US 7,127,392 B1Granted

Device for and method of detecting voice activity

AssigneeThe United States of America as represented by the National Security Agency

InventorDavid C. Smith

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Abstract

The present invention is a device for and method of detecting voice activity. First, the AM envelope of a segment of a signal of interest is determined. Next, the number of times the AM envelope crosses a user-definable threshold is determined. If there are no crossings, the segment is identified as non-speech. next, the number of points on the AM envelope within a user-definable range is determined. If there are less than a user-definable number of points within the range, the segment is identified as non-speech. Next, the mean, variance, and power ratio of the normalized spectral content of the AM envelope is found and compared to the same for known speech and non-speech. The segment is identified as being of the same type as the known speech or non-speech to which it most closely compares. These steps are repreated for each signal segment of interest.

Claims14

Dependent claims

A voice activity detector, comprising:

a) an absolute value squarer, having an input for receiving a signal, and having an output;
b) a low-pass filter, having an input connected to the output of said absolute value squarer, and having an output;
c) a first function block for finding a mean value, having an input connected to the output of the low pass-filter, and having an output;
d) a second function block for finding a maximum value, having an input connected to the output of the low-pass filter, and having an output;
e) a threshold-crossing detector, including a first user-definable threshold, having an input connected to the output of the low pass filter, and having an output;
f) a third function block for finding a number of points between a user-definable range, having a first input connected to the output of the low-pass filter, having a second input connected to the output of the first function block, having a third input connected to the output of the second function block, and having an output;
g) a comparator, having an input connected to the output of the third function block, and including a second user-definable threshold to which to compare;
h) a subtractor, having a first input connected to the output of the low pass filter, having a second input connected to the output of the second function block, and having an output;
i) a padder, having an input connected to the output of the subtractor, and having an output;
j) a Digital Fast Fourier Transformer, having an input connected to the output of the padder, and having an output;
k) a normalizer, having an input connected to the output of the Digital Fast Fourier Transformer, and having an output;
l) a classifier, having an input connected to the output of the normalizer, and having an output;
and
m) a decision-logic block, having a first input connected to the output of the threshold-crossing detector, having a second input connected to the output of the comparator, having a third input connected to the output of the classifier, and having an output.

11 more elements

A method of detecting voice activity detector, comprising the steps of:

a) receiving a signal;
b) extracting a segment from the signal;
c) computing an absolute value of the signal segment;
d) squaring the result of the last step;
e) finding an Amplitude Modulation (AM) envelope of the result of the last step;
f) computing the mean of the last step;
g) finding a first number of times the AM envelope crosses a first user-definable threshold;
h) if the result of the last step is zero, identifying the signal segment as non-speech and returning to step (b) if there are more signal segments to process, otherwise stopping;
i) finding the maximum value of the AM envelope;
j) finding a second number points on the AM envelope that are within a user-definable range;
k) if the result of the last step is less than a second user-definable threshold then identifying the signal segment as non-speech and returning to step (b) if there are more signal segments to process, otherwise stopping;
l) subtracting the mean value of the AM envelope from the AM envelope;
m) if the result of the last step is not a power of two then padding the result of the last step to form the next highest power of two;
n) finding the spectral content of the AM envelope;
o) finding a normalized vector of the result of the last step;
p) computing a mean, variance, and power ratio of the result of the last step;
and
q) comparing the results of the last step to means, variances, and power ratios of known speech and non-speech, identifying the signal segment as a type to which they most closely compare, and returning to step (b) is there are more signal segments to process.

15 more elements

Dependencies are inferred from the claim text.