Abstract: A multiple band frequency response controller for use in audio applications, to precisely control and equalize audio system response. The frequency response controller shown will adjust response in ten octave bands. The unique feedback system used will generate response curves of increased smoothness and accuracy. In addition, the method shown will be readily adaptable to external control by analog or digital control signals.

Abstract: A combination radio and tape player is disclosed which includes a signal equalization selector wherein the audio program selection switches which select either an AM or FM radio mode or a tape player mode of operation also simultaneously select various different sets of stored control signals which implement predetermined audio signal equalization in accordance with the type of audio mode of operation (program) that was selected. This is accomplished by the use of a random access memory which stores three pluralities (sets) of control signals, each plurality of control signals corresponding to a predetermined desired equalization for either the AM, FM or tape player modes of operation of the combination radio and tape player. Manual controls are provided which allow selective adjustment of the equalization provided in any of the AM, FM or tape player modes of operation.

Abstract: An audio device comprises an equalizer circuit, a control circuit for controlling characteristics of volume, balance, bass and treble, control signals producing circuit which produces signals for controlling said characteristics and a reference voltage producing circuit which produces reference voltage for carrying out the characteristics controls, in which the control circuit is forcedly provided with bass and treble control signals having half values of the reference voltage upon operation of the equalizer circuit.

Abstract: A current transfer amplifier includes a voltage signal source for supplying a voltage signal to be amplified, a voltage/current converter for converting the voltage signal from the voltage signal source into a current signal proportional to the voltage signal, a tone control circuit of a current amplification type supplied with the current signal, a non-linear switching element interposed between the output of the voltage/current converter and the input of the tone control circuit to transmit the current signal therethrough, a variable resistor for receiving the current signal to produce a voltage signal proportional to the current signal.

Abstract: A digital gain control apparatus includes a digital control signal generator producing a plurality of serial-binary coded signals, a clock pulse signal and a strobe signal. A shift register is supplied with the plurality of serial-binary coded signals and the clock pulse signal from the digital control signal generator. A latch circuit is connected to the output of the shift register and is supplied with the strobe signal from the digital control signal generator to convert the plurality of serial-binary coded signals into a plurality of parallel-binary coded signals. A decoder is connected to the output of the latch circuit to produce a plurality of control signals from the plurality of parallel-binary coded signals. A function selector circuit and a volume adjusting circuit for the selected functions is also provided, each being controlled by the plurality of control signals. The shift register, latch circuit and volume adjusting circuit are formed in one chip-integrated circuit.

Abstract: A tone control circuit includes a variable gain amplifier circuit, a first mixer combining the variable gain amplifier output with a tone control circuit input and providing its output signal to the variable gain amplifier input, and a second mixer combining the outputs of the first mixer and variable gain amplifier. The mixers may be either adders or subtractors as long as the natural logarithm of the overall gain of the tone control circuit varies substantially linearly with changes in the feedback ratio of the variable gain amplifier.

Abstract: In a loudness control circuit, the output DC voltage of a first variable DC voltage source is applied to a first amplifier for increasing volume to vary the gain of the latter, and to first and second differential amplifiers, while the output DC voltages of second and third variable DC sources are applied to the first and second differential amplifiers to provide difference voltages, which the applied to second and third tone control amplifiers which amplify the low and high frequency ranges, respectively, to control the gains thereof, so that the components of the sound in the low and high frequency ranges are boosted, thus achieving the weighting.

Abstract: A method is provided for correcting errors in the overall reproduction characteristics of an audio system installed in a residence. The method may include the steps of generating a test signal as an input to the audio system and converting the resulting sound generated by the system and its room environment into stored data whose values are a function of the sound. This data is then transported from the residence of a processing center. At the processing center, the stored data is read and utilized to fix the characteristics of an equalizer such that when it is installed in an audio system, it will give the desired correction to the output thereof. Thereafter, the resulting equalizer is transported to the residence and installed in the audio system.

Abstract: A frequency selection circuit which is equivalent to an LCR series resonant circuit, though not provided with inductance and which can adjust resonant frequency, selectivity or quality factor Q and circuit impedance at resonance independently of one another, merely by adjusting resistance. The circuit comprises an operational amplifier connected to receive an input signal at its noninverting input, a band rejection filter connected to an output of the operational amplifier, a positive feedback resistor connected between an output of the band rejection filter and the noninverting input of the operational amplifier, and a voltage divider connected between the output of the band rejection filter and the output of the operational amplifier and connected at its output to an inverting input of the operational amplifier. The band rejection filter comprises a series combination of a first resistor and a first capacitor and a parallel combination of a second resistor and a second capacitor.

