Method and apparatus for selective signal coding based on core encoder performance
In a selective signal encoder, an input signal is first encoded using a core layer encoder to produce a core layer encoded signal. The core layer encoded signal is decoded to produce a reconstructed signal and an error signal is generated as the difference between the reconstructed signal and the input signal. The reconstructed signal is compared to the input signal. One of two or more enhancement layer encoders selected dependent upon the comparison and used to encode the error signal. The core layer encoded signal, the enhancement layer encoded signal and the selection indicator are output to the channel (for transmission or storage, for example).
1. A method for coding an input audio signal, the method comprising:
encoding the input signal using a core layer encoder to produce a core layer encoded signal;
decoding the core layer encoded signal to produce a reconstructed signal;
comparing the reconstructed signal to the input signal, wherein the comparing comprises estimating an energy E_err of the reconstructed signal that contain errors, determining a ratio S(k)/Sc(k) of component S(k) of the input signal to the component Sc(k) of the reconstructed signal exceeds a threshold value and summing the energies of those components Sc(k) of the reconstructed signal when the ratio S(k)/Sc(k) does not exceed the threshold value;
selecting an enhancement layer encoder from a plurality of enhancement layer encoders dependent upon the comparison between the reconstructed signal and the input signal; and
generating an enhancement layer encoded signal using the selected enhancement layer encoder, the enhancement layer encoded signal being dependent upon the input signal.
2. A method in accordance with claim 1 , further comprising:
generating an error signal as the difference between the reconstructed signal and the input signal,
wherein generating the enhancement layer encoded signal comprises encoding the error signal.
3. A method in accordance with claim 2 , wherein the error signal comprises a weighted difference between the reconstructed signal and the input signal.
4. A method in accordance with claim 1 , wherein comparing the reconstructed signal to the input signal further comprises:
estimating an energy E_tot as a summation of energies in all components of the reconstructed signal;
and
comparing the energy E_tot to the energy E_err.
5. A method in accordance with claim 4 , further comprising:
transforming the reconstructed signal to produce the components of the reconstructed signal,
wherein the transform is selected from the group of transforms consisting of a Fourier transform, a modified discrete cosine transform (MDCT) and a wavelet transform.
6. A method in accordance with claim 4 , further comprising:
transforming the reconstructed signal to produce the components of the reconstructed signal; and
transforming the input signal to produce the components of the input signal,
wherein the transform is selected from the group of transforms consisting of a Fourier transform, a modified discrete cosine transform (MDCT) and a wavelet transform.
7. A method in accordance with claim 1 , wherein the energy of a component Sc(k) is estimated as |Sc(k)| P , and wherein the energy of a component S(k) is estimated as |Sc(k)| P where P is a number greater than zero.
8. A method in accordance with claim 4 , wherein comparing the energy E_tot to the energy E_err comprises:
comparing the ratio of energies E_err/E_tot to a threshold value.
9. A method in accordance with claim 1 , wherein the core layer encoded comprises a speech encoder.
10. A method in accordance with claim 1 , further comprising outputting the core layer encoded signal, the enhancement layer encoded signal and an indicator of the selected enhancement layer encoder to a channel.
11. A selective signal encoder comprising a processor that includes instructions for executing functions of the encoder, the encoder comprising:
a core layer encoder that receives an input audio signal to be encoded and produces a core layer encoded signal;
a core layer decoder that receives the core layer encoded signal as input and produces a reconstructed signal;
a plurality of enhancement layer encoders each selectable to encode an error signal to produce an enhanced layer encoded signal, the error signal comprising a difference between the input signal and the reconstructed signal; and
a comparator/selector module that selects an enhancement layer encoder of the plurality of enhancement layer encoders dependent upon a comparison of the input signal and core layer encoded signal,
wherein the comparator/selector module estimates an energy E_err of the reconstructed signal that contains errors, determines a ratio S(k)/Sc(k) of component S(k) of the input signal to the component Sc(k) of the reconstructed signal exceeds a threshold value and sum the energies in components Sc(k) of the reconstructed signal when the ratio S(k)/Sc(k) does not exceed the threshold value, and further,
wherein the input signal is encoded as the core layer encoded signal, the enhanced layer encoded signal and an indicator of the selected enhanced layer encoder.
12. A selective signal encoder in accordance with claim 11 , wherein the core layer encoder comprises a speech encoder.
13. A selective signal encoder in accordance with claim 11 , wherein the comparator/selector module further:
estimates an energy E_tot as a summation of energies in all components of the reconstructed signal;
and
compares the energy E_tot to the energy E_err.
14. A selective signal encoder in accordance with claim 13 , wherein the comparator/selector module compares the energy E_tot to the energy E_err by comparing the ratio of energies E_err/E_tot to a threshold value.
15. A selective signal encoder in accordance with claim 13 , wherein the components of the reconstructed signal and the components of the input signal are computed via a transform selected from the group of transforms consisting of a Fourier transform, a modified discrete cosine transform (MDCT) and a wavelet transform.