Broadband frequency translation for high frequency regeneration

Abstract

An audio signal is conveyed more efficiently by transmitting or recording a baseband of the signal with an estimated spectral envelope and a noise-blending parameter derived from a measure of the signal's noise-like quality. The signal is reconstructed by translating spectral components of the baseband signal to frequencies outside the baseband, adjusting phase of the regenerated components to maintain phase coherency, adjusting spectral shape according to the estimated spectral envelope, and adding noise according to the noise-blending parameter. Preferably, the transmitted or recorded signal also includes an estimated temporal envelope that is used to adjust the temporal shape of the reconstructed signal.

1 . A method for processing an audio signal that comprises: 
 obtaining a frequency-domain representation of a baseband signal having some but not all spectral components of the audio signal;    obtaining an estimated spectral envelope of a residual signal having spectral components of the audio signal that are not in the baseband signal;    deriving a noise-blending parameter from a measure of noise content of the residual signal; and    assembling data representing the frequency-domain representation of the baseband signal, the estimated spectral envelope and the noise-blending parameter into an output signal suitable for transmission or storage.    
     
     
         2 . The method of  claim 1 , wherein the frequency-domain representation of the baseband signal is obtained to represent signal segments that vary in length.  
     
     
         3 . The method of  claim 2  that comprises applying a time-domain aliasing cancellation analysis transform to obtain the frequency-domain representation of the baseband signal.  
     
     
         4 . The method of  claim 1  that comprises: 
 obtaining a frequency-domain representation of the audio signal; and  
 obtaining the frequency-domain representation of the baseband signal from a portion of the frequency-domain representation of the audio signal.  
 
     
     
         5 . The method of  claim 1  that comprises: 
 obtaining a plurality of subband signals representing the audio signal;  
 obtaining the frequency-domain representation of the baseband signal by applying a first analysis filterbank to a first group of one or more subband signals that includes some but not all of the plurality of subband signals; and  
 obtaining the estimated spectral envelope of the residual signal by analyzing a signal obtained by applying a second analysis filterbank to a second group of one or more subband signals that are not included in the first group of subband signals.  
 
     
     
         6 . The method of  claim 5  that comprises: 
 obtaining a temporally flattened representation of the second group of subband signals by modifying the second group of subband signals according to an inverse of an estimated temporal envelope of the second group of subband signals, wherein the estimated spectral envelope of the residual signal and the noise-blending parameter are obtained in response to the temporally flattened representation of the second group of subband signals; and  
 assembling data into the output signal that represents the estimated temporal envelope of the second group of subband signals.  
 
     
     
         7 . The method of  claim 6  that comprises: 
 obtaining a temporally flattened representation of the first group of subband signals by modifying the first group of subband signals according to an inverse of an estimated temporal envelope of the first group of subband signals, wherein the frequency-domain representation of the baseband signal is obtained in response to the temporally flattened representation of the first group of subband signals; and  
 assembling data into the output signal that represents the estimated temporal envelope of the first group of subband signals.  
 
     
     
         8 . A method for processing an audio signal that comprises: 
 obtaining a plurality of subband signals that represent the audio signal;    obtaining a frequency-domain representation of a baseband signal by applying a first analysis filterbank to a first group of one or more subband signals that includes some but not all of the plurality of subband signals;    obtaining a temporally flattened representation of a second group of one or more subband signals that are not included in the first group of subband signals by modifying the second group of subband signals according to an inverse of an estimated temporal envelope of the second group of subband signals;    obtaining an estimated spectral envelope of the temporally flattened representation of the second group of subband signals;    deriving a noise-blending parameter from a measure of noise content of the temporally flattened representation of the second group of subband signals; and    assembling data representing the frequency-domain representation of the baseband signal, the estimated spectral envelope and the noise-blending parameter into an output signal suitable for transmission or storage.    
     
