Method and device for spectral expansion for an audio signal
View Patent ↗A method and device for automatically increasing the spectral bandwidth of an audio signal including generating a “mapping” (or “prediction”) matrix based on the analysis of a reference wideband signal and a reference narrowband signal, the mapping matrix being a transformation matrix to predict high frequency energy from a low frequency energy envelope, generating an energy envelope analysis of an input narrowband audio signal, generating a resynthesized noise signal by processing a random noise signal with the mapping matrix and the envelope analysis, high-pass filtering the resynthesized noise signal, and summing the high-pass filtered resynthesized noise signal with the original an input narrowband audio signal. Other embodiments are disclosed.
1. A method for automatically expanding the spectral bandwidth of an audio signal comprising:
generating a mapping matrix based on an analysis of a reference wideband signal and a reference narrowband signal, the mapping matrix being a transformation matrix to predict high frequency energy from a lower frequency energy envelope, where the mapping matrix is generated without using a linear predictive coefficient (LPC) method, wherein the mapping matrix is generated based, in part, on using a dB domain for performing a linear prediction;
generating an energy envelope analysis of an input narrowband audio signal;
generating a resynthesized noise signal by processing a random noise signal with the mapping matrix and the energy envelope analysis;
high-pass filtering the resynthesized noise signal;
generating an output audio signal by summing the high-pass filtered resynthesized noise signal with the input narrowband audio signal; and
generating an audible output from a speaker using the output audio signal.
2. The method of claim 1 , wherein the reference wideband and reference narrowband signals are made from a simultaneous recording of a sentence made with an ambient microphone and an ear canal microphone located in an earphone.
3. The method of claim 1 , where the input narrowband audio signal is taken from an ear-canal microphone located in an earphone.
4. The method of claim 1 , where the input narrowband audio signal is taken from a received speech audio signal in a speech telecommunications system.
5. The method of claim 1 , where the summed signal is directed to a speech telecommunications system.
6. The method of claim 1 , where the summed signal is directed to a voice controlled device.
7. The method of claim 1 , where the mapping matrix is generated from a least squares fit analysis of the reference wideband and reference narrowband signals.
8. The method of claim 1 , where the mapping matrix is generated by a linear regression model, where the input reference wideband signals and reference narrowband signals are first converted to a frequency domain representation, and secondly each frequency band envelope is converted to a dB domain representation.
9. A non-transitory computer readable medium containing instructions for spectral enhancement, the execution of the instructions by a processor of a computer system causing the processor to perform operations comprising:
generating a mapping matrix based on an analysis of a reference wideband signal and a reference narrowband signal, the mapping matrix being a transformation matrix to predict high frequency energy from a lower frequency energy envelope, where the mapping matrix is generated without using a linear predictive coefficient (LPC) method, wherein the mapping matrix is generated based, in part, on using a dB domain for performing a linear prediction;
generating an energy envelope analysis of an input narrowband audio signal;
generating a resynthesized noise signal by processing a random noise signal with the mapping matrix and the energy envelope analysis;
high-pass filtering the resynthesized noise signal;
generating an output audio signal by summing the high-pass filtered resynthesized noise signal with the input narrowband audio signal; and
generating an audible output from a speaker and using the output audio signal.