Method and apparatus employing a vocoder for speech processing

• US 20030130838A1
• Filed: 05/10/2001
• Published: 07/10/2003
• Est. Priority Date: 02/02/1998
• Status: Active Grant

• Current Assignee: Motorola Solutions, Inc.
• Original Assignee: Motorola, Inc. (Motorola Solutions, Inc.)
• Inventors: Feeney, Gregory A., DʼSouza, Ralph L.
• Granted Patent: US 6,799,159 B2
• Time in Patent Office: Days
• US Class Current: 704/221
• CPC Class Codes: G10L 19/02 using spectral analysis, e.g. transform vocoders or subband vocoders
• CPC Class Codes: G10L 19/10 the excitation function being a multipulse excitation

Abstract

A vocoder (125) is initialized, prior to processing an initial batch of audio data, from parameters extracted from the first frame of audio data (308, 310, 320, 330, 332). In the instant embodiment, parameters affecting voice encoding, which are based on estimates of direct current bias, are used to program a high pass filter (253) incorporated in the vocoder (125).

Claims

1. A method for initializing a vocoder for speech processing, comprising the steps of:

enabling an audio preprocessor when the push-to-talk switch is engaged;

obtaining the first frame of audio data destined for processing by the vocoder;

extracting parameters affecting voice encoding from the batch of audio data;

using compensation data based on the extracted parameters to initialize a previous output value and a previous input value for a filter associated with the vocoder;

thereby initializing the filter to process the batch of audio data; and

processing the batch of audio data through the vocoder, after the step of initializing.

2. The method of claim 1, wherein the extracted parameters comprise an estimate of direct current bias influence on the audio data.

3. The method of claim 2, wherein the step of extracting comprises the steps of:

processing a plurality of samples of audio data to generate an average sample value; and

generating the estimate of direct current bias influence from the average sample value and at least one value derived from the plurality of samples.

4. The method of claim 3, wherein the step of initializing comprises the step of initializing the filter initial conditions using the average sample value and the at least one value from the first frame.

5. The method of claim 3, wherein the step of initializing comprises the steps of:

setting a previous input sample parameter used by the filter to the at least one value; and

setting a previous output sample parameter used by the filter according to a calculation based on the average sample value and the at least one value.

6. A method of processing a batch of speech data through a voice encoder, the voice encoder employing a filter to remove direct current bias from the batch of speech data, the method comprising the steps of :

initializing the filter with parameters representing a previous filter output value and a previous filter input value based on characteristics of samples taken from the first frame of speech data, prior to processing the first frame of speech data through the filter; and

processing the first frame batch of speech data in its entirety through the voice encoder, including the filter, after the initializing step.

7. The method of claim 6, wherein the voice encoder is a multiband excitation type encoder, and the filter is a high pass filter.

8. In a radio communication device, a method comprising the steps of:

enabling an audio input device;

enabling an audio preprocessor selector;

obtaining a batch of audio data from the audio input device for transmission;

preprocessing the batch of audio data to extract parameters for a voice encoder;

applying the parameters to set a previous filter input and output value for the voice encoder, thereby initializing the filter to process the batch of audio data;

processing the batch of audio data through the voice encoder to obtain voice encoded data, after the step of applying;

transmitting the voice encoded data; and

disabling the audio preprocessor selector.

9. The method of claim 8, wherein the parameters comprise compensating values for direct current bias within the batch of audio data.

10. The method of claim 9, wherein the step of applying the parameters comprises the step of initializing a high pass filter with the compensating values for direct current bias.

11. The method of claim 10, further comprising the step of processing audio data, obtained subsequent to the step of applying the parameters, through the voice encoder without further initialization of the high pass filter until the audio input device is subsequently disabled.

12. A radio communication device, comprising:

an audio input device that provides an audio signal representing speech data;

a vocoder coupled to the audio input device and that processes the audio signal to provide an output of an encoded signal representing the speech data, the vocoder having a filter; and

an audio preprocessor coupled to the audio input device, and responsive to the audio signal to set previous output and previous input values for the filter using initialization parameters based on characteristics of the speech data, wherein such initial output and input values is set prior to the processing of the audio signal by the vocoder.

13. The radio communication device of claim 12, wherein the vocoder comprises a filter to compensate for direct current bias, and the initialization parameters comprise compensating values for the filter.

14. The radio communication device of claim 13, wherein the vocoder is a multiband excitation type encoder.