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Method and apparatus for selecting encoding rate in variable rate vocoder

A coding rate and vocoder technology, applied in the field of determining the voice coding rate, can solve the problem that the compression threshold level is not a solution

Inactive Publication Date: 2004-09-22
QUALCOMM INC
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  • Summary
  • Abstract
  • Description
  • Claims
  • Application Information

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Problems solved by technology

If the signal level remains the same, but the correct way to set the threshold level is to increase the signal level with the background noise level, then compressing the threshold level is not the best solution

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  • Method and apparatus for selecting encoding rate in variable rate vocoder
  • Method and apparatus for selecting encoding rate in variable rate vocoder
  • Method and apparatus for selecting encoding rate in variable rate vocoder

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Embodiment Construction

[0013] see figure 1 , to provide the input signal S(n) to the subband energy calculation unit 4 and the subband energy calculation unit 6 . The input signal S(n) contains audio signal and background noise. The audio signal is typically speech, but may also be music. In a typical embodiment, S(n) is provided in the form of 160 samples per twenty millisecond frame. In a typical embodiment, the frequency components of the input signal S(n) range from 0 kHz to 4 kHz, which is approximately similar to the bandwidth of a human speech signal.

[0014] In a typical embodiment, the 4kHz input signal S(n) is filtered into two separate subbands. The discrete subbands are between 0 to 2kHz and 2kHz to 4kHz respectively. In a typical embodiment, subband filters may be used to split the input signal into subbands. This design is well known in the art and was filed on February 1, 1994 under the title "Frequency Selective Adaptive Filtering is described in detail in US Patent Application...

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Abstract

The present invention provides a method by which to reduce the probality of coding low energy unvoiced speech as background noise. An encoding rate is determined by dividing the input signal into subbands using digital subband filters (4) and (6) and comparing the energy in those bands to a set of thresholds in subband rate decision elements (12) and (14) and then examining those comparisons in an encoding rate selector (16). By this method, unvoiced speech can be distinguished from background noise. The present invention, also, provides a means for setting the threshold levels using the signal to noise ratio of the input signal, and the present invention provides a method for coding music through a variable rate vocoder by examining the periodicity of the input signal to distinguish the music from background noise.

Description

technical field [0001] The present invention relates to a vocoder. In particular, the present invention relates to a novel and improved method of determining the speech coding rate in a variable rate vocoder. Background technique [0002] Variable-rate voice compression systems typically use some rate-determining algorithm before starting to encode. This rate determination algorithm assigns a higher bit rate encoding method to segments of the audio signal where speech is present, and a lower bit rate encoding method to silent segments. In this approach, lower average bitrates can be achieved, while the reconstructed speech remains of high quality. Therefore, to operate effectively, a variable-rate speech vocoder requires a robust rate determination algorithm capable of distinguishing speech from silence in various background noise environments. [0003] Such a variable-rate voice compression system or variable-rate voice compression system is disclosed in copending U.S. P...

Claims

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Application Information

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Patent Type & Authority Patents(China)
IPC IPC(8): G10L19/24G10L19/00G10L19/02G10L19/035G10L21/0208G10L25/18G10L25/78H03M7/30
CPCG10L25/78G10L19/22G10L19/10G10L19/0204G10L19/0208G10L19/24G10L19/02G10L21/02
Inventor 安德鲁·P·德雅克威廉·R·加德纳
Owner QUALCOMM INC