Bandwidth extension of bandlimited audio signals
View Patent ↗A system extends a bandwidth of bandlimited audio signals by analyzing bandlimited audio signals at a transmission cycle rate. The analyzer may obtain a bandlimited parameter at a transmission cycle rate. A mapping device or logic in the system obtains a wideband parameter based on the bandlimited parameter. An audio signal generator generates a highband and/or lowband audio signal based on the wideband parameter at the transmission cycle rate. In some systems, the bandlimited audio signal is analyzed at the transmission cycle rate. The highband and/or lowband audio signals and the combined wideband audio signal are generated at the transmission cycle rate.
1. A system comprising:
an analyzer that analyzes bandlimited audio signals at a transmission cycle rate that obtains a bandlimited parameter at the transmission cycle rate,
a mapping device that obtains a wideband parameter based on the bandlimited parameter, and
an audio signal generator that generates an audio signal based on the wideband parameter at the transmission cycle rate, wherein:
the analyzer generates reliability codes to control the audio signal generator.
2. The system according to claim 1 , where the bandlimited parameter comprises a characteristic parameter that determines a bandlimited spectral envelopes, a pitch, a short-time power ratio, a highband-pass-to-lowband-pass power ratio, or a signal-to-noise ratio.
3. The system according to claim 1 where the wideband parameter comprises a wideband spectral envelope, a characteristic parameter for the determination of wideband spectral envelopes, or a wideband excitation signal.
4. The system according to claim 1 where the mapping device comprises a code book or a neural network that provides a correlation between the bandlimited parameter and the wideband parameter.
5. The system according to claim 1 further comprising:
combination logic that receives the bandlimited audio signal and a highband or lowband audio signal generated by the audio signal generator at the transmission cycle rate.
6. The system according to claim 1 further comprising a controller configured to receive the bandlimited parameter.
7. The system according to claim 6 where the controller controls the mapping device to obtain the wideband parameter at an event rate when a particular condition is met that is lower than the transmission cycle rate.
8. The system according to claim 7 where the particular condition comprises the value of the bandlimited parameter when the bandlimited parameter exceeds a pre-determined limit, or when the difference between the values of the one bandlimited parameter for two subsequent pulses of the event rate when the difference exceeds a pre-determined limit, or when a pre-determined number of cycle rates is exceeded.
9. The system according to claim 7 where the controller controls the audio signal generator to adapt to nominal values for parameters that generate a highband or lowband audio signals, and where the nominal values are modified based on the wideband parameter at the event rate.
10. The system according to claim 6 where the controller comprises a first control unit and a second control unit, and the first control unit generates an event signal, if at least one particular condition is fulfilled, and controls the mapping device to obtain a wideband parameter, only if an at least one event signal is generated, and
the second control unit receives the event signal and the wideband parameter and modifies a nominal value for parameters used to generate a highband or lowband audio signal, only if the at least one event signal is received.
11. The system according to claim 6 where the controller generates reliability codes to control the audio signal generator.
12. The system according to claim 1 where the audio signal generator adapts to nominal values based on a limit maximum increment for every transmission cycle, where the maximum increment is based on a temporal variability of speech generation.
13. The system according to claim 1 where the audio signal generator comprises a sine wave generator.
14. The system according to claim 1 where the audio signal generator comprises a sine wave generator and a noise generator.
15. A method comprising:
analyzing a bandlimited audio signal at a transmission cycle rate and obtaining a bandlimited parameter at the transmission cycle rate,
assigning a wideband parameter to the bandlimited parameter, where assigning the wideband parameter to the bandlimited parameter is based on an event rate that is lower than the transmission cycle rate only when a particular condition is fulfilled,
generating an audio signal based on the wideband parameter at the transmission cycle rate, and
combining the bandlimited audio signal and the generated audio signal to a wideband audio signal at the transmission cycle rate.
16. The method according to claim 15 where the generated audio signal comprises a highband audio signal.
17. The method according to claim 15 where the generated audio signal comprises a lowband audio signal.
18. The method according to claim 15 where:
the bandlimited parameters comprise a characteristic of determination of the bandlimited spectral envelopes, a pitch, a short-time power ratio, a highband-pass-to-lowband-pass power ratio, or a signal-to-noise ratio, and
the wideband parameters comprise wideband spectral envelopes or characteristics for the determination of wideband spectral envelopes or wideband excitation signals.
