Compression/decompression for preservation of high fidelity speech quality at low bandwidth

• US 5,822,370 A
• Filed: 04/16/1996
• Issued: 10/13/1998
• Est. Priority Date: 04/16/1996
• Status: Expired due to Fees

• Current Assignee: David H. Sitrick
• Original Assignee: Aura Systems Inc.
• Inventors: Graupe, Daniel
• Primary Examiner(s): Chin, Stephen
• Assistant Examiner(s): GHAYOUR, MOHAMMAD H
• Application Number:
  US08/632,914
• Time in Patent Office: 910 Days
• Field of Search: 375/240, 704/205, 704/206, 704/203, 704/204, 704/500, 704/230, 379/93.08
• US Class Current: 375/240
• CPC Class Codes: G10L 19/0204 using subband decomposition
• CPC Class Codes: G10L 25/27 characterised by the analysis technique
• CPC Class Codes: G10L 25/51 for comparison or discrimination

Abstract

The input signal is filtered by bandpass filters having different passbands. These filtered signals are input to power detectors that average the power present in each band. A comparator compares each power level signal to a predetermined power threshold to determine if information is present in any of the bands. If information is present in the upper bands, the information is transformed by a discrete wavelet transform and is thresholded and then shifted to the lower bands. The process by which the shifting operation was accomplished is stored in a code book band. An inverse wavelet transform generates the compressed signal by transforming the signals from the wavelet domain to the time domain. If the signal was compressed, the code book signal is transmitted with the compressed signal to a receiving unit for decompression. If the signal was not compressed, the code book signal and the original input signal is transmitted to the receiving unit. The receiving unit receives the transmitted signal and reconstructs the original input from the transmitted signal, either directly or by re-spreading and transforming the compressed signal from the transmitted signal responsive to the code book signal embedded with the transmitted signal.

Claims

1. A spectra compression system for compressing a spectrum of an input signal having a first predetermined bandwidth into a second predetermined bandwidth, the input signal containing information, the system comprising:

bandpass filter means for generating a plurality of filtered signals for each of a plurality of predetermined bandwidths, responsive to the input signal,

power detector means, responsive to the filtered signals for generating a power signal indicative of a power level of each of the filtered signals;

comparator means for generating a decision signal in response to a comparison of the power signal to a predetermined threshold;

classifier means for generating a classification signal in response to the decision signal;

coding means for generating a code signal in response to the classification signal;

transform means for generating a plurality of transform values responsive to the plurality of filtered signals;

shifting means responsive to the decision signal and the plurality of transform values for moving the information from a first predetermined bandwidth of the plurality of predetermined bandwidths to a second predetermined bandwidth of the plurality of predetermined bandwidths, thus forming a compressed transform signal; and

inverse transform means for generating a compressed signal responsive to the compressed transform signal and to the code signal.

2. The system as in claim 1 further comprising:

wavelet transform (WT) means for providing wavelet transform outputs for each band, said wavelet transform outputs comprising WT parameters having amplitudes responsive to the filtered signals;

wherein the power detector means generates the power signal responsive to detecting the amplitude of the WT parameters.

3. The system as in claim 1 wherein said transform means performs wavelet transforms, and said inverse transform means performs inverse wavelet transforms.

4. The system as in claim 3 wherein said wavelet transforms are discrete, and wherein said inverse wavelet transforms are discrete.

5. The system as in claim 1 wherein said predetermined threshold is different for each of said plurality of predetermined bandwidths.

6. The system as in claim 2 wherein said predetermined threshold is a percentage of the maximum value for the WT parameters for each respective one of the plurality of predetermined bandwidths.

7. The system as in claim 1 further characterized in that said bandpass filter means is comprised of a plurality of bandpass filters, each filter having a predetermined bandwidth, the plurality of bandpass filters thus forming a plurality of predetermined bandwidths and generating the plurality of filtered signals.

8. The system as in claim 7 wherein said power detector means is comprised of a plurality of power detector circuits, each associated with and responsive to a respective separate one of the plurality of bandpass filters for generating the power signal responsive to generating band power signal for each of the detector circuits.

9. The system as in claim 1 further characterized in that said power detector means is comprised of at least one power detector, responsive to the filtered signals, for generating a power signal indicative of a power level of each filtered signal.

