Method and system for low bit rate voice encoding and decoding applicable for any reduced bandwidth requirements including wireless

• US 20080140394A1
• Filed: 02/15/2008
• Published: 06/12/2008
• Est. Priority Date: 02/11/2005
• Status: Active Grant

• Current Assignee: Philips North America LLC (Koninklijke Philips N.V.)
• Original Assignee: Holmes Consulting, LLC
• Inventors: Holmes, Clyde
• Granted Patent: US 7,970,607 B2
• Time in Patent Office: Days
• US Class Current: 704/213
• CPC Class Codes: G10L 19/06 Determination or coding of the spectral characteristics, e.g. of the short-term prediction coefficients

Abstract

An implementation of the present invention comprises a voice encoder and decoder method and system that uses voice excitation, eliminating the voice/unvoiced pitch tracking, and the first formant up to 2400 Hertz for synchronous and up to 1600 Hertz for asynchronous, does not use pulse code modulation encoding, but uses the zero crossings only of the first formant, frequency dividing by two and sampling at the formant frequency. The resulting combination uses half or less of the bit rate for excitation and the remainder for short-term spectrum analysis. The spectrum could be updated each 20 milliseconds using 49 bits for the spectrum frame and 49 bits for excitation and one frame bit for synchronous Asynchronous operation could be update at 21.25 milliseconds using 49 bits for the spectrum information and 34 bits for excitation with one bit for frame synchronization. The decoder extracts the excitation, multiplies it by two and uses a Hanning modified sawtooth and spectral flattening to excite the spectrum generator. This waveform produces both even and odd harmonics for both periodic (voiced) and aperiodic (unvoiced) frequencies and gives naturalness to all languages and speakers.

Claims

1. A system for encoding and decoding a voice, comprising:

a vocoder transmitter; and

a vocoder receiver;

wherein the transmitter further comprises;

an automatic gain control (AGC) module;

a first formant filter;

an excitation module operable to implement an excitation analysis;

a spectrum analyzer module adapted to provide a short term frequency spectrum;

an analog to digital converter coupled to the output of the spectrum analyzer module;

a synchronous data channel;

an asynchronous data channel;

a multiplexer operable to combine the outputs from the excitation module and the spectrum analyzer module into a single data stream that is clocked by at least one of;

the synchronous data channel or the asynchronous data channel.

2. The system of claim 1, wherein the automatic gain control is implemented in a digital circuit.

3. The system of claim 1, wherein the automatic gain control is implemented in an analog circuit.

4. The system of claim 1, wherein the automatic gain control is operable to adjust the long-term gain for each level of input.

5. The system of claim 1, wherein the automatic gain control uses only voiced decisions to adjust the long term audio

6. The system of claim 1, wherein the first formant filter is configured as a Bessel filter.

7. The system of claim 6, wherein such filter is implemented using a digital circuit.

8. The system of claim 6, wherein such filter is implemented using an analog circuit.

9. The system of claim 1, wherein the spectrum analyzer module is adapted to provide a short term frequency spectrum in a bandwidth of between approximately 300 to 3000 Hertz.

10. The system of claim 1, wherein the output of the spectrum analyzer module is converted by the analog to digital converter into a 4 bit amplitude for each frequency bands.

11. The system of claim 1, wherein the synchronous data channel is a wireless channel.

12. The system of claim 1, wherein the asynchronous data channel is a wireless channel.

13. The system of claim 1, wherein the synchronous data channel is a digital channel.

14. The system of claim 1 wherein the asynchronous channel is a digital channel.

15. The system of claim 1, wherein the receiver further comprises:

a module for multiply by two excitation extraction and non channel short term spectrum.

16. The system of claim 13, wherein the receiver comprises a demultiplexer operable to separate the excitation from the short term spectrum weighting;

an excitation synthesis module adapted to perform an excitation synthesis;

a spectral flattener module operable to flatten the spectrum to give substantially equal amplitudes to all harmonics;

a spectrum generator operable to process the spectrum weighting excited by the excitation synthesis module and synthesize speech.

17. The system of claim 16, wherein the receiver is a non channel vocoder.

18. The system of claim 1, operable to encode and decode at least one of:

a voice, at 2400 bits per second;

or

a voice, at 4800 bits per second.

19. A system for encoding and decoding speech, comprising:

an encoder including;

a first module adapted to generate and output zero crossings in response to voice excitation in a first formant;

a second module for dividing the output by two and sampling at 2400 Hertz for synchronous such that a resulting combination uses half of a bit rate for excitation and a remainder for short term spectrum analysis; and

means for updating the spectrum each 20 milliseconds using 49 bits for bits for the spectrum and 49 bits for the excitation with one synchronizing bit per frame; and

a decoder including;

a first module for extracting the excitation;

a second module adapted to multiply the excitation by two;

a third module adapted to use a Hanning modified sawtooth and spectral flattening to excite a spectrum generator;

a fourth module for outputting a waveform that produces both even and odd harmonics for both periodic and aperiodic frequencies.

20. A system for encoding and decoding speech, comprising:

an encoder including;

a first module adapted to generate and output zero crossings in response to voice excitation in a first formant;

a second module for dividing the output by two and sampling at 1600 Hertz for asynchronous such that a resulting combination uses the 1600 Hertz for excitation and the remainder for short term spectrum analysis;

means for updating the spectrum each 21.25 milliseconds using 49 bits for the spectrum and 34 bits and one bit for synchronization giving 84 bits per frame; and

a decoder including;

a first module for extracting the excitation;

a second module adapted to multiply the excitation by two;

a third module adapted to use a Hanning modified sawtooth and spectral flattening to excite the spectrum generator; and

a fourth module for outputting a waveform that produces both even and odd harmonics for both periodic and aperiodic frequencies.