Method and apparatus for speech detection using time-frequency variance

1. A speech presence detection apparatus, comprising:

a plurality of bandpass filters for splitting speech into a bank of sub-bands;

a plurality of shift registers each connected to and associated with one of the bandpass filters for storing the speech of a corresponding sub-band in register elements;

a power determining circuit for determining individual power measurements of the speech stored in each register element;

a variance combining circuit for combining the individual power measurements to provide a time-frequency variance for the individual registers; and

a comparator circuit for comparing the variance with a threshold to indicate whether speech is detected.

2. A method of detecting the presence of speech, comprising the steps of:

(a) calculating a plurality of power samples of speech, each power sample corresponding to a frequency sub-band and time frame of the speech; and

(b) calculating a time-frequency variance of the plurality of power samples; and

(c) comparing the time-frequency variance with at least one threshold to indicate whether speech is detected.

3. A method according to claim 2 , wherein the calculation in step (a) of the plurality of power samples of the speech over time and frequency comprises calculating a power corresponding to different audible bands and different sampling periods.

4. A method according to claim 2 , wherein the calculation in step (a) of the plurality of power samples of the speech over time and frequency comprises the substeps of (a 1 ) bandpass filtering the speech into banks of sub-bands; (a 2 ) storing the speech of a corresponding sub-band; and (a 3 ) calculating a power of the sub-band over a frame.

5. A method according to claim 2 , wherein step (a) of calculating a plurality of power samples of speech comprises

X

ij

=

∑

k

⁢

s

ijk

2

wherein i is the frame index;

wherein j is a frequency sub-band index;

wherein k is the sample index within a frame; and

wherein S ijk is the speech samples for a given frame index i, a given frequency sub-band j and a given sample index k.

6. A method according to claim 2 , wherein step (b) of calculating a time-frequency variance of the plurality of power measurements comprises

VAR

=

∑

X

ij

2

n

-

(

∑

X

ij

n

)

2

wherein i is a frame index;

wherein j is a frequency sub-band index;

wherein X ij is the power measurement for a given time sample index i and a given frequency sub-band j.

7. A method according to claim 6 , wherein the step (a) of calculating each power measurement comprises

X

ij

=

∑

k

⁢

s

ijk

2

wherein i is the frame index;

wherein j is a frequency sub-band index;

wherein k is a sample index within a frame; and

wherein S ijk is the speech samples for a given frame index i, a given frequency sub-band j and a given sample index k.

8. A method according to claim 2 , wherein the calculation in step (c) of comparing the time-frequency variance with at least one threshold indicates that speech is detected when the time-frequency variance is above a threshold.

9. An apparatus for detecting the presence of speech, comprising:

means for calculating a plurality of power samples of speech, each power sample corresponding to a frequency sub-band and time frame of the speech;

means for calculating a time-frequency variance of the plurality of power samples; and

means for comparing the time-frequency variance with at least one threshold to indicate whether speech is detected.

10. An apparatus according to claim 9 , wherein the means for calculating a time-frequency variance of the plurality of power samples comprises

VAR

=

∑

X

ij

2

n

-

(

∑

X

ij

n

)

2

wherein i is a frame index;

wherein j is a frequency sub-band index;

wherein X ij is the power for a given time sample index i and a given frequency sub-band j.