     
         9 . A method for generating a reconstructed audio signal that comprises: 
 receiving a signal containing data representing a baseband signal derived from the audio signal, an estimated spectral envelope, and a noise-blending parameter derived from a measure of noise content of the audio signal;    obtaining from the data a frequency-domain representation of the baseband signal;    obtaining a regenerated signal comprising regenerated spectral components by translating spectral components of the baseband in frequency;    adjusting phase of the regenerated spectral components to maintain phase coherency within the regenerated signal;    obtaining an adjusted regenerated signal by obtaining a noise signal in response to the noise-blending parameter, modifying the regenerated signal by adjusting amplitudes of the regenerated spectral components according to the estimated spectral envelope and the noise-blending parameter, and combining the modified regenerated signal with the noise signal; and    obtaining a time-domain representation of the reconstructed signal corresponding to a combination of the spectral components in the adjusted regenerated signal with spectral components in the frequency-domain representation of the baseband signal.    
     
     
         10 . The method of  claim 9 , wherein the time-domain representation of the reconstructed signal is obtained to represent segments of the reconstructed signal that vary in length.  
     
     
         11 . The method of  claim 10  that comprises applying a time-domain aliasing cancellation synthesis transform to obtain the time-domain representation of the reconstructed signal.  
     
     
         12 . The method of  claim 9  that comprises adapting the translation of spectral components by changing which spectral components that are translated or by changing the frequency amount by which spectral components are translated, wherein the frequency-domain representation of the baseband signal is arranged in blocks and the translation of spectral components is adapted when the regenerated spectral components that result from the adapted translation are deemed to be inaudible.  
     
     
         13 . The method of  claim 9  that obtains the noise signal in such a manner that its spectral components have magnitudes that vary substantially inversely with frequency.  
     
     
         14 . The method of  claim 9  that comprises: 
 obtaining the reconstructed signal by combining the spectral components of the adjusted regenerated signal and the spectral components in the frequency-domain representation of the baseband signal; and  
 obtaining the time-domain representation of the reconstructed signal by applying a synthesis filterbank to the reconstructed signal.  
 
     
     
         15 . The method of  claim 9  that comprises: 
 obtaining a time-domain representation of the baseband signal by applying a first synthesis filterbank to the frequency-domain representation of the baseband signal;  
 obtaining a time-domain representation of the adjusted regenerated signal by applying a second synthesis filterbank to the adjusted regenerated signal; and  
 obtaining the time-domain representation of the reconstructed signal such that it represents a combination of the time-domain representation of the baseband signal and the time-domain representation of the adjusted regenerated signal.  
 
     
     
         16 . The method of  claim 15  that comprises: 
 modifying the time-domain representation of the adjusted regenerated signal according to an estimated temporal envelope obtained from the data; and  
 obtaining the reconstructed signal by combining the time-domain representation of the baseband signal and the modified time-domain representation of the adjusted regenerated signal.  
 
     
     
         17 . The method of  claim 16  that comprises: 
 modifying the time-domain representation of the baseband signal according to another estimated temporal envelope obtained from the data; and  
 obtaining the reconstructed signal by combining the modified time-domain representation of the baseband signal and the modified time-domain representation of the adjusted regenerated signal.  
 
     
     
         18 . A method for generating a reconstructed audio signal that comprises: 
 receiving a signal containing data representing a baseband signal derived from the audio signal, an estimated spectral envelope, an estimated temporal envelope, and a noise-blending parameter;    obtaining from the data a frequency-domain representation of the baseband signal;    obtaining a regenerated signal comprising regenerated spectral components by translating spectral components of the baseband in frequency;    adjusting phase of the regenerated spectral components to maintain phase coherency within the regenerated signal;    obtaining a noise signal in response to the noise-blending parameter;    obtaining an adjusted regenerated signal by adjusting amplitudes of the regenerated spectral components according to the estimated spectral envelope and combining them with the noise signal;    obtaining a time-domain representation of the baseband signal by applying a first synthesis filterbank to the frequency-domain representation of the baseband signal;    obtaining a time-domain representation of the adjusted regenerated signal by applying a second synthesis filterbank to the adjusted regenerated signal and applying modulation according to the estimated temporal envelope; and    obtaining a time-domain representation of the reconstructed signal such that it represents a combination of the time-domain representation of the baseband signal and the modified time-domain representation of the adjusted regenerated signal.    
     
