Bandwidth extension method and apparatus for a modified discrete cosine transform audio coder
A method includes defining a transition band for a signal having a spectrum within a first frequency band, where the transition band is defined as a portion of the first frequency band, and is located near an adjacent frequency band that is adjacent to the first frequency band. The method analyzes the transition band to obtain a transition band spectral envelope and a transition band excitation spectrum; estimates an adjacent frequency band spectral envelope; generates an adjacent frequency band excitation spectrum by periodic repetition of at least a part of the transition band excitation spectrum with a repetition period determined by a pitch frequency of the signal; and combines the adjacent frequency band spectral envelope and the adjacent frequency band excitation spectrum to obtain an adjacent frequency band signal spectrum. A signal processing logic for performing the method is also disclosed.
1. A method comprising:
defining a transition band for a signal having a spectrum within a first frequency band, said transition band defined as a portion of said first frequency band, said transition band being located near an adjacent frequency band that is adjacent to said first frequency band;
analyzing said transition band to obtain transition band spectral data;
analyzing said transition band spectral data to obtain a transition band spectral envelope and a transition band excitation spectrum; and
generating an adjacent frequency band signal spectrum using said transition band spectral data comprising:
estimating an adjacent frequency band spectral envelope;
generating an adjacent frequency band excitation spectrum, using said transition band spectral data; and
combining said adjacent band spectral envelope and said adjacent frequency band excitation spectrum to generate said adjacent frequency band signal spectrum.
2. The method of claim 1 , wherein generating an adjacent frequency band excitation spectrum, using said transition band spectral data, further comprises:
generating said adjacent frequency band excitation spectrum by periodic repetition of at least a part of said transition band excitation spectrum with a repetition period determined by a pitch frequency of said signal.
3. The method of claim 2 , wherein generating said adjacent frequency band excitation spectrum, further comprises:
mixing said adjacent frequency band excitation spectrum generated by periodic repetition of at least a part of said transition band excitation spectrum with a pseudo-noise excitation spectrum within said adjacent frequency band.
4. The method of claim 3 , further comprising:
determining a mixing ratio, for mixing said adjacent frequency band excitation spectrum and said pseudo-noise excitation spectrum, using a voicing level estimated from said signal.
5. The method of claim 4 , further comprising:
filling any holes in said adjacent frequency band excitation spectrum due to corresponding holes in said transition band excitation spectrum using said pseudo-noise excitation spectrum.
6. The method of claim 1 , wherein estimating an adjacent frequency band spectral envelope, further comprises:
estimating said signal's energy in said adjacent frequency band.
7. The method of claim 1 , further comprising:
combining said spectrum within said first frequency band and said adjacent frequency band signal spectrum to obtain a bandwidth extended signal spectrum and a corresponding bandwidth extended signal.
8. A method comprising:
defining a transition band for a signal having a spectrum within a first frequency band, said transition band defined as a portion of said first frequency band, said transition band being located near an adjacent frequency band that is adjacent to said first frequency band;
analyzing said transition band to obtain a transition band spectral envelope and a transition band excitation spectrum;
estimating an adjacent frequency band spectral envelope;
generating an adjacent frequency band excitation spectrum by periodic repetition of at least a part of said transition band excitation spectrum with a repetition period determined by a pitch frequency of said signal; and
combining said adjacent frequency band spectral envelope and said adjacent frequency band excitation spectrum to obtain an adjacent frequency band signal spectrum.
9. The method of claim 8 , wherein estimating an adjacent frequency band spectral envelope, further comprises:
estimating said signal's energy in said adjacent frequency band.
10. The method of claim 9 , further comprising:
combining said spectrum within said first frequency band and said adjacent frequency band signal spectrum to obtain a bandwidth extended signal spectrum and a corresponding bandwidth extended signal.
11. The method of claim 10 , wherein generating said adjacent frequency band excitation spectrum, further comprises:
mixing said adjacent frequency band excitation spectrum generated by periodic repetition of at least a part of said transition band excitation spectrum with a pseudo-noise excitation spectrum within said adjacent frequency band.
12. The method of claim 9 , further comprising:
determining a mixing ratio, for mixing said adjacent frequency band excitation spectrum and said pseudo-noise excitation spectrum, using a voicing level estimated from said signal.
13. The method of claim 9 , further comprising:
filling any holes in said adjacent frequency band excitation spectrum due to corresponding holes in said transition band excitation spectrum using said pseudo-noise excitation spectrum.
14. A device comprising:
an input where a signal is provided;
a processor coupled to the input wherein the processor is configured to:
define a transition band for the signal having a spectrum within a first frequency band, said transition band defined as a portion of said first frequency band, said transition band being located near an adjacent frequency band that is adjacent to said first frequency band;
analyze said transition band to obtain a transition band spectral envelope and a transition band excitation spectrum;
estimate an adjacent frequency band spectral envelope;
generate an adjacent frequency band excitation spectrum by periodic repetition of at least a part of said transition band excitation spectrum with a repetition period determined by a pitch frequency of said signal; and
combine said adjacent frequency band spectral envelope and said adjacent frequency band excitation spectrum to obtain an adjacent frequency band signal spectrum.
15. The device of claim 14 , wherein said processor is further configured to:
estimate said signal's energy in said adjacent frequency band.
16. The device of claim 15 , wherein said processor is further configured to:
combine said spectrum within said first frequency band and said adjacent frequency band signal spectrum to obtain a bandwidth extended signal spectrum and a corresponding bandwidth extended signal.
17. The device of claim 15 , wherein said processor is further configured to:
mix said adjacent frequency band excitation spectrum generated by periodic repetition of at least a part of said transition band excitation spectrum with a pseudo-noise excitation spectrum within said adjacent frequency band.
18. The device of claim 17 , wherein processor is further configured to:
determine a mixing ratio, for mixing said adjacent frequency band excitation spectrum and said pseudo-noise excitation spectrum, using a voicing level estimated from said signal.
19. The device of claim 18 , wherein said processor is further configured to:
fill any holes in said adjacent frequency band excitation spectrum due to corresponding holes in said transition band excitation spectrum using said pseudo-noise excitation spectrum.