# US 2006/0149532 A1 · Method and apparatus for enhancing loudness of a speech signal

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- Number: US 2006/0149532 A1
- Document ID: US20060149532A1
- Status: Published application
- Kind: A1
- Application number: 11/026,785
- Filed: 2004-12-31
- Published: 2006-07-06
- Earliest claimed: 2004-12-31
- Assignees: Motorola, Inc.
- Inventors: Marc Boillot; John Harris
- Web page: https://patentgrep.com/patent/US20060149532A1

## CPC

- G10L 19/26: Pre-filtering or post-filtering
- G10L 25/15: the extracted parameters being formant information
- G10L: SPEECH ANALYSIS TECHNIQUES OR SPEECH SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING TECHNIQUES; SPEECH OR AUDIO CODING OR DECODING

## Abstract

A speech filter (108) enhances the loudness of a speech signal by expanding the formant regions of the speech signal beyond a natural bandwidth of the formant regions. The energy level of the speech signal is maintained so that the filtered speech signal contains the same energy as the pre-filtered signal. By expanding the formant regions of the speech signal on a critical band scale corresponding to human hearing, the listener of the speech signal perceives it to be louder even though the signal contains the same energy.

## Claims

### Claim 1

A method of increasing the perceived loudness of a processed speech signal, the processed speech signal corresponding to a natural speech signal and having formant regions and non-formant regions and a natural energy level, the method comprising:
expanding the formant regions of the processed speech signal beyond a natural bandwidth; and
restoring an energy level of the processed speech signal to the natural energy level.

### Claim 2 (depends on 1)

A method of increasing the perceived loudness as defined in claim 1, wherein restoring the energy level occurs upon expanding the formant regions.

### Claim 3 (depends on 1)

A method of increasing the perceived loudness as defined in claim 1, wherein the expanding and restoring are performed on a frame by frame basis of the processed speech signal.

### Claim 4 (depends on 3)

A method of increasing the perceived loudness as defined in claim 3, wherein the expanding and restoring are selectively performed on the processed speech signal when the frame contains substantial vowelic content.

### Claim 5 (depends on 4)

A method of increasing the perceived loudness as defined in claim 4, wherein the vowelic content is determined by a voicing level.

### Claim 6 (depends on 5)

A method of increasing the perceived loudness as defined in claim 5, wherein the voicing level is indicated by a spectral flatness of the speech signal.

### Claim 7 (depends on 3)

A method of increasing the perceived loudness as defined in claim 3, wherein expanding the formant regions is performed to a degree, and wherein the degree depends on a voicing level of a present frame of the processed speech signal.

### Claim 8 (depends on 1)

A method of increasing the perceived loudness as defined in claim 1, wherein expanding and restoring are performed according to a non-linear frequency scale.

### Claim 9 (depends on 8)

A method of increasing the perceived loudness as defined in claim 8, wherein the non-linear scale is a critical band scale.

### Claim 10

A speech filter, comprising,
an analysis portion having a set of filter coefficients determined by warped linear prediction analysis including pole displacement, the analysis portion having unit delay elements;
a synthesis portion having a set of filter coefficients determined by warped linear prediction synthesis including pole displacement, the synthesis portion having unit delay elements; and
a locally recurrent feedback element having a scaling value coupled to the unit delay elements of the analysis and synthesis portions thereby producing non-linear frequency resolution.

### Claim 11 (depends on 10)

A speech filter as defined in claim 10, wherein the scaling value of the locally recurrent feedback element is selected such that the non-linear frequency resolution correspond to a critical band scale.

### Claim 12 (depends on 10)

A speech filter as defined in claim 10, wherein the pole displacement of the synthesis and analysis portions is determined by voicing level analysis.

### Claim 13

A method of processing a speech signal comprising expanding formant regions of the speech signal on a critical band scale using a warped pole displacement filter.