the timer output, an integrating circuit to which the signal from the buffer is applied, a transistor driver for a speaker to which the integrated signal is applied, and the speaker, the volume of the tone of which may be changed by altering the relative counts of the two timer registers.

Abstract: A signal processing circuit for hearing aids includes a broadband peak detector for generating a control voltage based upon the sound pressure level of an incoming acoustical signal over its entire frequency spectrum. The control signal is used to determine the cut-off frequency of a voltage controlled adaptive high-pass filter. An amplified electrical signal, corresponding to the acoustical signal, also is provided to the high-pass filter. In setting the cut-off frequency, the control voltage causes the high-pass filter to selectively suppress the low frequency portion of the signal, generating a modified signal in which the noise component is reduced.

Abstract: The complementary pre-processing and post-processing circuits of this inventiona re advantageous for reducing noise introduced into a signal by a process or medium where the noise introduced rises with the signal level. The pre-processing circuit analyzes the spectral composition of an input signal and generates an emphasis control signal to so indicate. The emphasis control signal is limited by a limitation circuit to a desired bandwidth. The pre-processing circuit includes an emphasis applying circuit for amplifying or attenuating the input signal as a function of the emphasis control signal. A delay circuit delays the input signal relative to the emphasis control signal so that the input signal reaches the emphasis applying circuit when the emphasis control signal is available for controlling the amplification or attenuation applied.The post-processing circuit restores the spectral composition of the signal.

Abstract: A microphone is provided with a read only memory (ROM) which is programmed to compensate for the microphone's nonlinear frequency response characteristic during their integration into a single unit. The ROM is thus programmed to provide a frequency response complementary to that exhibited by the microphone. The microphone may have a relatively poor frequency response over the audio spectrum, i.e., 20 Hz-20 kHz, but with the ROM serving to calibrate the microphone, the combination exhibits a relatively flat frequency response over this frequency range. Intended for use in a portable, battery operated, microprocessor-controlled audio spectrum analyzer, the integrated microphone and ROM combination is coupled to a CMOS random access memory (RAM) in which the calibration contents of the ROM are stored. During normal operation, the microprocessor reads the microphone calibration data from the thus programmed RAM in order to conserve battery power, but may read this data from the ROM when necessary.

Abstract: A tone control has a transfer function characterized by a zero and pole on the real axis spaced from the imaginary axis by an audible frequency with adjustment of a potentiometer causing one of the zero and pole to slide along the real axis while the other remains stationary. A treble control with fixed pole at 1 kHz from the imaginary axis has a potentiometer connected to an input terminal with its arm connected to an output terminal and is in series with a resistor and capacitor between the input terminal and ground. A bass cut control has a capacitor connected to an input terminal in series with a resistor between the input terminal and ground. The capacitor is shunted by a potentiometer having its arm connected to an output terminal. A treble tone control circuit with both cut and boost has a center tapped potentiometer with first and second opposed ends connected to + inputs of first and second operational amplifiers, each having a feedback connection with the - input.

Abstract: An exemplary embodiment includes a plurality of parallel signal channels coupled with a signal input transducer, such as a microphone or induction coil. Each of the signal channels includes a respective bandpass filter for selection of a different frequency band, a controlled-gain amplifier, controlled by a volume control potentiometer, circuits for non-linear signal processing, and a bandpass filter for the reduction of distortion components caused by the non-linear processing circuits. A summing amplifier combines the signal components from all channels and is connected via an amplifier to an output signal transducer. Space requirements and power consumption are reduced in such a multi-channel processing arrangement by implementing all of the filters as sampled-data analog circuits. As a result hearing aids are provided which can be worn on the head, e.g. behind the ear.

Abstract: Apparatus for reducing unmasked quantizing noise modulation in adapting differential digital coding systems. In the digital encoder low frequency signals are boosted in the presence of dominating high frequency signals that are controlling the quantizing step size. The decoder has complementary cutting of low frequency signals. Optionally, unmasked high frequency noise modulation is reduced by variable pre- and de-emphasis.

Abstract: An energy discriminator is employed in conjunction with an adaptive filter to control updating of the filter transfer function characteristic. Specifically, the discriminator is employed to distinguish whether any significant received far end energy is only partial band or whole band. If the received energy is partial band the adaptive filter is inhibited from updating the transfer function characteristic during intervals that such energy is being received. On the other hand, if the received energy is determined not to be partial band and, hence, is whole band, the filter is enabled to update the transfer function characteristic during intervals that such energy is being received.In a specific example, the discriminator is employed in an adaptive echo canceler to inhibit updating an echo path estimate being generated by an adaptive transversal filter when partial band energy is being received and enabling updating of the echo path estimate when whole band energy is being received.

Abstract: A tone control circuit is provided having several parallel channels each of which comprises an electronic potentiometer. In each of the channels is disposed a filtering element. Thus, for an output terminal common to the different channels, each of the channels comprises a filter comprising a series element corresponding to the series element of this channel and a parallel element corresponding to the series elements placed in parallel of the other channels. The present invention simplifies the construction of tone control circuits in the form of integrated circuits.