Audio signal bandwidth extension in CELP-based speech coder
View Patent ↗A method for decoding an audio signal in a decoder having a CELP-based decoder element including a fixed codebook component, at least one pitch period value, and a first decoder output, wherein a bandwidth of the audio signal extends beyond a bandwidth of the CELP-based decoder element. The method includes obtaining an up-sampled fixed codebook signal by up-sampling the fixed codebook component to a higher sample rate, obtaining an up-sampled excitation signal based on the up-sampled fixed codebook signal and an up-sampled pitch period value, and obtaining a composite output signal based on the up-sampled excitation signal and an output signal of the CELP-based decoder element, wherein the composite output signal includes a bandwidth portion that extends beyond a bandwidth of the CELP-based decoder element.
1. A method for decoding a signal in an audio decoder having a CELP-based decoder element that includes a fixed codebook component, at least one pitch period value, and a first decoder output, an audio bandwidth of the signal extends beyond an audio bandwidth of the CELP-based decoder element, the method comprising:
obtaining an up-sampled fixed codebook signal by up-sampling the fixed codebook component to a higher sample rate;
obtaining an up-sampled excitation signal based on the up-sampled fixed codebook signal and an integer up-sampled pitch period value;
obtaining a composite output signal based on the up-sampled excitation signal and an output signal of the CELP-based decoder element; and
deriving the integer up-sampled pitch period value by multiplying the fractional pitch period of the CELP-based decoder element by an up-sampling factor, adding accumulated error from previous integer roundings, and rounding the result,
wherein the composite output signal includes an audio bandwidth portion that extends beyond an audio bandwidth of the CELP-based decoder element.
2. The method of claim 1 further comprising:
obtaining a bandwidth extended signal by applying a non-linear operation to the up-sampled excitation signal,
obtaining the composite output signal by combining the bandwidth extended signal to the CELP-based decoder element with the output signal of the CELP-based decoder element.
3. The method of claim 1 , obtaining the up-sampled excitation signal based on the up-sampled fixed codebook signal and an up-sampled adaptive codebook value, wherein the up-sampled adaptive codebook value is based on the integer up-sampled pitch period value.
4. The method of claim 1 , obtaining the up-sampled excitation signal by filtering the up-sampled fixed codebook signal using an up-sampled long-term predictor filter, wherein the up-sampled long-term predictor filter is characterized by the integer up-sampled pitch period value.
5. The method of claim 1 , obtaining the up-sampled excitation signal by combining the up-sampled fixed codebook signal with the up-sampled adaptive codebook and feeding the result back into the up-sampled adaptive codebook.
6. The method of claim 1 , obtaining the up-sampled excitation signal by passing the up-sampled fixed codebook signal through an up-sampled long-term predictor filter.
7. The method of claim 1 further comprising extending an audio bandwidth of the up-sampled fixed codebook signal beyond the audio bandwidth of the CELP-based decoder element by applying a non-linear operator to the up-sampled fixed codebook.
8. The method of claim 1 extending the audio bandwidth of the up-sampled excitation signal beyond the audio bandwidth of the CELP-based decoder element by applying a non-linear operator to the up-sampled excitation signal.