Data compression method and apparatus
First Claim
1. In a data reduction system of the type for preparing varying average energy level analog input signals for storage or transmission, the combination comprisinganalog to digital converter means for converting the analog input signal to equal length digital sample signals,digital compression filter means responsive to digital sample signals from said analog to digital converter means for generating a stream of equal length compressed signals,digital encoding means implementing a truncated variable word length code for encoding the compressed signals from said digital compression filter means,entropy setting means for controlling the entropy of signals supplied to said digital compression filter means to control the entropy of signals from the compression filter,mode control means for obtaining a measure of the average energy level of the input signal prior to encoding by said digital encoding means and for producing an output indicative of an energy level band within which said signal falls, there being a plurality of different energy level bands ranging from low to high energy levels through which said signal may operate, andmeans for controlling the entropy setting means in response to the output from the mode control means for step control thereof with energy level band changes, the entropy of signals supplied to the digital compression filter means being reduced by said entropy setting means with changes from a lower to a higher energy level band and being increased with changes from a higher to a lower energy level band, the ratio σ
- /q being changed by a factor of 2x with each change in energy level band, wherein σ
is standard deviation of the compressed signal stream from the digital compression filter means, q is quantization level of the digital sample signals, and x is a non-zero integer.
1 Assignment
0 Petitions
Accused Products
Abstract
A music data compression system is disclosed which includes an analog to digital converter for converting the analog music signal to digital sample signal form, a digital compression filter for compression filtering the digital sample signals, and an encoder for truncated Huffman encoding the compression filter output. An entropy setting unit is included in the system for step control of the signal supplied to the digital compression filter in accordance with one or more threshold levels of the envelope of the music signal, and for reducing the entropy of the signal with increases in the energy level of the music signal. Different codes may be implemented in accordance with the threshold(s), and an identifying code word is inserted in the Huffman encoded stream. A decoder, digital reconstruction filter, and digital to analog converter are used to reconstruct the analog music signal. The identifying code word in the encoded signal stream to the decoder is used to select the necessary algorithm for decoding, and an entropy setting unit is included for step control of the gain of the digital reconstruction filter output under control of the identifying code word when step gain control is included prior to compression filtering.
171 Citations
44 Claims
-
1. In a data reduction system of the type for preparing varying average energy level analog input signals for storage or transmission, the combination comprising
analog to digital converter means for converting the analog input signal to equal length digital sample signals, digital compression filter means responsive to digital sample signals from said analog to digital converter means for generating a stream of equal length compressed signals, digital encoding means implementing a truncated variable word length code for encoding the compressed signals from said digital compression filter means, entropy setting means for controlling the entropy of signals supplied to said digital compression filter means to control the entropy of signals from the compression filter, mode control means for obtaining a measure of the average energy level of the input signal prior to encoding by said digital encoding means and for producing an output indicative of an energy level band within which said signal falls, there being a plurality of different energy level bands ranging from low to high energy levels through which said signal may operate, and means for controlling the entropy setting means in response to the output from the mode control means for step control thereof with energy level band changes, the entropy of signals supplied to the digital compression filter means being reduced by said entropy setting means with changes from a lower to a higher energy level band and being increased with changes from a higher to a lower energy level band, the ratio σ - /q being changed by a factor of 2x with each change in energy level band, wherein σ
is standard deviation of the compressed signal stream from the digital compression filter means, q is quantization level of the digital sample signals, and x is a non-zero integer. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19)
- /q being changed by a factor of 2x with each change in energy level band, wherein σ
-
20. Digital decoding and decompression means for producing digital signals fn (out) from a stream of encoded digital compressed signals, different portions of said stream having been encoded using different codes, said stream including an identifying code word at the start of each portion of the stream encoded using a different code, said digital decoder and decompression means comprising,
code checker and stripper means for stripping the identifying code word from the stream of encoded compressed signals and for producing a code identification signal corresponding to said identifying code word, digital decoder means responsive to the encoded compressed signal stream from said code checker and stripper means and having a plurality of different operating modes for implementing different algorithms for decoding the different codes, means responsive to the code identification signal from said code checker and stripper means for selecting the operating mode of the digital decoder means required for decoding the encoded compressed signals from said code checker and stripper means, and means for reconstruction filtering of decoded signals from said digital decoder means for producing digital signals fn (out).
-
21. In a data compression method for preparing analog input signals having a substantially Gaussian distribution for storage or transmission, which method includes converting the analog input signal to a digital sample signal stream of equal word length sample signals, digital compression filtering said sample signal stream for generating a stream of compressed signals of equal word length, and digital encoding the compressed signal stream to generate a stream of variable word length encoded compressed signals, the improvement including,
reducing the ratio of σ - /q by a factor of 2-x whenever the average energy level of the analog input signal exceeds a predetermined threshold level for entropy reduction of the sample signal stream, wherein σ
is standard deviation of the compressed signal stream, q is quantization level of the sample signal stream, and x is a non-zero positive integer. - View Dependent Claims (22, 23, 24, 25, 26, 27, 28, 29, 30, 31)
- /q by a factor of 2-x whenever the average energy level of the analog input signal exceeds a predetermined threshold level for entropy reduction of the sample signal stream, wherein σ
-
32. In a data compression method for preparing a digital sample signal stream of equal word length sample signals including digital sample signal streams having a substantially Gaussian distribution for storage or transmission, which method includes digital compression filtering said sample signal stream for generating a stream of compressed signals, and digital encoding the compressed signal stream to generate a stream of variable word length encoded compressed signals, the improvement including,
restricting one or more least significant bits of the sample signals before compression filtering thereof to selected values whenever the average energy level of the signal stream before digital encoding thereof exceeds a predetermined threshold level for entropy reduction thereof.
-
40. In a data compression method for preparing analog input signals including those having a substantially Gaussian distribution for storage or transmission, which method includes converting the analog input signal to a digital sample signal stream, digital compression filtering said sample signal stream for generating a stream of compressed signals, and digital encoding the compressed signal stream using a truncated variable word length code to generate a stream of variable word length encoded compressed signals, the improvement comprising,
changing the amplitude of the analog input signal by a factor of 2x, where x is a non-zero integer whenever the average energy of the analog input signal crosses a predetermined threshold level for changing the entropy thereof, and inserting an identifying code word in the encoded compressed signal stream with each change in the average energy of the analog input signal above and below the threshold level to identify the magnitude of the amplitude reduction.
-
43. In a data reduction system of the type for preparing a digital sample signal stream of equal word length sample signals for storage or transmission,
digital compression filter means for compression filtering the digital sample signal stream and generating a compressed signal stream of equal word length compressed signals, digital encoding means for encoding the compressed signal stream by use of a variable word length code, and means for controlling the quantization level of the digital sample signals and entropy of the sample signal stream supplied to the digital compression filter means by restricting one or more least significant bits of the digital sample signals to selected values in response to a measure of the average energy level of the digital sample signal stream above a predetermined level.
Specification