Audio decoding based on audio class with control code for post-processing modes
In accordance with an embodiment, a method of generating an encoded audio signal, the method includes estimating a time-frequency energy of an input audio signal from a time-frequency filter bank, computing a global variance of the time-frequency energy, determining a post-processing method according to the global variance, and transmitting an encoded representation of the input audio signal along with an indication of the determined post-processing method.
1. A method of receiving an encoded audio signal, the method comprising:
receiving an encoded audio signal comprising a coded representation of an input audio signal and a control code based on an audio signal class;
decoding the audio signal comprising producing high-band coefficients and low-band coefficients from the audio signal, wherein the high-band coefficients comprises a time-frequency domain representation of high frequency content of the audio signal and the low-band coefficients comprises a time-frequency domain representation of low frequency content of the audio signal;
post-processing the decoded audio signal in a first mode using a hardware-based audio decoder if the control code indicates that the audio signal class is not of a first audio class, wherein post-processing the decoded audio signal in the first mode comprises modifying low-band coefficients and high-band coefficients in the time-frequency domain to correct for audio coding artifacts to produce modified low-band coefficients and modified high-band coefficients;
post-processing the decoded audio signal in a second mode using the hardware-based audio decoder if the control code indicates that the audio signal class is of the first audio class; and
producing an output audio signal based on the post-processed decoded audio signal.
2. The method of claim 1 , wherein:
the post-processing in the first mode is stronger than the post-processing in the second mode;
the coded representation of the input audio signal comprises a low-band bitstream and a high-band bitstream;
decoding the audio signal comprises
decoding the low-band bitstream to produce a low-band signal, and
decoding the high-band bitstream to produce high-band side parameters;
the producing the low-band coefficients comprises performing a time-frequency filter bank analysis of the low-band signal;
the producing the high-band coefficients comprises generating the high-band coefficients based on the high-band side parameters and based on the producing low-band coefficients; and
the producing the audio signal comprises performing a time-frequency filter bank synthesis of the modified low-band coefficients and the modified high-band coefficients.
3. The method of claim 2 , wherein the audio class comprises one of at least three audio classes, and wherein post-processing further comprises adjusting a strength of the modifying according to the audio class.
4. The method of claim 1 , wherein the post-processing in the first mode is stronger than the post-processing in the second mode.
5. The method of claim 4 , wherein:
the post-processing in the first mode comprises compensating for audio bandwidth extension artifacts; and
the post-processing in the second mode comprises not compensating for audio bandwidth extension artifacts.
6. The method of claim 1 , further comprising determining the audio signal class, wherein determining the audio signal class comprises:
monitoring a flag in the control code;
determining that the audio signal class is of the first audio class when the flag is in a first state; and
determining that the audio signal class is not of the first audio class when the flag is in a second state.
7. The method of claim 1 , further comprising determining the audio signal class, wherein determining the audio signal class comprises:
monitoring a post flag in the control code;
when the post flag is in a first state, reading an audio signal class field in the control code to determine the audio signal class; and
when the post flag is in a second state, the audio signal class is the same as an immediately previous audio signal class.
8. The method of claim 7 , wherein the post flag is a one-bit post flag.
9. The method of claim 1 , wherein the first audio class comprises a noise-like audio class.
10. The method of claim 1 , wherein the first audio class comprises a harmonic-like audio class.
11. The method of claim 1 , wherein using the hardware-based audio decoder comprises using a processor.
12. The method of claim 1 , wherein using the hardware-based audio decoder comprises using dedicated hardware.
13. The method of claim 1 , wherein the control code indicates that the audio signal class is of the first audio class when an encoded audio signal has a time/frequency variance that is within a predetermined range.
14. The method of claim 13 , wherein:
the first audio class is a noise-like audio class; and
the predetermined range is less than a predetermined threshold.
15. The method of claim 13 , wherein the time/frequency variance comprises a smoothed time-frequency variance.
16. A system for receiving an encoded audio signal, the system comprising:
a decoder configured to
receive an encoded audio signal comprising a coded representation of an input audio signal and a control code based on an audio signal class, and
decode the audio signal by producing high-band coefficients and low-band coefficients from the audio signal, wherein the high-band coefficients comprises a time-frequency domain representation of high frequency content of the audio signal and the low-band coefficients comprises a time-frequency domain representation of low frequency content of the audio signal; and
a hardware-based post-processor configured to
post-process the decoded audio signal in a first mode if the control code indicates that the audio signal class is not of a first audio class,
post-process the decoded audio signal in a second mode if the control code indicates that the audio signal class is of the first audio class,
produce an output audio signal based on the post-processed decoded audio signal, and
modify low-band coefficients and high-band coefficients in the time-frequency domain to correct for audio coding artifacts to produce modified low-band coefficients and modified high-band coefficients.
17. The system of claim 16 , wherein:
the coded representation of the input audio signal comprises a low-band bitstream and a high-band bitstream; and
the decoder is further configured to:
decode the low-band bitstream to produce a low-band signal,
produce the low-band coefficients by performing a time-frequency filter bank analysis of the low-band signal,
decode the high-band bitstream to produce high-band side parameters, and
generate the high-band coefficients based on the high-band side parameters and based on the producing the low-band coefficients; and
the hardware-based post-processor is further configured to produce the audio signal by performing a time-frequency filter bank synthesis of the modified low-band coefficients and modified high-band coefficients, wherein the post-processing in the first mode is stronger than the post-processing in the second mode.
