Compression and expansion of digitized voice signals
First Claim
Patent Images
1. A method of compressing a digital input signal representative of a continuously-varying input signal into a digital pitch value and a plurality of associated signal values, said digital input signal including a plurality of binary words, each reprsentative of the amplitude of said continuously-varying input signal sampled at successive intervals of time, including the steps of:
- processing a selected plurality of the binary words of said digital input signal to determine the pitch period of said continuously-varying input signal and providing a digital pitch value representative thereof;
performing a time domain harmonic compression on a first plurality of said binary words in response to said pitch value to provide a TDHC output signal representative of the digital input signal but compressed in time by a first predetermined factor, so that said TDHC output signal has a second plurality of binary words equal to said first plurality divided by said first factor;
interpolating, in response to the TDHC output signal, a predetermined number of binary words between each pair of binary words in the TDHC output signal to provide an expanded signal representative of the TDHC output signal but having a plurality of binary words equal to said second plurality multiplied by a second factor;
encoding said expanded signal by means of a delta modulator to provide an encoded output signal wherein each word in the expanded signal is converted into one bit in the encoded output signal representative of the slope of the expanded signal, the encoded output signal providing said signal values.
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Abstract
Speech signal data compression is improved by a first compression using Time Domain Harmonic Scaling (TDHS), wherein two periods of voiced data are averaged together, followed by a second compression using Continuously Variable Slope Delta Modulation (CVSD). Pitch period detection and sampling-rate conversion are also features of the invention.
61 Citations
34 Claims
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1. A method of compressing a digital input signal representative of a continuously-varying input signal into a digital pitch value and a plurality of associated signal values, said digital input signal including a plurality of binary words, each reprsentative of the amplitude of said continuously-varying input signal sampled at successive intervals of time, including the steps of:
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processing a selected plurality of the binary words of said digital input signal to determine the pitch period of said continuously-varying input signal and providing a digital pitch value representative thereof; performing a time domain harmonic compression on a first plurality of said binary words in response to said pitch value to provide a TDHC output signal representative of the digital input signal but compressed in time by a first predetermined factor, so that said TDHC output signal has a second plurality of binary words equal to said first plurality divided by said first factor; interpolating, in response to the TDHC output signal, a predetermined number of binary words between each pair of binary words in the TDHC output signal to provide an expanded signal representative of the TDHC output signal but having a plurality of binary words equal to said second plurality multiplied by a second factor; encoding said expanded signal by means of a delta modulator to provide an encoded output signal wherein each word in the expanded signal is converted into one bit in the encoded output signal representative of the slope of the expanded signal, the encoded output signal providing said signal values. - View Dependent Claims (2, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 34)
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3. The method of claim wherein the step of interpolating includes the step of upsampling the TDHC output signal to provide said predetermined number of binary words between each pair of binary words in the TDHC output signal.
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17. Apparatus for compressing a digital input signal, representative of a continuously-varying input signal, into a digital pitch value and a plurality of associated signal values, said digital input signal including a plurality of binary words, each representative of the amplitude of said continuously-varying input signal sampled at successive intervals of time, comprising:
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means for processing a selected plurality of the binary words of said digital input signal to determine the pitch period of said continuously-varying input signal and for providing a digital pitch value representative thereof; means for performing a time domain harmonic compression on a first plurality of said binary words in response to said pitch value to provide a TDHC output signal representative of the digital input signal but compressed in time by a first predetermined factor, so that said TDHC output signal has a second plurality of binary words equal to said first plurality divided by said first factor; means for interpolating, in response to the TDHC output signal, a predetermined number of binary words between each pair of binary words in the TDHC output signal to provide an expanded signal respresentative of the TDHC output signal but having a plurality of binary words equal to said second plurality multiplied by a second factor; delta modulator means for encoding said expanded signal to provide an encoded output signal wherein each word in the expanded signal is converted into one bit in the encoded output signal representative of the slope of the expanded signal, the encoded output signal providing said signal values. - View Dependent Claims (18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33)
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Specification