19. The method according to claim 15 where assigning the wideband parameter to the bandlimited parameter comprises accessing one code book or a neural network.
20. The method according to claim 15 where nominal values for parameters generate at least one of highband or lowband audio signals, and where the nominal values are modified based on the wideband parameter at the event rate.
21. The method according to claim 20 further comprising an audio signal generator that adapts to the nominal values with a limit maximum increment for every transmission cycle, where the maximum increment is based on the temporal variability of speech generation.
22. The method according to claim 20 further comprising:
generating an event signal, if a condition is fulfilled, and
assigning the wideband parameter to the bandlimited parameter and the nominal values for parameters generate at least one of highband or lowband audio signals are only modified, if an event signal is generated.
23. The method according to claim 22 where the condition is fulfilled if a difference between the values of the bandlimited parameter for two subsequent pulses of the event rate exceeds a pre-determined limit.
24. The method according claim 15 further comprising calculating reliability codes for the parameter where the reliability codes are used for controlling the audio signal generator.
25. The method according to claim 24 where the parameter comprises the bandlimited parameter.
26. The method according to claim 15 where the audio signals are generated at the transmission cycle rate by a sine wave generator or by a sine wave generator and a noise generator.
27. A system comprising:
an analyzer that analyzes bandlimited audio signals at a transmission cycle rate that obtains a bandlimited parameter at the transmission cycle rate,
a mapping device that obtains a wideband parameter based on the bandlimited parameter,
an audio signal generator that generates an audio signal based on the wideband parameter at the transmission cycle rate, and
a controller configured to:
receive the bandlimited parameter; and,
control the mapping device to obtain the wideband parameter at an event rate when a particular condition is met that is lower than the transmission cycle rate.
28. The system according to claim 27 , where the bandlimited parameter comprises a characteristic parameter that determines a bandlimited spectral envelopes, a pitch, a short-time power ratio, a highband-pass-to-lowband-pass power ratio, or a signal-to-noise ratio.
29. The system according to claim 27 where the analyzer generates reliability codes to control the audio signal generator.
30. The system according to claim 27 where the wideband parameter comprises a wideband spectral envelope, a characteristic parameter for the determination of wideband spectral envelopes, or a wideband excitation signal.
31. The system according to claim 27 where the mapping device comprises a code book or a neural network that provides a correlation between the bandlimited parameter and the wideband parameter.
32. The system according to claim 27 further comprising:
combination logic that receives the bandlimited audio signal and a highband or lowband audio signal generated by the audio signal generator at the transmission cycle rate.
33. The system according to claim 27 where the particular condition comprises the value of the bandlimited parameter when the bandlimited parameter exceeds a pre-determined limit, or when the difference between the values of the one bandlimited parameter for two subsequent pulses of the event rate when the difference exceeds a pre-determined limit, or when a pre-determined number of cycle rates is exceeded.
34. The system according to claim 27 where the controller controls the audio signal generator to adapt to nominal values for parameters that generate a highband or lowband audio signals, and where the nominal values are modified based on the wideband parameter at the event rate.
35. The system according to claim 27 where the controller comprises a first control unit and a second control unit, and the first control unit generates an event signal, if at least one particular condition is fulfilled, and controls the mapping device to obtain a wideband parameter, only if an at least one event signal is generated, and
the second control unit receives the event signal and the wideband parameter and modifies a nominal value for parameters used to generate a highband or lowband audio signal, only if the at least one event signal is received.
36. The system according to claim 27 where the controller generates reliability codes to control the audio signal generator.
37. The system according to claim 27 where the audio signal generator adapts to nominal values based on a limit maximum increment for every transmission cycle, where the maximum increment is based on a temporal variability of speech generation.
38. The system according to claim 27 where the audio signal generator comprises a sine wave generator.
39. The system according to claim 27 where the audio signal generator comprises a sine wave generator and a noise generator.