     
         19 . A medium readable by a device and conveying one or more programs of instructions for execution by the device to perform a method for processing an audio signal, wherein the method comprises: 
 obtaining a frequency-domain representation of a baseband signal having some but not all spectral components of the audio signal;    obtaining an estimated spectral envelope of a residual signal having spectral components of the audio signal that are not in the baseband signal;    deriving a noise-blending parameter from a measure of noise content of the residual signal; and    assembling data representing the frequency-domain representation of the baseband signal, the estimated spectral envelope and the noise-blending parameter into an output signal suitable for transmission or storage.    
     
     
         20 . The medium of  claim 19 , wherein the method comprises: 
 obtaining a frequency-domain representation of the audio signal; and    obtaining the frequency-domain representation of the baseband signal from a portion of the frequency-domain representation of the audio signal.    
     
     
         21 . The medium of  claim 19 , wherein the method comprises: 
 obtaining a plurality of subband signals representing the audio signal;    obtaining the frequency-domain representation of the baseband signal by applying a first analysis filterbank to a first group of one or more subband signals that includes some but not all of the plurality of subband signals; and    obtaining the estimated spectral envelope of the residual signal by analyzing a signal obtained by applying a second analysis filterbank to a second group of one or more subband signals that are not included in the first group of subband signals.    
     
     
         22 . The medium of  claim 21 , wherein the method comprises: 
 obtaining a temporally flattened representation of the second group of subband signals by modifying the second group of subband signals according to an inverse of an estimated temporal envelope of the second group of subband signals, wherein the estimated spectral envelope of the residual signal and the noise-blending parameter are obtained in response to the temporally flattened representation of the second group of subband signals; and    assembling data into the output signal that represents the estimated temporal envelope of the second group of subband signals.    
     
     
         23 . The medium of  claim 22 , wherein the method comprises: 
 obtaining a temporally flattened representation of the first group of subband signals by modifying the first group of subband signals according to an inverse of an estimated temporal envelope of the first group of subband signals, wherein the frequency-domain representation of the baseband signal is obtained in response to the temporally flattened representation of the first group of subband signals; and    assembling data into the output signal that represents the estimated temporal envelope of the first group of subband signals.    
     
     
         24 . A medium readable by a device and conveying one or more programs of instructions for execution by the device to perform a method for processing an audio signal, wherein the method comprises: 
 obtaining a plurality of subband signals that represent the audio signal;    obtaining a frequency-domain representation of a baseband signal by applying a first analysis filterbank to a first group of one or more subband signals that includes some but not all of the plurality of subband signals;    obtaining a temporally flattened representation of a second group of one or more subband signals that are not included in the first group of subband signals by modifying the second group of subband signals according to an inverse of an estimated temporal envelope of the second group of subband signals;    obtaining an estimated spectral envelope of the temporally flattened representation of the second group of subband signals;    deriving a noise-blending parameter from a measure of noise content of the temporally flattened representation of the second group of subband signals; and    assembling data representing the frequency-domain representation of the baseband signal, the estimated spectral envelope and the noise-blending parameter into an output signal suitable for transmission or storage.    
     
     
         25 . A medium readable by a device and conveying one or more programs of instructions for execution by the device to perform a method for generating a reconstructed audio signal, wherein the method comprises: 
 receiving a signal containing data representing a baseband signal derived from the audio signal, an estimated spectral envelope, and a noise-blending parameter derived from a measure of noise content of the audio signal;    obtaining from the data a frequency-domain representation of the baseband signal;    obtaining a regenerated signal comprising regenerated spectral components by translating spectral components of the baseband in frequency;    adjusting phase of the regenerated spectral components to maintain phase coherency within the regenerated signal;    obtaining an adjusted regenerated signal by obtaining a noise signal in response to the noise-blending parameter, modifying the regenerated signal by adjusting amplitudes of the regenerated spectral components according to the estimated spectral envelope and the noise-blending parameter, and combining the modified regenerated signal with the noise signal; and    obtaining a time-domain representation of the reconstructed signal corresponding to a combination of the spectral components in the adjusted regenerated signal with spectral components in the frequency-domain representation of the baseband signal.    
     
