High frequency signal construction method and apparatus

Abstract

A method of adding high frequency content to an input signal to form an augmented signal, the method comprising the steps of: (a) providing an initial signal having a first predetermined lower spectral range; (b) utilising the initial signal to form synthesised high frequency components of the initial signal; (c) filtering the initial signal with a low pass filter and filtering the synthesised high frequency components with a high pass filter (d) combining the filtered signals to form the augmented signal.

1 . A method of adding high frequency content to an input signal to form an augmented signal, the method comprising the steps of: 
 (a) providing an initial signal having a first predetermined lower spectral range;    (b) utilising said initial signal to form synthesised high frequency components of said initial signal which extend beyond said lower spectral range;    (c) filtering said initial signal with a low pass filter and filtering said synthesised high frequency components with a high pass filter    (d) combining said high and low pass filtered signals to form said augmented signal.    
     
     
         2 . A method as claimed in  claim 1  wherein said step (b) further comprises: 
 (i) for at least one portion of the input signal, determining the spectral content of said portion;  
 (ii) extrapolating a high frequency end portion of the spectral content to form said synthesised higher frequency components of said signal.  
 
     
     
         3 . A method as claimed in  claim 2  wherein said portion is multiplied with a window function prior to determination of the spectral content and said synthesised higher frequency components are summed in an overlap-add fashion.  
     
     
         4 . A method as claimed in  claim 3  which includes the step of dividing the input signal into a plurality of overlapping blocks, with each block being multiplied by a sliding window function to yield a series of windowed portions from which high frequency components are successively synthesised.  
     
     
         5 . A method as claimed in claims  3  or  4  wherein said window is of a Gaussian or Hanning form.  
     
     
         6 . A method of adding high frequency content to an input signal to form an augmented signal, the method comprising the steps of: 
 (a) providing an initial signal having a first predetermined lower spectral range;    (b) utilising said initial signal to form synthesised high frequency components of said initial signal which extend beyond said lower spectral range, wherein step (b) further comprises: 
 (i) for at least one portion of the input signal, determining the spectral range of said portion;  
 (ii) extrapolating a high frequency end portion of the spectral range to form said synthesised higher frequency components of said signal.  
   
     
     
         7 . A method according to  claim 6  wherein said portion is multiplied with a window function prior to determination of the spectral content, and said synthesised high frequency components are summed in an overlap-add fashion.  
     
     
         8 . A method according to  claim 7  which includes the steps of dividing the input signal into a plurality of overlapping blocks, with each block being multiplied by a sliding window function to yield a series of windowed portions from which high frequency components are successively synthesised.  
     
     
         9 . A method as claimed in any one of  claims 2  to  8  wherein at least some of the highest frequency components of said spectral content are discarded prior to the extrapolation of the remaining high frequency components.  
     
     
         10 . A method as claimed in any one of  claims 6  to  9  in which the step of extrapolating said high frequency end portion comprises the steps of sampling the high frequency components, defining an extrapolation factor based on a geometric progression, and generating said geometric progression on the basis of the sampled high frequency components.  
     
     
         11 . A method as claimed in any previous claim wherein said signal is an audio signal, said lower spectral range corresponds to an audible component of said signal and said high frequency components correspond to ultrasonic components.  
     
     
         12 . A method of adding high frequency content to an input signal substantially as hereinbefore described with reference to FIGS.  5  to  8  of the accompanying drawings.  
     
     
         13 . Apparatus for adding high frequency content to an input signal to form an augmented signal, the apparatus comprising: 
 (a) a synthesising processor for synthesising high frequency components from an initial signal having a first predetermined lower spectral range, said high frequency components extending beyond said lower spectral range;    (b) a low pass filter for filtering said initial signal;    (c) a high pass filter for filtering said synthesised high frequency components;    (d) a combiner for combining said high and low pass filtered signals to form said augmented signal.    
     
     
         14 . An apparatus according to  claim 13  in which said synthesising processor comprises means for determining the spectral content of at least one portion of said input signal and means for extrapolating from a high frequency end portion of said spectral content to form said synthesised high frequency components of said signal.  
     
     
         15 . An apparatus for adding high frequency content to an input signal to form an augmented signal, the apparatus comprising: 
 (a) a synthesising processor for synthesising high frequency components from an initial signal having a first predetermined lower spectral range, said high frequency components extending beyond said lower spectral range;    (b) means for dividing the input signal into a plurality of overlapping portions;    (c) means for determining the spectral content of each of said overlapping portions;    (d) means for extrapolating the high frequency end portion of the spectral content to form said synthesised high frequency components of said signal;    (e) means for summing said synthesised high frequency components in a overlap-add fashion.    
     
     
         16 . Apparatus for adding high frequency content to an input signal substantially as herein before described with reference to FIGS.  5  to  8  of the accompanying drawings.