10. The system as in claim 1 wherein the comparator means is comprised of at least one comparator circuit for generating the decision signal responsive to comparing transform values with the predetermined threshold value.

11. The system as in claim 1 wherein said shifting means is further comprised of means for additionally moving information from a third predetermined bandwidth of the plurality of predetermined bandwidths to a fourth predetermined bandwidth of the plurality of predetermined bandwidths, thus forming the compressed transform signal.

12. The system as in claim 1 wherein the first predetermined bandwidth is higher in frequency in frequency than the second bandwidth.

13. The system as in claim 11 wherein the third predetermined bandwidth is higher in frequency than the fourth predetermined bandwidth.

14. The system as in claim 1 wherein the coding means is further comprised of a code bandpass filter.

15. The system as in claim 1, further comprising a conditional switch, coupled to the input signal and the classification signal, the conditional switch outputting the input signal if the classification signal indicates a non-compression condition and the conditional switch outputting a null signal if the classification signal indicates a compression condition.

16. The system as in claim 1, further comprising a transmitter, coupled to the coding means, and the shifting means, the transmitter transmitting the code signal and the compressed signal if the classification signal indicates a compression condition and the transmitter transmitting the code signal and the input signal if the classification signal indicates a non-compression condition.

17. The system as in claim 15, further comprising a transmitter, coupled to the conditional switch, the coding means, and the shifting means, the transmitter transmitting the code signal and the compressed signal if the classification signal indicates a compression condition and the transmitter transmitting the code signal and the input signal if the classification signal indicates a non-compression condition.

18. A spectra compression system for compressing a spectrum of an input signal having a first bandwidth into a second bandwidth that is smaller than the first bandwidth, the input signal containing information, the system comprising:

a plurality of bandpass filters for generating a plurality of filtered signals, each bandpass filter having a predetermined bandwidth, the plurality of filtered signal thus being in a plurality of predetermined bandwidths, at least one of the plurality of predetermined bandwidths being in an upper band and the remaining predetermined bandwidths being in a lower band;

a plurality of power detectors, each power detector coupled to a different bandpass filter of the plurality of bandpass filters, each power detector generating a power level signal, indicative of the power level present in the respective filtered signal, in response to squaring an amplitude of the respective filtered signal and averaging the squared amplitude over a predetermined time interval;

a plurality of comparators, each comparator coupled to a different power detector of the plurality of power detectors, each comparator generating a decision signal in response to the power level signal being compared to a predetermined power threshold;

a classifier, coupled to the plurality of comparators, for generating a classification signal in response to the plurality of decision signals, the classification signal indicating a compression condition if at least one of the decision signals indicates that a power level in the upper band is greater than the predetermined power threshold, the classification signal indicating a non-compression condition if none of the decision signals indicate that a power level in the upper band is greater than the predetermined power threshold;

a code bandpass filter, coupled to the classifier, for generating a code signal indicative of the classification signal;

a wavelet transform circuit, coupled to the plurality of filtered signals, for generating a plurality of wavelet transform values;

a shifting circuit, coupled to the wavelet transform, the shifting circuit moving, in response to the classification output signal, the information from the upper band to the lower band, thus generating a plurality of shifted values located in the lower band; and

an inverse wavelet transform circuit, coupled to the shifting circuit, for performing an inverse wavelet transform on the plurality of shifted values, thus producing a compressed signal responsive to the code signal.

19. The system of claim 18 and further comprising a transmitter, coupled to the inverse wavelet transform, for transmitting the code signal and the compressed signal if the compressed condition is indicated and the transmitter transmitting the input signal if the non-compressed condition is indicated.

20. The system as in claim 19 further comprising:

a conditional switch, having an output and being coupled to the input signal and the classifier, the switch allowing the input signal to pass to the output if the classification signal indicates the non-compression condition and the switch allowing a null signal to pass to the output if the classification signal indicates the compressed condition; and

wherein the transmitter is coupled to the conditional switch and responsive to the conditional switch output.

21. The system as in claim 18 wherein the shifting circuit forms a plurality of compressed wavelet transform signals, and the inverse wavelet transform circuit generates an inverse transform signal representative of the compressed signal from the plurality of compressed wavelet transform signals.

