Audio decompression system employing multi-rate signal analysis
First Claim
1. An audio decompression apparatus for generating a first time domain audio signal comprising a first set of time domain audio signal values from a plurality of sets of first frequency components, each said first frequency component representing the average amplitude of said time domain audio signal in a corresponding frequency band over a corresponding time period, said apparatus comprising:
- means for receiving a compressed audio signal comprising said sets of first frequency components, the number of frequency components in each said set being M;
synthesis means for generating M time domain audio signal values from each said received set of first frequency components, said synthesis means comprising means for generating 2M polyphase components from said set of first frequency components;
means for generating a W entry array from said polyphase phase components, and multiplying each entry in said array by a corresponding weight value derived from a prototype filter;
FIFO buffer means for storing said time domain audio signal values and for outputting the same to a D/A converter, said FIFO buffer means further comprising level indicator means for generating a signal indicative of the number of time domain audio signal values stored therein;
clock means for controlling the rate at which said FIFO buffer means outputs said time domain audio signal values; and
control means responsive to said level indicator means for causing said synthesis means to generate an approximation to said time domain audio signal values if said indicator means indicates that the number of time domain samples stored in said FIFO buffer means is less than a first predetermined value, said approximation requiring a lower number of computations than would be required to generate said time domain audio signal values.
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Abstract
An audio decompression system is disclosed. The corresponding compression system utilizes sub-band analysis filters whose bandwidths are chosen to approximate the critical bands of the human auditory system while avoiding the aliasing problems encountered in QMF filter banks designed to provide similar band splitting. One embodiment of the invention may be implemented on a digital computer. The computational requirements of the synthesis filters may be varied in response to the available computational resources of the computer, thereby allowing a single compressed audio signal to be played back in real time on a variety of platforms by trading off audio quality against available computational resources. Similar trade offs can be made in compressing an audio signal, thereby allowing a platform having limited computational capacity to compress a signal in real time.
145 Citations
5 Claims
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1. An audio decompression apparatus for generating a first time domain audio signal comprising a first set of time domain audio signal values from a plurality of sets of first frequency components, each said first frequency component representing the average amplitude of said time domain audio signal in a corresponding frequency band over a corresponding time period, said apparatus comprising:
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means for receiving a compressed audio signal comprising said sets of first frequency components, the number of frequency components in each said set being M; synthesis means for generating M time domain audio signal values from each said received set of first frequency components, said synthesis means comprising means for generating 2M polyphase components from said set of first frequency components;
means for generating a W entry array from said polyphase phase components, and multiplying each entry in said array by a corresponding weight value derived from a prototype filter;FIFO buffer means for storing said time domain audio signal values and for outputting the same to a D/A converter, said FIFO buffer means further comprising level indicator means for generating a signal indicative of the number of time domain audio signal values stored therein; clock means for controlling the rate at which said FIFO buffer means outputs said time domain audio signal values; and control means responsive to said level indicator means for causing said synthesis means to generate an approximation to said time domain audio signal values if said indicator means indicates that the number of time domain samples stored in said FIFO buffer means is less than a first predetermined value, said approximation requiring a lower number of computations than would be required to generate said time domain audio signal values. - View Dependent Claims (2, 3, 4, 5)
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Specification