18. The system of claim 17 , wherein the audio class comprises one of at least three audio classes, and wherein the post-processor is further configured to adjust a strength of the modifying according to the audio class.
19. The system of claim 16 , wherein the post-processing implemented by the hardware-based post-processor in the first mode is stronger than the post-processing in the second mode.
20. The system of claim 19 , wherein:
the post-processing implemented by the hardware-based post-processor in the first mode comprises compensating for audio bandwidth extension artifacts; and
the post-processing implemented by the hardware-based post-processor in the second mode comprises not compensating for audio bandwidth extension artifacts.
21. The system of claim 20 , wherein the hardware-based post-processor is further configured to determine the audio signal class by:
monitoring a flag in the control code;
determining that the audio signal class is of the first audio class when the flag is in a first state; and
determining that the audio signal class is not of the first audio class when the flag is in a second state.
22. The system of claim 16 , wherein the hardware-based post-processor is further configured to determine the audio signal class by performing the following steps:
monitoring a post flag in the control code;
when the post flag is in a first state, reading an audio signal class field in the control code to determine the audio signal class; and
when the post flag is in a second state, setting the audio signal class to be a same audio signal class the same as an immediately previous audio signal class.
23. The system of claim 22 , wherein the post flag is a one-bit post flag.
24. The system of claim 16 , wherein the first audio class comprises a noise-like audio class.
25. The system of claim 16 , wherein the first audio class comprises a harmonic-like audio class.
26. The system of claim 16 , wherein the hardware-based post-processor comprises a processor.
27. The system of claim 16 , wherein the hardware-based post-processor comprises dedicated hardware.
28. The system of claim 16 , wherein the control code indicates that the audio signal class is of the first audio class when an encoded audio signal has a time/frequency variance that is within a predetermined range.
29. A non-transitory computer readable medium with an executable program stored thereon, wherein the program instructs a microprocessor to perform the following steps:
receiving an encoded audio signal comprising a coded representation of an input audio signal and a control code based on an audio signal class;
decoding the audio signal comprising producing high-band coefficients and low-band coefficients from the audio signal, wherein the high-band coefficients comprises a time-frequency domain representation of high frequency content of the audio signal and the low-band coefficients comprises a time-frequency domain representation of low frequency content of the audio signal;
post-processing the decoded audio signal in a first mode if the control code indicates that the audio signal class is not of a first audio class, wherein post-processing the decoded audio signal in the first mode comprises modifying low-band coefficients and high-band coefficients in the time-frequency domain to correct for audio coding artifacts to produce modified low-band coefficients and modified high-band coefficients;
post-processing the decoded audio signal in a second mode if the control code indicates that the audio signal class is of the first audio class; and
producing an output audio signal based on the post-processed decoded audio signal.
30. The non-transitory computer readable medium of claim 29 , wherein
the coded representation of the input audio signal comprises a low-band bitstream and a high-band bitstream;
the steps decoding the audio signal comprises
decoding the low-band bitstream to produce a low-band signal,
producing the low-band coefficients by performing a time-frequency filter bank analysis of the low-band signal,
decoding the high-band bitstream to produce high-band side parameters,
generating the high-band coefficients based on the high-band side parameters and based on the producing the low-band coefficients; and
the step of producing the audio signal comprises performing a time-frequency filter bank synthesis of the modified low-band coefficients and modified high-band coefficients, wherein the post-processing in the first mode is stronger than the post-processing in the second mode.
31. The non-transitory computer readable medium of claim 30 , wherein the audio class comprises one of at least three audio classes, and wherein the post-processing further comprises adjusting a strength of the modifying according to the audio class.
32. The non-transitory computer readable medium of claim 29 , wherein the post-processing in the first mode is stronger than the post-processing in the second mode.
33. The non-transitory computer readable medium of claim 32 , wherein:
the post-processing in the first mode comprises compensating for audio bandwidth extension artifacts; and
the post-processing in the second mode comprises not compensating for audio bandwidth extension artifacts.
34. The non-transitory computer readable medium of claim 33 , wherein the step of determining the audio signal class comprises:
monitoring a flag in the control code;
determining that the audio signal class is of the first audio class when the flag is in a first state; and
determining that the audio signal class is not of the first audio class when the flag is in a second state.
35. The non-transitory computer readable medium of claim 29 , the program further instructs the microprocessor further to perform the step of determining the audio signal class, wherein, the step of determining the audio signal class comprises:
monitoring a post flag in the control code;
determining that the audio signal class is of the first audio class when the post flag is in a first state; and
determining that the audio signal class is not of the first audio class when the post flag is in a second state.
36. The non-transitory computer readable medium of claim 35 , wherein the post flag is a one-bit post flag.
37. The non-transitory computer readable medium of claim 29 , the program further instructs the microprocessor further to perform the step of determining the audio signal class, wherein, the step of determining the audio signal class comprises:
monitoring a post flag in the control code;
when the post flag is in a first state, reading an audio signal class field in the control code to determine the audio signal class; and
when the post flag is in a second state, the audio signal class is the same as an immediately previous audio signal class.
38. The non-transitory computer readable medium of claim 29 , wherein the first audio class comprises a noise-like audio class.
39. The non-transitory computer readable medium of claim 29 , the first audio class comprises a harmonic-like audio class.
40. The non-transitory computer readable medium of claim 29 , wherein the control code indicates that the audio signal class is of the first audio class when an encoded audio signal has a time/frequency variance that is within a predetermined range.