Abstract: An audio receiver or other electronic device having a number of controllable functions is provided with control apparatus in which mechanical parts have been substantially eliminated. An electrically controllable device is provided to control each function. Memory registers provide inputs to the electrically controllable devices. The controllable functions may be on-off, as for a particular signal source, or may be variable, as for volume, tuning and tone in a receiver. Input controls include a single level control for adjusting the levels of all of the variable functions, and switches to select the function to be adjusted. Control means such as a microprocessor scans the switches and level control for changes in level and/or functions selected and updates the memory registers accordingly. A display is provided of selected functions and level.

Abstract: A high frequency roll-off circuit for a gain stage including an amplifier having a feedback network together with a dual potentiometer comprising two serially connected gang operated resistors connected between the amplifier feedback port and through a capacitor to the amplifier output port, one of the resistors forming a volume control and the other resistor forming a high frequency roll-off control whereby at high volume settings, high frequency roll-off is automatically provided.

Abstract: A tone control arrangement is disclosed which is suitable for use in various sound reproducing instruments and in which the signal-to-noise ratio of the reproduced sound can be improved by controlling the frequency response of the audible signal with a variable d.c. voltage source. Frequency response control by a single d.c. control voltage is achieved by connecting in series and in order a first mixer, passive circuit network having a signal transmission characteristic determined by the desired frequency response of the output sound signal to be reproduced, a multiplier and a second mixer. The inverting inputs of the first and second mixers both receive the output of the multiplier, while the non-inverting input of the first mixer receives the input audio signal. The non-inverting input of the second mixer receives either the output of the first mixer or the input audio signal. Finally, the second input to the multiplier is provided by a variable d.c. voltage source.

Abstract: A pushbutton tunable radio having an integral audio graphic equalizer is disclosed. During a tuning mode of operation for the radio actuation of any of five presettable pushbuttons results in the selection of a predetermined radio channel frequency within the AM or FM band, and a five digit display is provided indicating the selected channel frequency. During an equalizer mode of operation caused by actuation an equalizer mode selecting pushbutton, the radio remains tuned to the previously selected radio channel, but the frequency indicating display is now replaced by an electronic display indicating the relative emphasis of a plurality of subbands for the corresponding audio signals produced in response to the received radio channel. In the equalizer mode, actuation of any of the presettable radio pushbuttons results in selecting a corresponding one of the audio subbands for adjustment of its relative emphasis.

Abstract: A tone control device for an audio equipment comprises a first mixer amplifier, at least one second mixer, a third mixer and at least one band rejection filter, which are operatively engaged with each other such that a center frequency, Q value and gain thereof can be independently controlled.

Abstract: A tone control circuit device including a plurality of bandpass filters connected in parallel with one another with each of the bandpass filters having a different center frequency and each being variable in order to vary the tone as in a graphic equalizer. In one embodiment, the output signals from the bandpass filters are coupled both to non-inverting input terminals of output and input signal summers. The input signal is coupled to another input of the input signal summer and the combined signals coupled to inputs of each of the bandpass filters and to a non-inverting terminal of the output signal summer. In another embodiment, plural characteristic circuits, each including a band-stop filter, are connected in parallel between input and output signal summers through a disclosed amplifier network. With this invention, a graphic equalizer tone control device can be constructed which is essentially free from noise and which has a very low distortion factor.

Abstract: A tone control circuit including an operational amplifier having (a) an input circuit or output circuit and (b) a feedback circuit where circuits (a) and (b) are symmetrically disposed with respect to a reference potential such as ground. Circuitry is also provided to compensate for load and/or feedback impedances. Further, circuitry is provided to reduce the number of switches and capacitors needed to vary the high and low cut-off frequencies of the tone control circuit.