22. A decompression system for selectively decompressing an input signal having information which may have been compressed into a lower frequency band of a plurality of frequency bands, the system comprising:

a receiver for receiving a compressed signal comprising information and a decompression code;

a plurality of band pass filters, coupled to the receiver, for generating a plurality of received filtered signals and a decompression code signal responsive to the compressed signal;

a classification circuit, coupled to a first band pass filter of the plurality of band pass filters, for generating a respreading code from the decompression code signal;

a wavelet transform circuit coupled to the plurality of band pass filters, the wavelet transform performing a wavelet transform on the plurality of received filtered signals to provide output of transformed signals;

a respreading circuit, coupled to the classification circuit, for selectively respreading the transformed from the lower frequency band to respective ones of the plurality of frequency bands, to provide an output of respread transformed signals in response to the respreading code; and

an inverse wavelet transform, coupled to the respreading circuit, for generating a decompressed signal from the respread transformed signals.

23. The system as in claim 22, further comprising:

a conditional switch, responsive to the decompression code signal, for selectively outputting one of the decompressed signal and the input signal as a final signal output.

24. A method for compressing the spectrum of an input signal containing information, the method comprising the steps of:

filtering the input signal with a plurality of bandpass filters, each filter having a predetermined bandwidth, to generate a plurality of filtered signals having information;

detecting a power level in the plurality of filtered signals to generate a plurality of power signals, each signal indicative of the power level of a different filtered signal;

comparing the plurality of power signals to a predetermined threshold to generate at least one decision signal in response to a comparison of the power signal to a predetermined threshold;

generating a code signal in response to the result of comparing;

wavelet transforming the plurality of filtered signals to generate a plurality of wavelet transformed signals;

shifting, in response to the result of comparing, information in the plurality of wavelet transformed signals, from a first predetermined bandwidth of the plurality of predetermined bandwidths to a second predetermined bandwidth of the plurality of predetermined bandwidths, thus forming compressed wavelet transform signals; and

inverse wavelet transforming the compressed wavelet transform signals into a compressed transmission signal.

25. The method of claim 24 and further including the step of classifying the result of comparing into a plurality of classes indicative of which predetermined bandwidth the information is located.

26. A system for speech compression and decompression for use with a high bandwidth speech incoming signal for preservation of high fidelity speech quality in a low bandwidth compressed signal, the system comprising:

an array of Band Pass (BP) filters having pass bands of 200-700 Hz (A), 700-1400 Hz (B), 1400-2800 Hz (C), 3500-5600 Hz (D), and 5600-11,200 Hz (E), at a sampling frequency of 22,400 Hz, and an anti-aliasing filter at 11,200 Hz, the array of BP filters receiving the incoming signal and outputting filtered signals;

a subsystem that produces at its output a signal that is proportional to a measure of power in the spectrum at each of the bands A-E, the subsystem squaring the amplitude of the output of each band and averaging this squared output over a time interval of approximately 20 milliseconds;

a decision circuit, coupled to the subsystem, that outputs a "yes" signal if the power in each band A-E is above a threshold value and a "no" signal otherwise, each threshold being pre-setable for each band;

a classifier subsystem for determining compression conditions responsive to the yes/no signals in each band to detect if the filtered signals belong to any of classes (a) to (b) where class (a) to (b) are such that;

(a) corresponds to all situations where no signal lies at bands D and E, and

(b) corresponds to all other situations;

a circuit that shifts, if class (b) has been detected, the spectrum of the output of both bands A and B to band A by compressing the spectrum of bands A and B;

a sub-classification circuit for providing outputs b₁, b₂ or b₃ responsive to classification between and distinguishing sub-classes (b₁ to b₃) of class (b) as follows;

b₁ ;

the power in both of the two highest frequency bands, bands D, E is above their respective thresholds, each of the bands A-E having a predefined threshold,

b2;

the power in band E is above its respective threshold,

b3;

the power in band D is above its threshold;

a band pass filter at 2800-3500 Hz (X), the band X band pass filter being used to output coding signals responsive to the outputs from the subclassification;

a wavelet transform (WT) sub-system that processes the filtered signals generating outputs of WT values,

