Teledyne Industries, Inc.

Teledyne Limited

Dolby Laboratories Corporation

Robert A Berkovitz

Kenneth James Gundry

Ronald P Genereux

James M Kates

This disclosure concerns an equalizer for an audio reproduction system in which equalization is achieved using a discrete time filter. The filter is preferably implemented with a microprocessor programmed for generating and storing the filter coefficients in accordance with a perceived acoustic test signal reproduced by the system. Following generation and storage of the coefficients, the microprocessor also serves to equalize an input audio signal by convolving the stored coefficients with digitized time samples of the audio input signal.

Automatic time domain equalization of audio signals

Variations in the amplitude-frequency response characteristic of a loudspeaker are compensated by a drive circuit in which an audio input signal is summed with a plurality of delayed replicas of the input signal to provide a drive signal for the loudspeaker. The delayed replicas are derived by discrete time filtering. Noise reduction techniques applied to the least delayed of the plurality of delay signals substantially improves the S/N ratio in the drive signal.

Loudspeaker system equalization

A sound reproduction arrangement and audio signal delay apparatus suitable for use in such an arrangement, includes, in a listening area, one or more primary sound sources for mono- or multichannel reproduction respectively, and a plurality of secondary sources spaced around the perimeter of the listening area and each providing an acoustic signal corresponding to that from the primary source or sources delayed by a respective and independently selectable delay constant and attenuated by a respective and independently selectable gain constant. Control apparatus is connected with the sound sources to derive a plurality of signals for the respective sound sources from an input signal. The delay constants are substantially greater than the time taken for sound to traverse the listening area, so that the sound from the secondary sources simulates reverberation or reflected sound, and a listener has a sensation of spaciousness normally associated with an enclosure which is larger than the listening area, such as a concert hall, for example. Features of the invention include a random-access memory which stores time-multiplexed data representing sampled input audio and channel-control information.

Stereo and spaciousness reverberation system using random access memory

A network is described which processes two channel stereophonic sound programs for playback through left, right and center sound reproduction channels. Use of the network allows certain advantages of a three channel program to be obtained from the two channel program. The network delays the left and right channels to give precedence to the center channel information but reduces the level of this information to enable the left and right channels to establish a stereo image.

Stereophonic sound system particularly useful in a cinema auditorium

A filter network for use with an acoustic signal reproduction system having at least two, spatially separable, speaker means each capable of reproducing acoustic waves from corresponding electrical signal. The network includes a frequency divider for separating an electrical signal representative of acoustic waves into first and second components, the first component including primarily those audio frequencies, which when acoustically reproduced tend to provide unambiguous binaural phase localization. The second component includes primarily those audio frequencies which when acoustically reproduced tend not to provide unambiguous binaural phase localization. The network also includes structure for delaying the first component for a predetermined period of time to produce a delayed signal so that when the combined first and second components are applied to one of the speaker means and the combined second component and the delayed signal are applied to the other of the speaker means the acoustic field produced tends to simulate spaciousness or ambience of a larger room than the actual listening area.

Auditorium simulator economizes on delay line bandwidth

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.

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Lexington, MA, United States of America

Robert A Berkovitz