Voiced, unvoiced or noise modes in a CELP vocoder
First Claim
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1. A method of processing a signal having a speech component, the signal being organized as a plurality of frames, the method comprising the steps, performed for each frame, of:
- measuring a value for at least one speech characteristic of a frame, wherein the speech characteristic is selected from the group consisting of spectral stationarity, pitch stationarity, high-frequency content, and energy;
comparing the measured value of the selected speech characteristic with at least two thresholds, including a high threshold representing a high value of the selected speech characteristic and a low threshold representing a low value of the selected speech characteristic; and
setting a first flag if the measured value exceeds the high threshold; and
setting a second flag if the measured energy value is below the low threshold;
determining whether the frame lacks a substantial speech component based on the determined flags;
classifying the frame in a noise mode if the frame lacks a substantial speech component, and in a speech mode otherwise; and
generating an encoded frame in accordance with a noise mode coding scheme if the frame is classified in the noise mode, and in accordance with a speech coding scheme if the frame is classified in the speech mode.
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Abstract
A bit rate Codebook Excited Linear Predictor (CELP) communication system which includes a transmitter that organizes a signal containing speech into frames of 40 millisecond duration, and classifies each frame as one of three modes: voiced and stationary, unvoiced or transient, and background noise.
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Citations
24 Claims
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1. A method of processing a signal having a speech component, the signal being organized as a plurality of frames, the method comprising the steps, performed for each frame, of:
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measuring a value for at least one speech characteristic of a frame, wherein the speech characteristic is selected from the group consisting of spectral stationarity, pitch stationarity, high-frequency content, and energy; comparing the measured value of the selected speech characteristic with at least two thresholds, including a high threshold representing a high value of the selected speech characteristic and a low threshold representing a low value of the selected speech characteristic; and setting a first flag if the measured value exceeds the high threshold; and setting a second flag if the measured energy value is below the low threshold; determining whether the frame lacks a substantial speech component based on the determined flags; classifying the frame in a noise mode if the frame lacks a substantial speech component, and in a speech mode otherwise; and generating an encoded frame in accordance with a noise mode coding scheme if the frame is classified in the noise mode, and in accordance with a speech coding scheme if the frame is classified in the speech mode. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 12)
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9. A method of encoding a signal having a speech component, the signal being organized as a plurality of frames, comprising the steps of:
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measuring a value for at least one speech characteristic of a frame, wherein the speech characteristic is selected from the group consisting of spectral stationarity, pitch stationarity, high-frequency content, and energy; comparing the measured value of the selected speech characteristic with at least two thresholds, including a high threshold representing a high value of the selected speech characteristic and a low threshold representing a low value of the selected speech characteristic; setting a first flag if the measured value exceeds the high threshold; and setting a second flag if the measured value is below the low threshold; determining whether the frame lacks a substantial speech component based on the determined flags; classifying the frame in a noise mode, depending on whether the frame lacks a substantial speech component, and in a speech mode otherwise; and generating an encoded frame in accordance with a noise coding scheme when the frame is classified in the noise mode, and in accordance with a speech coding scheme when the frame is classified in the speech mode. - View Dependent Claims (10, 11, 13, 14, 15, 16)
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17. An encoder for encoding a signal having a speech component, the signal being organized as a plurality of frames, comprising:
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means for measuring a value for at least one speech characteristic of a frame from among the plurality of frames, wherein the speech characteristic is selected from the group consisting of spectral stationarity, pitch stationarity, high-frequency content, and energy; a speech characteristic value measurer for comparing the measured value of the selected speech characteristic with at least two thresholds, including a high threshold representing a high value of the selected speech characteristic and a low threshold representing a low value of the selected speech characteristic, setting a first flag if the measured value exceeds the high threshold, and setting a second flag if the measured value falls below the low threshold; means for determining whether the frame lacks a substantial speech component based on an evaluation of the determined flags; a mode classifier for classifying the frame in a noise mode if the frame lacks a substantial speech component, and in a speech mode otherwise; and a frame encoder for generating an encoded frame in accordance with a noise mode coding scheme when the frame is classified in the noise mode, and in accordance with a speech coding scheme when the frame is classified in the speech mode. - View Dependent Claims (18, 19, 20, 21, 22, 23, 24)
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Specification