Method and apparatus for encoding a wideband speech signal utilizing downmixing of a highband component

• US 9,070,361 B2
• Filed: 06/10/2011
• Issued: 06/30/2015
• Est. Priority Date: 06/10/2011
• Status: Active Grant

• Current Assignee: Google Technology Holdings LLC (Alphabet Inc.)
• Original Assignee: Google Technology Holdings LLC (Alphabet Inc.)
• Inventors: Gibbs, Jonathan A.
• Primary Examiner(s): WOZNIAK, JAMES S
• Application Number:
  US13/157,371
• Publication Number:
  US 20120316885A1
• Time in Patent Office: 1,481 Days
• Field of Search: 704500-501, 704/E21.011
• US Class Current: 1/1
• CPC Class Codes: G10L 19/0208 Subband vocoders
• CPC Class Codes: G10L 19/24 Variable rate codecs, e.g. for generating different qualities using a scalable representation such as hierarchical encoding or layered encoding
• CPC Class Codes: G10L 21/038 using band spreading techniques

Abstract

A method and apparatus for encoding a signal is provided herein. During operation a wideband signal that is to be encoded enters a filter bank. A highband signal and a lowband signal are output from the filter bank. Each signal is separately encoded. During the production of the highband signal, a downmixing operation is implemented after preprocessing, and prior to decimating. The downmixing operation greatly reduces system complexity. In fact, it will be observed that the highest sample rate in the prior-art implementation is 64 kHz whereas the sample rate in the system described above remains at 32 kHz or below. This represents a significant complexity saving, as do the reduced number of processing blocks.

Claims

1. A method for encoding a signal, the method comprising:

receiving a wideband speech signal at a filter bank;

filtering the wideband signal to produce a lowband signal and a highband signal;

encoding the lowband signal with a first encoder; and

encoding the highband signal with a second encoder;

wherein

the step of filtering the wideband signal to produce the highband signal comprises;

preprocessing the wideband signal to produce a preprocessed signal; and

performing a downmixing operation on the preprocessed signal, the downmixing operation including

performing a Hilbert Transform on the preprocessed signal to produce two quadrature versions, real and imaginary, of the preprocessed signal;

mixing the two quadrature versions, real and imaginary, of the preprocessed signal with a cosine and a sine function, respectively, to produce mixed signals; and

adding the mixed signals together.

2. The method of claim 1, wherein the downmixing operation is performed on the preprocessed signal to produce a down mixed signal.

3. The method of claim 2 wherein the step of filtering the wideband signal to produce the highband signal further comprises:

decimating the down mixed signal to produce a decimated signal; and

spectrally shaping the decimated signal.

4. The method of claim 1, wherein the step of preprocessing the wideband signal to produce a preprocessed signal includes spectrally-reversing the wideband signal to produce a spectrally-reversed signal.

5. The method of claim 1, wherein the step of preprocessing the wideband speech signal includes a high-pass filtering operation.

6. A method for decoding a signal, the method comprising:

decoding a first signal with a first decoder to produce a lowband signal;

decoding a second signal with a second decoder to produce highband signal; and

filtering the lowband and the highband signals to produce a wideband speech signal by preprocessing the highband signal to produce a preprocessed signal, and performing a downmixing operation on the preprocessed signal, wherein the downmixing operation includes;

performing a Hilbert Transform operation on the preprocessed signal to produce two quadrature versions. real and imaginary, of the preprocessed signal;

mixing the two quadrature versions. real and imaginary, of the preprocessed signal with a cosine and a sine function, respectively, to produce mixed signals; and

adding the mixed signals together.

7. The method of claim 6 wherein the downmixing operation is performed on the preprocessed signal to produce a down mixed signal.

8. The method of claim 7 wherein the step of filtering the lowband and the highband signals includes adding the down mixed signal with a lowband signal.

9. The method of claim 6, wherein the step of preprocessing the highband signal includes a high-pass filtering operation.

10. The method of claim 6, wherein the step of preprocessing the highband signal includes a spectral reversal operation.

11. An apparatus comprising:

a filter bank receiving a wideband speech signal and outputting a lowband signal and a highband signal;

a first encoder encoding the lowband signal; and

a second encoder encoding the highband signal,

wherein the filter bank comprises;

preprocessing circuitry preprocessing the wideband signal to produce- a preprocessed signal; and

downmixing circuitry downmixing the preprocessed signal to produce a down mixed signal,

wherein the downmixing circuitry includes;

Hilbert Transform circuitry performing a Hilbert Transform on the preprocessed signal to produce two quadrature versions, real and imaginary, of the preprocessed signal;

a pair of mixers mixing the two quadrature versions, real and imaginary, of the preprocessed signal with a cosine and a sine function, respectively, to produce mixed signals; and

an adder adding the mixed signals together.

12. The apparatus of claim 11, wherein the preprocessing circuitry spectrally reverses the wideband speech signal to produce a spectrally-reversed signal;

and

the downmixing circuitry downmixes the spectrally-reversed signal to produce a down mixed signal.

13. The apparatus of claim 11, wherein the filter bank further comprises:

decimating circuitry decimating the down mixed signal; and

shaping circuitry spectrally shaping the decimated signal.

14. The apparatus of claim 11, wherein the preprocessing circuitry high-pass filters the wideband speech signal to produce a high-pass filtered signal.

15. An apparatus for decoding speech signals comprising:

a first decoder decoding a first signal to produce a lowband signal;

a second decoder decoding a second signal to produce highband signal;

preprocessing circuitry preprocessing the highband signal to produce a preprocessed signal;

downmixing circuitry that downmixes the preprocessed signal to produce a down mixed signal, wherein the downmixing circuitry includes;

Hilbert Transform circuitry performing a Hilbert Transform on the preprocessed signal to produce two quadrature versions, real and imaginary, of the preprocessed signal;

a pair of mixers mixing the two quadrature versions, real and imaginary, of the preprocessed signal with a cosine and a sine function, respectively, to produce the down mixed signal; and

an adder adding the down mixed signal with the lowband signal.

16. The apparatus of claim 15, wherein

the preprocessing circuitry spectrally reverses the highband signal to produce a spectrally-reversed signal;

and

wherein the downmixing circuitry downmixes the spectrally-reversed signal to produce a down mixed signal.

17. The apparatus of claim 15, wherein the preprocessing circuitry high-pass filters the wideband speech signal to produce a high-pass filtered signal.