METHOD AND APPARATUS FOR ENHANCING THE MODULATION INDEX OF SPEECH SOUNDS PASSED THROUGH A DIGITAL VOCODER

• US 20150170659A1
• Filed: 12/12/2013
• Published: 06/18/2015
• Est. Priority Date: 12/12/2013
• Status: Active Grant

• Current Assignee: Motorola Solutions, Inc.
• Original Assignee: Motorola Solutions, Inc.
• Inventors: NOVORITA, ROBERT J., KUSHNER, WILLIAM M.
• Granted Patent: US 9,640,185 B2
• Time in Patent Office: Days
• US Class Current: 1/1
• CPC Class Codes: G10L 19/00 Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis in musical instruments G10H
• CPC Class Codes: G10L 19/02 using spectral analysis, e.g. transform vocoders or subband vocoders
• CPC Class Codes: G10L 19/26 Pre-filtering or post-filtering
• CPC Class Codes: G10L 21/02 Speech enhancement, e.g. noise reduction or echo cancellation reducing echo effects in line transmission systems H04B3/20; echo suppression in hands-free telephones H04M9/08
• CPC Class Codes: G10L 21/0224 Processing in the time domain
• CPC Class Codes: G10L 21/0232 Processing in the frequency domain

Abstract

A method and apparatus for enhancing modulation of certain speech sounds, such as trill sounds, are provided for radios which utilize digital vocoders. A digitized speech stream is sampled and the sampling is adjusted to determine, detect and enhance trill nulls in the digitized voice stream by one or more of: frame shifting the digitized speech input stream prior to vocoding, time expanding a digitized speech steam prior to vocoding, time compressing a digitized speech output stream after vocoding, and/or modulation enhancement and filtering of the a digitized speech output stream after vocoding.

Claims

1. A radio, comprising:

a digital vocoder having a predetermined data frame sampling rate; and

at least one processing module for enhancing a modulation index of a predetermined high modulation rate sound event, the at least one processing module detecting energy nulls of the predetermined high modulation rate sound event in a digitized speech stream.

2. The radio of claim 1, wherein the predetermined high modulation rate sound event comprises a trill sound.

3. The radio of claim 1, wherein the at least one processing module comprises:

a pre-vocoder processing module comprising a frame shift module for shifting a data frame of the digitized speech stream forward or backward in time relative to the vocoder frame sampling time to coincide with detected energy nulls.

4. The radio of claim 3, wherein the frame shift module further comprises:

a voice frame energy calculator for calculating voice frame energy at a higher data frame sampling rate than the vocoder;

a differential energy calculator to determine inter-frame differences;

an energy difference classifier;

a state machine to identify and locate the nulls; and

a buffer for shifting the data frame of the digitized speech stream backward or forwards based on the identified and detected energy nulls.

5. The radio of claim 1, wherein the at least one processing module comprises:

a pre-vocoder processing module that receives modulation event null detector information, compares it with frame energy parameter information derived from the vocoder, and modifies the vocoder frame energy parameter to coincide with the detected energy nulls.

6. The radio of claim 1, wherein the at least one processing module comprises:

a pre-vocoder processing module to expand in time a digitized speech input stream to the vocoder, the expansion in time reducing envelope modulation frequencies of the digitized speech input stream below that of the predetermined sampling rate of the vocoder.

7. The radio of claim 6, further comprising:

a post-vocoder processing module to compress in time a digitized speech output stream from the vocoder, thereby reversing the time expansion.

8. The radio of claim 1, wherein the at least one processing module comprises:

a post-vocoder processing module providing a modulation enhancement filter that filters an energy envelope of a digitized speech stream output from the vocoder to enhance the modulation index of the predetermined high modulation rate sound event.

9. The radio of claim 8, wherein the predetermined high modulation rate sound event comprises a trill sound.

10. The radio of claim 9, wherein the modulation enhancement filter comprises:

a time delay element to delay the digitized speech stream output from the vocoder;

an energy envelope calculation element for calculating the modulation energy envelope of the digitized speech stream from the vocoder;

a modulation domain enhancement filter providing a positive gain for predetermined modulation frequencies of the calculated energy envelope; and

an energy envelope gain multiplier for imposing the filtered modulation energy envelope on the delayed digitized speech stream output from the time delay element.

11. A radio system, comprising:

a narrowband vocoder having a predetermined data frame analysis rate;

a plurality of pre-vocoder processor modules comprising;

a high modulation rate (HMR) event detector for detecting modulation amplitude nulls in a received speech signal;

a data frame shifter module;

a module for modifying vocoder frame energy parameters;

a waveform time expansion module;

a plurality of post-vocoder processor modules comprising;

a waveform time compression module;

a modulation domain filter; and

the plurality of pre-vocoder modules and post-vocoder modules optimizing high modulation rate sounds.

12. The radio system of claim 11, wherein the high modulation rate sound comprises an alveolar trill sound.

13. The radio system of claim 11, wherein the data frame shifter module shifts vocoder analysis frames forward and backward in time to coincide with detected modulation amplitude nulls.

14. The radio system of claim 11, wherein the waveform time expansion module expands the speech signal in time to effectively lower signal modulation frequencies.

15. The radio system of claim 14, wherein the waveform time expansion module expands the speech signal in time by 20 (twenty) percent or more.

16. The radio system of claim 14, wherein the waveform compression module time compresses a decoded output signal from the vocoder.

17. A method for processing a digitized speech stream in a radio having a digital vocoder, comprising:

sampling a digitized speech stream used with a vocoder; and

adjusting the sampling to determine and enhance trill nulls in the digitized voice stream.

18. The method of claim 17, wherein adjusting comprises at least one of:

frame shifting a digitized speech input stream prior to vocoding;

time expanding a digitized speech steam prior to vocoding;

time compressing a digitized speech output stream after vocoding; and

modulation enhancement and filtering of a digitized speech output stream after vocoding.

19. The method of claim 17, further comprising:

time shifting a sampled voice frame to maximally capture energy nulls of trill modulation prior to vocoding; and

adjusting a gain parameter of the time shifted voice frame prior to vocoding.

20. The method of claim 19, wherein the gain is adjusted over a faster voice frame rate than that of the digital vocoder, and the gain is adjusted based on a determination of nulls in a digitized speech input stream sampled at the faster voice frame rate.