Method and apparatus for encoding a wideband speech signal utilizing downmixing of a highband component
AssigneeGoogle Technology Holdings LLC
InventorJonathan A. Gibbs
Life of this patent
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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.
Claims17
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.
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.
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.
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.
Dependencies are inferred from the claim text.