Voice activity detector based on spectral flatness of input signal
First Claim
1. A voice activity detector that detects talkspurts in an input signal, comprising:
- a frequency spectrum calculator that calculates frequency spectrum of the input signal;
a flatness evaluator that calculates a flatness factor indicating flatness of the frequency spectrum; and
a voice/noise discriminator that determines whether the input signal contains a talkspurt, by comparing the flatness factor of the frequency spectrum with a predetermined threshold.
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Abstract
A voice activity detector that detects talkspurts in a given signal at a high accuracy, so as to improve the quality of voice communication. A frequency spectrum calculator calculates frequency spectrum of a given input signal. A flatness evaluator evaluates the flatness of this power spectrum by, for example, calculating the average of power spectral components and then adding up the differences between those components and the average. The resultant sum of differences, in this case, is used as a flatness factor of the spectrum. A voice/noise discriminator determines whether the input signal contains a talkspurt or not, by comparing the flatness factor of the frequency spectrum with a predetermined threshold.
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Citations
27 Claims
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1. A voice activity detector that detects talkspurts in an input signal, comprising:
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a frequency spectrum calculator that calculates frequency spectrum of the input signal;
a flatness evaluator that calculates a flatness factor indicating flatness of the frequency spectrum; and
a voice/noise discriminator that determines whether the input signal contains a talkspurt, by comparing the flatness factor of the frequency spectrum with a predetermined threshold. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14)
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15. A voice-operated transmitter that turns on and off transmission signal output depending on whether a speech signal is present or not, the transmitter comprising:
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(a) a talkspurt detector comprising;
a frequency spectrum calculator that calculates frequency spectrum of an input signal, a flatness evaluator that calculates a flatness factor indicating flatness of the frequency spectrum, and a voice/noise discriminator that determines whether the input signal contains a talkspurt, by comparing the flatness factor of the frequency spectrum with a predetermined threshold, and sets a talkspurt flag for a talkspurt period or a noise flag for a noise period;
(b) an encoder that produces a coded data stream by encoding the input signal; and
(c) a transmitter that transmits both the coded data stream and talkspurt flag when the talkspurt flag is set, and transmits only the noise flag when the noise flag is set.
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16. A noise canceller that suppresses noise components in an input signal, comprising:
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(a) a noise period detector, comprising;
a plurality of bandpass filters that divides the input signal into a plurality of frequency components, a frequency spectrum calculator that calculates frequency spectrum of the input signal by processing the frequency components supplied from said bandpass filters, a flatness evaluator that calculates a flatness factor indicating flatness of the frequency spectrum, and a voice/noise discriminator that determines whether the input signal contains a talkspurt, by comparing the flatness factor of the frequency spectrum with a predetermined threshold, and sets a talkspurt flag for a talkspurt period or a noise flag for a noise period;
(b) a suppression ratio calculator that estimates noise power of each frequency component when the noise flag is set, and determines a suppression ratio for each frequency component, based on frame power of each frequency component and the estimated noise power; and
(c) a noise suppressor that selectively reduces noise components in the input signal by suppressing the individual frequency components according to the suppression ratios determined by said suppression ratio calculator.
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17. A noise canceller that suppresses noise components in an input signal, comprising:
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(a) a noise period detector, comprising;
a spectrum analyzer that calculates frequency spectrum of the input signal through spectral analysis, a flatness evaluator that calculates a flatness factor indicating flatness of the frequency spectrum, and a voice/noise discriminator that determines whether the input signal contains a talkspurt, by comparing the flatness factor of the frequency spectrum with a predetermined threshold, and sets a talkspurt flag for a talkspurt period or a noise flag for a noise period;
(b) a suppression ratio calculator that estimates a noise power spectrum of noise components in the input signal when the noise flag is set, and determines a suppression ratio for each frequency component, based on the estimated noise power spectrum and the frequency spectrum of the input signal; and
(c) a noise suppressor that selectively reduces noise components in the input signal by suppressing the frequency components according to the suppression ratios determined by said suppression ratio calculator.
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18. A tone detector that detects tone signal components in an input signal, comprising:
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(a) a tone signal detector, comprising;
a frequency spectrum calculator that calculates frequency spectrum of the input signal, a flatness evaluator that calculates a flatness factor indicating flatness of the frequency spectrum, and a tone signal discriminator that determines whether the input signal contains a tone signal, by comparing the flatness factor of the frequency spectrum with a predetermined threshold, and sets a tone detection flag to indicate that a tone signal is present;
(b) a decoder that produces a decoded data stream by decoding the input signal; and
(c) a signal output controller that outputs the decoded data stream as is when the tone detection flag is set, and applies speech processing to the decoded data before outputting when the tone detection flag is not set.
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19. An echo canceller that prevents echoes from occurring, comprising:
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(a) an input talkspurt detector, comprising;
an input sound frequency spectrum calculator that calculates frequency spectrum of an input sound signal, an input sound flatness evaluator that calculates a flatness factor indicating flatness of the input sound frequency spectrum, and an input voice/noise discriminator that determines whether the input sound signal contains a talkspurt, by comparing the flatness factor of the input sound frequency spectrum with a predetermined threshold, and sets an input sound flag to indicate presence of a talkspurt in the input sound signal;
(b) an output talkspurt detector, comprising;
an output sound frequency spectrum calculator that calculates frequency spectrum of an output sound signal, an output sound flatness evaluator that calculates a flatness factor indicating flatness of the output sound frequency spectrum, and an output voice/noise discriminator that determines whether the output sound signal contains a talkspurt, by comparing the flatness factor of the output sound frequency spectrum with a predetermined threshold, and sets an output sound flag to indicate presence of a talkspurt in the output sound signal; and
(c) an echo canceller module that identifies states of the input and output sound signals by monitoring the input and output sound flags, and performing either a subtraction process or an echo training process depending on the identified states, wherein the subtraction process produces a pseudo echo signal by applying echo path characteristics on the output sound signal and subtracts the produced pseudo echo signal from the input sound signal, and wherein the echo canceling process updates the echo path characteristics.
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20. A voice activity detection method for detecting talkspurts in an input signal, comprising the steps of:
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(a) calculating frequency spectrum of the input signal;
(b) calculating a flatness factor indicating flatness of the frequency spectrum; and
(c) determining whether the input signal contains a talkspurt, by comparing the flatness factor of the frequency spectrum with a predetermined threshold. - View Dependent Claims (21, 22, 23, 24, 25, 26, 27)
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Specification