Abstract: An improved dynamics processing control system clamps a level detected control signal at a level equal to a predefined threshold point. In one embodiment, a clamped level detected signal feeds a filter with very slow response characteristics. By comparing the difference between the input and the output of the system a differential control signal generated. The differential control signal is used to provide a continuously variable, program dependant output signal when the input signal drops below a threshold point. In another embodiment of the invention, both the attack and release times of the system are varied in response to a differential control signal.

Abstract: A dynamically variable spectral matrix surround system decodes two-channel stereo into multi-channel surround. In one embodiment, the true stereo signal is present in left and right front and left and right surround channel outputs. When a dominant center channel signal appears, the system subtracts center channel audio from the critical voice band only. The higher frequency portion of the spectrum will remain true stereo at all times. In another embodiment, the front center signal bandwidth is determined. A dynamically variable portion of the audio spectrum is inverted and added to the opposite channel, thereby dynamically subtracting the bandwidth of the front center signal from the left front, left surround, right front and right surround channels but leaving the portion of the audio spectrum that does not contain front center information unaltered. The input is divided into two frequency bands.

Abstract: A multi-dimensional audio processor receives as an input either a single channel signal or a two channel signal from an audio signal source; for example a musical instrument or an audio mixer. The processor is programmable to divide the input among at least 3 output channels in a user-defined manner. The processor is also user programmable to provide a variety of effect and mixing functions for the output channel signals.

Abstract: A high output current negative feedback power amplifier amplifies an input signal by use of a monolithic operated amplifier with a current limiting resistor in its output path. The output current of the amplifier is automatically increased when the voltage drop across the current limiting resistor increases beyond a predetermined point and global current limiting automatically occurs when the output current of the monolithic amplifier exceeds a predetermined point.

Abstract: A matrix system encodes five discrete audio signals down to a two-channel stereo recording and decodes the recorded stereo signal into at least five stand alone, independent channels to allow placement of specific sounds at any one of 5 or more predetermined locations as individual, independent sound sources, thus producing a 5-2-5 matrix system. One embodiment of the system provides signals to left front, right front, center, left rear, and right rear speaker locations. The matrix system is compatible with all existing stereo materials and material encoded for use with other existing surround systems. Material specifically encoded for this system can be played back through any other existing decoding systems without producing undesirable results.

Abstract: An attack transient detector determines the moment of note onset; e.g. the time at which a guitar string is plucked; from a signal generated by a musical instrument. Detection of the attack transient causes the generation of a trigger signal which can be used to control processing of the musical instrument signal.

Abstract: A matrix system encodes five discrete audio signals down to a two-channel stereo recording and decodes the recorded stereo signal into at least five stand alone, independent channels to allow placement of specific sounds at any one of 5 or more predetermined locations as individual, independent sound sources, thus producing a 5-2-5 matrix system. One embodiment of the system provides signals to left front, right front, center, left rear, and right rear speaker locations. The matrix system is compatible with all existing stereo materials and material encoded for use with other existing surround systems. Material specifically encoded for this system can be played back through any other existing decoding systems without producing undesirable results.

Abstract: A differential input/differential output OTA includes two resistively degenerated matched pairs of bipolar transistors; one pair provides differential input, the other provides differential output and feedback to the first pair, thus canceling AC distortions. In voltage controlled filter applications that employ the new OTA, control feedthrough is significantly reduced when compared to similar low pass filters which employ conventional OTAs.

Abstract: An expandable multi-dimensional sound system has two modes of operation. Prior to the detection of a 20 kHz tone, the system is configured such that input audio panned hard to the left or right will result in the center and surround channels steering down so that the signal is only passed through the left front and right front channels, respectively. Mono information is fed only through the center channel, as the left and right front channels cancel any center channel or mono information. Material panned hard to the surround position steers down the front left and right channels and is only fed to the rear surround channels. No information is fed to the front center channel due to the fact that the signal contains only difference information. Directional steering to the rear channels is still provided in the absence of any hard broadband left or right panning. Upon the detection of a 20 kHz tone, the system is re-configured such that the left and right front channels and the center channel become disabled.

Abstract: An analog tape saturation simulator produces the same results as analog tape saturation in a controllable environment which can be user adjusted to the desirable level of saturation effect. A log-based audio detector receives the audio signal in front of a circuit limiting the maximum range over which a dynamic filter will operate to control the high frequency bandwidth via a voltage-controlled low pass filter which follows a soft-clipping distortion circuit also receiving the audio signal. The simulator provides dynamic changes to the signal based on the level of simulated saturation taking place. The simulator produces the nonlinear, soft clipping characteristics of overdriving analog tape and dynamically reduces the high frequency information in response to the input amplitude of the audio signal.

