Method of speech detection

• US 5,572,623 A
• Filed: 10/21/1993
• Issued: 11/05/1996
• Est. Priority Date: 10/21/1992
• Status: Expired due to Term

• Current Assignee: Sextant Avionique
• Original Assignee: Sextant Avionique
• Inventors: Pastor, Dominique
• Primary Examiner(s): MacDonald, Allen R.
• Assistant Examiner(s): ONKA, THOMAS
• Application Number:
  US08/139,740
• Time in Patent Office: 1,111 Days
• Field of Search: 381/34, 381/47, 381/38, 381/43, 381/46, 381/122, 367/1, 342/15, 324/76.47, 324/76.55, 984/260, 395/2.42, 395/2.17, 395/2.34, 395/2.57, 395/2.62
• US Class Current: 704/233
• CPC Class Codes: G10L 2025/932 Decision in previous or following frames
• CPC Class Codes: G10L 2025/937 Signal energy in various frequency bands
• CPC Class Codes: G10L 21/0216 characterised by the method used for estimating noise
• CPC Class Codes: G10L 25/27 characterised by the analysis technique
• CPC Class Codes: G10L 25/87 Detection of discrete points within a voice signal

Abstract

A method for detecting the start and end of speech from a noisy signal including the steps of:

detecting a voiced frame;

searching for noise frames preceding this voiced frame;

constructing an autoregressive model of the noise and a mean noise spectrum;

bleaching the flames preceding the voicing,

searching for the actual start of speech in the bleached frames;

removing the noise from the voiced frames and parameterizing them; and

searching for the actual end of speech.

Claims

1. A method of detecting speech in noisy signals, comprising the steps of:

sampling plural speech frames including plural noise frames, at least one voiced frame and additional plural noise frames after said at least one voiced frame;

identifying said at least one voiced frame;

identifying said plural noise frames preceding said at least one voiced frame;

constructing an autoregressive model of noise and a mean noise spectrum based on said plural noise frames preceding said at least one voiced frame;

bleaching said plural noise frames preceding said at least one voiced frame by using a rejector filter;

removing noise by spectral noise removal from said plural noise frames preceding said at least one voiced frame;

finding an actual start of speech in the bleached plural noise frames;

extracting acoustic vectors used by a voice recognition system from the plural noise-removed frames lying between the actual start of speech and a first of said at least one voiced frame;

removing noise from and parameterizing said at least one voiced frame;

finding an actual end of speech; and

removing noise and parameterizing frames lying between a last of said at least one voiced frame and the actual end of speech.

2. The method as claimed in claim 1, wherein the step of bleaching comprises:

using a rejector filter constructed in said constructing step.

3. The method as claimed in claim 2, further comprising the steps of:

reinitializing processing parameters after the last of said at least one voiced frame has been parameterized.

4. The method as claimed in claim 1, wherein the step of sampling comprises:

sampling frames of signals to be processed; and

processing the detected frames by Fourier transforms, wherein, when two Fourier transforms are consecutive in time, the two Fourier transforms are calculated over three consecutive frames with an overlap of one frame.

5. The method as claimed in claim 1, wherein the step of identifying said at least one voiced frame comprises:

calculating a pitch for each of the sampled plural speech frames; and

determining, for each of the sampled plural speech frames, if a voicing is present in a frame based on the calculated value of a pitch corresponding to said each frame.

6. The method as claimed in claim 5, wherein the step of identifying said at least one voiced frame comprises:

identifying said at least one voiced frame after having determined that at least three voiced frames are in series without a hole bigger than a maximum hole size.

7. The method as claimed in claim 5, wherein the step of calculating the pitch of one of said sampled plural speech frames comprises:

calculating a correlation of a signal of said one frame with a delayed form of the signal of said one frame.

8. The method as claimed in claim 1, further comprising the step of:

detecting unvoiced sounds by thresholding.

9. The method as claimed in claim 1, further comprising the step of:

detecting unvoiced speech based on a distance between a vocal kernel and a fricative block, and a size of said fricative block.

10. The method as claimed in claim 1, wherein the steps of removing noise from said plural noise frames preceding said at least one voiced frame comprises:

obtaining a mean noise spectrum of the plural noise frames preceding said at least one voiced frame by Wiener filtering; and

removing noise based on the obtained mean noise spectrum.

11. The method as claimed in claim 10, further comprising the step of:

applying a smooth correlogram to the mean noise spectrum.