     
         26 . The medium of  claim 25 , wherein the method obtains the noise signal in such a manner that its spectral components have magnitudes that vary substantially inversely with frequency.  
     
     
         27 . The medium of  claim 25 , wherein the method comprises: 
 obtaining the reconstructed signal by combining the spectral components of the adjusted regenerated signal and the spectral components in the frequency-domain representation of the baseband signal; and    obtaining the time-domain representation of the reconstructed signal by applying a synthesis filterbank to the reconstructed signal.    
     
     
         28 . The medium of  claim 25 , wherein the method comprises: 
 obtaining a time-domain representation of the baseband signal by applying a first synthesis filterbank to the frequency-domain representation of the baseband signal;    obtaining a time-domain representation of the adjusted regenerated signal by applying a second synthesis filterbank to the adjusted regenerated signal; and    obtaining the time-domain representation of the reconstructed signal such that it represents a combination of the time-domain representation of the baseband signal and the time-domain representation of the adjusted regenerated signal.    
     
     
         29 . The medium of  claim 28 , wherein the method comprises: 
 modifying the time-domain representation of the adjusted regenerated signal according to an estimated temporal envelope obtained from the data; and    obtaining the reconstructed signal by combining the time-domain representation of the baseband signal and the modified time-domain representation of the adjusted regenerated signal.    
     
     
         30 . The medium of  claim 29 , wherein the method comprises: 
 modifying the time-domain representation of the baseband signal according to another estimated temporal envelope obtained from the data; and    obtaining the reconstructed signal by combining the modified time-domain representation of the baseband signal and the modified time-domain representation of the adjusted regenerated signal.    
     
     
         31 . A medium readable by a device and conveying one or more programs of instructions for execution by the device to perform a method for generating a reconstructed audio signal, wherein the method comprises: 
 receiving a signal containing data representing a baseband signal derived from the audio signal, an estimated spectral envelope, an estimated temporal envelope, and a noise-blending parameter;    obtaining from the data a frequency-domain representation of the baseband signal;    obtaining a regenerated signal comprising regenerated spectral components by translating spectral components of the baseband in frequency;    adjusting phase of the regenerated spectral components to maintain phase coherency within the regenerated signal;    obtaining a noise signal in response to the noise-blending parameter;    obtaining an adjusted regenerated signal by adjusting amplitudes of the regenerated spectral components according to the estimated spectral envelope and combining them with the noise signal;    obtaining a time-domain representation of the baseband signal by applying a first synthesis filterbank to the frequency-domain representation of the baseband signal;    obtaining a time-domain representation of the adjusted regenerated signal by applying a second synthesis filterbank to the adjusted regenerated signal and applying modulation according to the estimated temporal envelope; and    obtaining a time-domain representation of the reconstructed signal such that it represents a combination of the time-domain representation of the baseband signal and the modified time-domain representation of the adjusted regenerated signal.    
     
     
         32 . A medium conveying an output signal generated by a method for processing an audio signal, wherein the method comprises: 
 obtaining a frequency-domain representation of a baseband signal having some but not all spectral components of the audio signal;    obtaining an estimated spectral envelope of a residual signal having spectral components of the audio signal that are not in the baseband signal;    deriving a noise-blending parameter from a measure of noise content of the residual signal; and    assembling data representing the frequency-domain representation of the baseband signal, the estimated spectral envelope and the noise-blending parameter into the output signal conveyed by the medium.    
     
     
         33 . The medium of  claim 32 , wherein the method comprises: 
 obtaining a temporally flattened representation of at least a portion of the audio signal that is temporally flattened according to an inverse of an estimated temporal envelope, wherein the estimated spectral envelope and the noise-blending parameter are obtained in response to the temporally flattened representation; and    assembling data into the output signal that represents the estimated temporal envelope.