Abstract: In a dynamic noise reduction system, the release time versus frequency bandwidth is exponentially related and well beyond that achievable with a simple RC circuit.A dc control signal is derived from an input audio frequency signal by peak detecting the input signal, filtering the peak detected signal and controlling the release time of the filtered signal so that its release time is fast when the frequency is within a predetermined high range, its release time is moderate when the frequency is within a predetermined intermediate range and its release time is slow when the frequency is within a predetermined low range.

Abstract: A circuit automatically adjusts in response to an input audio signal to provide a dc control signal having the release characteristics of the input audio signal. The circuit has an input reference node for receiving a reference signal which is a function of the input signal, an output reference node for providing the dc control signal and an intermediate reference node between the input and output reference nodes. One or more diodes connected between the input and intermediate nodes permit forward conduction from the input node to the intermediate node. Components of a first signal path connected between the intermediate and output nodes provide a slow release time when the reference signal has a slow decay envelope.

Abstract: An audio sound system decodes from non-encoded two-channel stereo into at least four channel sound. The rear channel information is derived by taking a difference of left minus right and dividing that difference into a plurality of bands. In a simplistic implementation, at least one band is dynamically steered while the other band is unaltered so as to avoid any perceived pumping effects while providing transient information to left/right, as well as directional enhancement. In a preferred embodiment, multiple bands are dynamically steered left or right, so as to enhance directional information to the rear of the listener. In both schemes, the low pass filtered output of the sum of the left and right inputs is also combined with the directionally enhanced information, so as to provide a composite left rear and right rear output.

Abstract: An audio sound system decodes from non-encoded two-channel stereo into at least four channel sound. The rear channel information is derived by taking a difference of left minus right and dividing that difference into a plurality of bands. In a simplistic implementation, at least one band is dynamically steered while the other band is unaltered so as to avoid any perceived pumping effects while providing transient information to left/right, as well as directional enhancement. In a preferred embodiment, multiple bands are dynamically steered left or right, so as to enhance directional information to the rear of the listener. In both schemes, the low pass filtered output of the sum of the left and right inputs is also combined with the directionally enhanced information, so as to provide a composite left rear and right rear output.

Abstract: A preconditioned signal that is applied to the input of an audio power amplifier for providing a perceived control of reactance simulation (or the Damping Factor) of the amplifier. A low frequency fundamental resonance is combined with a slowly rising high frequency preemphasis to mimic or simulate an audible interaction with the impedance plot of the loudspeaker, without increasing the output impedance of the amplifier.

Abstract: A circuit for conditioning an input signal containing audio and noise components is provided in which a first circuit branch is used for deriving a first DC signal proportionate to the decibel level of high band information in the input signal and a second circuit branch is used for deriving a second DC signal proportionate to the amplitude of the input signal. A preselected maximum threshold reference is provided when the second DC signal drops below a preselected threshold and also for a predetermined time period when the second DC signal rises above the preselected threshold. The first DC signal and the maximum threshold reference are used to provide a peak detector signal input which is maintained at a level equal to the most negative level of the first DC signal when the maximum threshold reference is not provided and at a level equal to the most positive level of the first DC signal but not greater than the preselected maximum threshold reference when the maximum threshold reference is provided.

Abstract: A composite signal processor and single-ended noise reduction system uses a split input to the single-ended noise reduction circuit in such a manner that the audio signal from the output of the signal processor circuit is dynamically filtered in response to a control signal derived from the unaltered audio signal prior to signal processing. User selective switching is also provided to permit the signal processor and the noise reduction circuit to be used simultaneously or independently.

Abstract: A noise reduction system compresses an input signal at a constant ratio in response to a control signal derived from the compressed signal. Added to the derived control signal is a counterfeit control signal which causes the compressor to mistrack when the compressed signal falls below a preselected threshold level. Thus, low level compressor output signals are increasingly deemphasized. A constant counterfeit control signal produces a logarithmic decrease in compressor output signal levels below the threshold point. The resulting compressed signal is used to enhance system noise reduction. The input signal is fed to a filter having a variable bandwidth controlled by a signal derived from the compressed signal and responsive to compressed signal frequency and amplitude so that the filter is desensitized to input signal amplitude changes. A multistage filter control signal arrangement may be employed to provide variable cutoffs in more than one bandwidth.

Abstract: A system for the high gain amplification of musical audio signals uses a control signal derived from the audio signal to automatically vary the current in the gain control circuit of the amplifier in response to audio signal level changes. A distortion circuit in the feedback path of the amplifier provides controlled distortion. The system may also provide for a variable control signal threshold level and for variation in control signal decay characteristics. The system may further provide a user variable maximum gain control.

Abstract: An adjustable RMS circuit for an input signal is first compressed by use of a bipolar logarithmic converter. The low-level, high-frequency accuracy of the converter may be improved by increasing its gain in response to the presence of such components. An inverted half wave rectified signal derived from the compressed signal is then combined with a half intensity signal derived from the compressed signal to produce a signal which is substantially equal to the absolute value of the compressed signal. A reference signal of variably selectable level is further combined with the combined signal to provide an output signal offset to a desired threshold level.