Abstract: An audio signal transmission circuit comprising a first variable attenuator (i.e. volume controller) from which a level-adjusted audio signal is derived, a tone control circuit connected to the output of the first variable attenuator and supplying a tone-controlled audio signal to a loudspeaker, and a second variable attenuator connected between the tone control circuit and a record terminal and feeding the tone-controlled audio signal to the record terminal. The first and second variable attenuators are mechanically interlocked and arranged in such a way that the sum of their attenuating factors remains constant irrespective of any attenuating operation. At the record terminal there can be obtained the tone-controlled audio output signal with a substantially constant level (amplitude level), irrespective of the level adjusting operation of the signal to the loudspeaker.

Abstract: Improved circuitry for providing bass control in audio playback systems using feedback circuits wherein undesirable deviations in frequency response above the bass region exhibited by previously available Baxandall feedback circuits are substantially eliminated by utilizing, in a preferred embodiment, a voltage follower amplifier, such as an emitter-follower transistor circuit in association with a single capacitance in the bass control circuit, which eliminates the undesirable frequency response deviations at the mid-frequency and higher frequency ranges so that frequency response curves at all settings of the bass control substantially coincide above the bass region.

Abstract: Control panel arrangement for an audio equalizer features grouped horizontal and vertical slider controls for convenience in adjusting channel gain, bandwidth and frequency response.

Abstract: A tone control circuit using only one potentiometer to provide bass or treble control is described. An integrator and a differentiator are connected to the input of the circuit and their outputs to the two ends of the potentiometer. Electrical connection between the potentiometer and the input is also made to provide a flat frequency characteristic component in the output signal.

Abstract: A tone control circuit for stereophonic amplifiers, guitar amplifiers and the like is disclosed. The tone control circuit includes a bass circuit having a first variable resistor whose movable contact is connected to an output terminal of an amplifier circuit, two resistors equal in resistance connected respectively to two end terminals of the variable resistor, and a capacitor shunting the variable resistor. The tone control circuit also includes a treble circuit having a second variable resistor, a resistor, and a capacitor. The treble circuit is connected in parallel to the bass circuit in such a manner that the gain in a particular frequency range of the amplifier circuit can be changed by varying the resistances of the two variable resistors.

Abstract: Circuits for a high fidelity sound reproducing system which are suitable for providing treble, bass tone boost and cut functions. The audio input signal is utilized for producing a signal having the magnitude thereof frequency dependent. This frequency dependent signal is divided by a splitter circuit into feedback and feed forward signals and combined with the audio signal to either decrease or increase the magnitude of the audio signal appearing at an output thereof as a function of frequency. The ratio of feedback to feed forward signals produced by the splitter circuit is controlled by a direct current (DC) control voltage applied thereto. Because the control of the frequency dependent signals to vary the function of the circuit is accomplished elsewhere than in signal path of the audio signal the circuit is suitable for providing tone control remotely.

Abstract: An audio fidelity frequency equalizer system for use with audio fidelity sound equipment in order to frequency contour sound reproduction to obtain a desired listening environment. The frequency equalizer system of the present invention includes a plurality of potentiometer controls for adjusting the frequency output in each of the eleven major separate octave bands which cover a range from approximately 20 Hz to approximately 20,000 Hz. The frequency equalizer system of the present invention includes an operational amplifier with each of the aforementioned potentiometers connected across the equalizer in feedback relationship. Moreover, each of the potentiometers operate in conjunction with a unique resonance circuit in order to achieve the desired frequency adjustability of the octave bands.

Abstract: A compensating circuit has a frequency response curve into which can be introduced elevations or depressions of selected breadth at selected frequencies. The compensating circuit includes a plurality of tunable circuit stages associated with different frequency ranges. Each tunable circuit stage includes a resistor and an inductor connected in series with each other and to the rotor terminal of a differential capacitor having two stator terminals. The first stator terminals of the differential capacitors are connected to the first winding or windings of one or more differential transformers, while the second stator terminals of the differential capacitors are connected to the second winding or windings of the one or more differential transformers. The voltage induced across the one or more differential transformers is then employed to supplement the voltage which is being transmitted to the output resistor of the compensating circuit by the input transformer of the compensating circuit.

Abstract: In known audio equalization systems, full room equalization cannot be employed because it introduces undesirable transient effects during the growth stage of a sound field, especially in a large auditorium. The invention seeks to solve this problem by establishing an initial state of the equalizing system giving a reduced degree of equalization whenever a signal commences but which effects a transition to normal equalization within a time typically of the order of some tens of milliseconds.