a shifting subsystem for shifting the WT values from one band to another, and providing a shifted output,

wherein if b₂ has been detected then the WT values of WT band C are shifted to WT band B, and then the moved WT band C values are replaced by those from WT band E which are shifted to Band C;

wherein if sub-class b₃ has been detected then the WT values of WT band B are shifted to WT band A and the WT values of WT band C are shifted to band B, and then the WT values of band D are moved to band C;

wherein if b₁ has been detected then the values of WT band B are moved to band A, then the WT values of band C are moved to band B, then the WT values of D are shifted to WT band B and the WT values of band E are moved to band C; and

an inverse wavelet transform (IWT) stage, for providing a compressed signal output in bands A, B, and C, responsive to the shifted output and the output code signal.

27. The system as in claim 26 wherein the compression of the spectrum of the bands of A and B is by a predetermined ratio.

28. The system as in claim 26, wherein the compressed signal is transmitted.

29. The system as in claim 28 wherein the transmitted compressed signal is coupled to a receiver which reconstructs an approximation of the incoming signal responsive to the code signal and the compressed signal.

30. The system as in claim 29, wherein when moving WT values of any band down from higher to lower bandwidths by 1 band level, each other WT value of the higher band is skipped, and wherein when moving WT values down by 2 levels, each second and third and fourth value of the successive values is skipped, and when moving WT values up in the receiver side, in case of moving WT values up one band, every other value is the arithmetic average of the values on each of its sides, and when moving up 2 bands a linear interpolation between the values both sides is employed.

31. A system for compressing the spectrum of an input signal containing information, the system comprising:

means for filtering the input signal in a plurality of bands each having a pre-determined bandwidth, to generate a plurality of filtered signals having information;

means for detecting a power level in the plurality of filtered signals to generate a plurality of power signals, each of the power signals indicative of the power level of a different respective one of the filtered signals;

means for comparing the plurality of power signals to a pre-determined threshold to generate a decision signal in response to the comparison of at least one of the power signals to the pre-determined threshold;

means for generating a code signal in response to the decision signal;

means for wavelet transforming the plurality of filtered signals to generate a plurality of wavelet transformed signals;

means for shifting information in the plurality of wavelet transformed signals from a first pre-determined bandwidth of the plurality of predetermined bandwidths to a second predetermined bandwidth of the plurality of predetermined bandwidths, thus forming compressed wavelet transform signals responsive to the means for comparing; and

means for inverse wavelet transforming the compressed wavelet transform signals into a compressed signal.

32. The system as in claim 31 further comprising:

means for classifying the result of comparing into a plurality of classes indicative of which predetermined bandwidth the shifted information is located.

33. The system as in claim 31 further comprising means for reconstructing an approximation of the input signal responsive to the compressed signal.

34. A telephony system for communicating telephonic signals from at least a first telephonic device to a second telephonic device, the telephonic signals containing information, the system comprising:

at least one receiver for receiving the telephonic signals; and

a spectra compression system for compressing a spectrum of an input signal having a first predetermined bandwidth into a second predetermined bandwidth, the input signal containing information, the system comprising;

a plurality of bandpass filters, each filter having a predetermined bandwidth, the plurality of bandpass filters thus forming a plurality of predetermined bandwidths and generating a plurality of filtered signals;

at least one power detector, coupled to the plurality of bandpass filters, for generating a power signal indicative of a power level of each filtered signal;

at least one comparator, coupled to the at least one power detector, for generating at least one decision signal in response to a comparison of the power signal to a predetermined threshold;

a classifier, coupled to the at least one comparator, for generating a classification signal in response to the at least one decision signal;

a code bandpass filter, coupled to the classifier, for generating a code signal in response to the classification signal;

a transform circuit, coupled to the plurality of filtered signals, for generating a plurality of transform values;

a shifting circuit, coupled to the plurality of transform values, for moving, in response to the comparison, the information from a first predetermined bandwidth of the plurality of predetermined bandwidths to a second predetermined bandwidth of the plurality of predetermined bandwidths, thus forming at least one compressed transform signal;

an inverse transform circuit, coupled to the shifting circuit, for generating a compressed signal from the at least one compressed transform signal; and

at least one transmitter for transmitting the telephonic signals.