METHOD AND APPARATUS FOR ENCODING A SIGNAL

• US 20120316885A1
• Filed: 06/10/2011
• Published: 12/13/2012
• Est. Priority Date: 06/10/2011
• Status: Active Grant

• Current Assignee: Google Technology Holdings LLC (Alphabet Inc.)
• Original Assignee: Motorola Mobility, Inc. (Lenovo Group Ltd.)
• Inventors: Gibbs, Jonathan A.
• Granted Patent: US 9,070,361 B2
• Time in Patent Office: Days
• US Class Current: 704/500
• 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

8. A method for decoding a signal, the method comprises the steps of:

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 signal by performing a downmixing operation.

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

receiving a wideband 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;

encoding the highband signal with a second encoder;

wherein

the step of filtering the wideband signal to produce the highband signal comprises the step of performing a downmixing operation as part of filtering the wideband signal.

2. The method of claim 1 further comprising the step of preprocessing the wideband signal to produce a preprocessed signal;

and wherein the step of downmixing comprises the step of downmixing the preprocessed signal to produce a down mixed signal.

3. The method of claim 2 wherein the step of preprocessing the wideband signal comprises either a spectral reversal operation or high-pass filtering operation.

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

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

spectrally shaping the decimated signal.

5. The method of claim 2 wherein the step of downmixing the preprocessed signal comprises the step of:

performing a Hilbert Transform on the preprocessed signal to produce two quadrature versions (real and imaginary) of the preprocessed signal.

6. The method of claim 5 wherein the step of downmixing the preprocessed signal further comprises the steps of:

mixing the two quadrature versions (real and imaginary) of the spectrally reversed signal with a cosine and a sine function to produce a mixed signal; and

adding the mixed signals.

7. The method of claim 1 wherein the step of performing a downmixing operation comprises the step of performing a Hilbert Transform.

9. The method of claim 8 wherein the step of filtering the lowband and the highband signals comprises the steps of:

preprocessing the highband signal to produce a preprocessed signal;

downmixing the preprocessed signal to produce a down mixed signal; and

adding the down mixed signal with a lowband signal.

10. The method of claim 9 wherein the step of downmixing the preprocessed signal comprises the step of:

performing a Hilbert Transform on the preprocessed signal to produce two quadrature versions (real and imaginary) of the preprocessed signal.

11. The method of claim 10 wherein the step of downmixing the preprocessed signal further comprises the steps of:

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

adding the mixed signals.

12. The method of claim 8 wherein the downmixing operation comprises a Hilbert Transform operation.

17. The apparatus of claim 16 wherein the downmixing circuitry further comprises:

a pair of mixers mixing the two quadrature versions (real and imaginary) of the spectrally reversed signal with a cosine and a sine function to produce a mixed signal; and

an adder adding the mixed signals.

13. An apparatus comprising:

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

a first encoder encoding the lowband signal;

a second encoder encoding the highband signal; and

wherein the filter bank comprises;

downmixing circuitry downmixing a signal to produce a down mixed signal.

14. The apparatus of claim 13 wherein the filter bank comprises:

preprocessing circuitry either spectrally reversing the wideband signal to produce a spectrally-reversed signal or highpass filtering the wideband signal to produce a highpass filtered signal; and

the downmixing circuitry downmixes the preprocessed signal to produce a down mixed signal.

15. The apparatus of claim 14 wherein the filter bank further comprises:

decimating circuitry decimating the down mixed signal; and

shaping circuitry spectrally shaping the decimated signal.

16. The apparatus of claim 15 wherein the downmixing circuitry comprises Hilbert Transform circuitry performing a Hilbert transform on the preprocessed signal to produce two quadrature versions (real and imaginary) of the preprocessed signal.

17-1. The apparatus of claim 11 wherein the downmixing circuitry comprises Hilbert Transform circuitry.

19. An apparatus comprising:

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

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

a downmixer downmixing a signal to produce a down mixed signal; and

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

20. The apparatus of claim 19 further comprising:

preprocessing circuitry either spectrally reversing the highband signal to produce a spectrally-reversed signal or highpass filtering the highband signal to produce a highpass filtered signal;

wherein the downmixer downmixes the preprocessed signal to produce a down mixed signal; and