Apparatus and method for generating audio subband values and apparatus and method for generating time-domain audio samples

Abstract

An embodiment of an apparatus for generating audio subband values in audio subband channels includes an analysis windower for windowing a frame of time-domain audio input samples being in a time sequence extending from an early sample to a later sample using an analysis window function including a sequence of window coefficients to obtain windowed samples. The analysis window function includes a first number of window coefficients derived from a larger window function including a sequence of a larger second number of window coefficients, wherein the window coefficients of the window function are derived by an interpolation of window coefficients of the larger window function. The apparatus further includes a calculator for calculating the audio subband values using the windowed samples.

The invention claimed is: 
     
       1. An apparatus for generating audio subband values in audio subband channels, comprising:
 an analysis windower for windowing a frame of time-domain audio input samples being in a time sequence extending from an early sample to a later sample using an analysis window function comprising a sequence of window coefficients to acquire windowed samples, the analysis window function comprising a first number of window coefficients derived from a larger window function comprising a sequence of a larger second number of window coefficients,   wherein the window coefficients of the window function are derived by an interpolation of window coefficients of the larger window function; and   wherein the second number is an even number; and   a calculator for calculating the audio subband values using the windowed samples.   
     
     
       2. The apparatus according to  claim 1 , wherein the apparatus is adapted to interpolating the window coefficients of the larger window function to acquire the window coefficients of the window function. 
     
     
       3. The apparatus according to  claim 1 , wherein the apparatus or the analysis windower is adapted such that the window coefficients of the window function are linearly interpolated. 
     
     
       4. The apparatus according to  claim 1 , wherein the apparatus or the analysis windower is adapted such that the window coefficients of the analysis window function are interpolated based on two consecutive window coefficients of the larger window function according to the sequence of the window coefficients of the larger window function to acquire one window coefficient of the window function. 
     
     
       5. The apparatus according to  claim 1 , wherein the apparatus or the analysis windower is adapted to acquire the window coefficients c(n) of the analysis window function based on the equation
   c(n)=½(c 2 (2n)+c 2 (2n+1)),
   
       wherein n is an integer indicating an index of the window coefficients c(n), and c 2 (n) is a window coefficient of the larger window function. 
     
     
       6. The apparatus according to  claim 5 , wherein the apparatus or the analysis windower is adapted such that the window coefficients c 2 (n) of the larger window function obey the relations given in the table in Annex 4. 
     
     
       7. The apparatus according to  claim 1 , wherein the analysis windower is adapted such that windowing comprises multiplying the time-domain audio input samples x(n) of the frame to acquire the windowed samples z(n) of the windowed frame based on the equation
   z(n)=x(n)·c(n)
   
       wherein n is an integer indicating an index of the sequence of window coefficients in the range of 0 to T·N−1, wherein c(n) is the window coefficient of the analysis window function corresponding to the index n, wherein x(N·T−1) is the latest time-domain audio input sample of a frame of time-domain audio input samples, wherein the analysis windower is adapted such that the frame of time-domain audio input samples comprises a sequence of T blocks of time-domain audio input samples extending from the earliest to the latest time-domain audio input samples of the frame, each block comprising N time-domain audio input samples, and wherein T and N are positive integers and T is larger than 4. 
     
     
       8. The apparatus according to  claim 1 , wherein the analysis windower is adapted such that the analysis window function comprises a first group of window coefficients comprising a first portion of the sequence of window coefficients and a second group of window coefficients comprising a second portion of the sequence of window coefficients, wherein the first portion comprises less window coefficients than the second portion, wherein an energy value of the window coefficients in the first portion is higher than an energy value of the window coefficients of the second portion, and wherein the first group of window coefficients is used for windowing later time-domain samples and the second group of window coefficients is used for windowing earlier time-domain samples. 
     
     
       9. The apparatus according to  claim 1 , wherein the apparatus is adapted to using an analysis window function being a time-reversed or index-reversed version of a synthesis window function to be used for the audio subband values. 
     
     
       10. The apparatus according to  claim 1 , wherein the analysis windower is adapted such that the larger window function is asymmetric with respect to the sequence of window coefficients. 
     
     
       11. An apparatus for generating time-domain audio samples, comprising:
 a calculator for calculating a sequence of intermediate time-domain samples from audio subband values in audio subband channels, the sequence comprising earlier intermediate time-domain samples and later time-domain samples;   a synthesis windower for windowing the sequence of intermediate time-domain samples using a synthesis window function comprising a sequence of window coefficients to acquire windowed intermediate time-domain samples, the synthesis window function comprising a first number of window coefficients derived from a larger window function comprising a sequence of a larger second number of window coefficients,   wherein the window coefficients of the window function are derived by an interpolation of window coefficients of the larger window function; and   wherein the second number is even; and   an overlap-adder output stage for processing the windowed intermediate time-domain samples to acquire the time-domain samples.   
     
     
       12. The apparatus according to  claim 11 , wherein the apparatus is adapted to interpolating the window coefficients of the larger window function to acquire the window coefficients of the window function. 
     
     
       13. The apparatus according to  claim 11 , wherein the apparatus is adapted such that the window coefficients of the synthesis window function are linearly interpolated. 
     
     
       14. The apparatus according to  claim 11 , wherein the apparatus is adapted such that the window coefficients of the synthesis window function are interpolated based on two consecutive window coefficients of the larger window function according to the sequence of window coefficients of the larger window function to acquire one window coefficient of the window function. 
     
     
       15. The apparatus according to  claim 11 , wherein the apparatus is adapted to acquire the window coefficients c(n) of the synthesis window function based on equation
   c(n)=½(c 2 (2n)c 2 (2n+1)),
   
       wherein c 2 (n) are window coefficients of a larger window function corresponding to the index n. 
     
     
       16. The apparatus according to  claim 15 , wherein the apparatus is adapted such that the window coefficient c 2 (n) fulfill the relations given in the table in Annex 4. 
     
     
       17. The apparatus according to  claim 11 , wherein the synthesis window is adapted such that the windowing comprises multiplying the intermediate time-domain samples g(n) of the sequence of intermediate time-domain samples to acquire the windowed samples z(n) of the windowed frame based on the equation
   z(n)=g(n)·c(T−N−1−n)
   
       for n=0, . . . , T·N−1. 
     
     
       18. The apparatus according to  claim 11 , wherein the synthesis windower is adapted such that the synthesis window function comprises a first group of window coefficients comprising a first portion of the sequence of window coefficients and a second group of window coefficients comprising a second portion of the sequence of window coefficients, the first portion comprising less window coefficients than the second portion, wherein an energy value of the window coefficients in the first portion is higher than an energy value of the window coefficients of the second portion, and wherein the first group of window coefficients is used for windowing later intermediate time-domain samples and the second group of window coefficients is used for windowing earlier intermediate time-domain samples. 
     
     
       19. The apparatus according to  claim 11 , wherein the apparatus is adapted to using the synthesis window function being a time-reverse or index-reversed version of an analysis window function used for generating the audio subband values. 
     
     
       20. The apparatus according to  claim 11 , wherein the synthesis windower is adapted such that the larger window function is asymmetric with respect to a sequence window coefficients. 
     
     
       21. A method for generating audio subband values in audio subband channels, comprising:
 windowing, by an analysis windower, a frame of time-domain audio input samples being in a time sequence extending from an early sample to a later sample using an analysis window function to acquire windowed samples, the analysis window function comprising a first number of window coefficients derived from a larger window function comprising a sequence of a larger second number of window coefficients,   wherein the window coefficients of the window function are derived by an interpolation by window coefficients of the larger window function; and   wherein the second number is an even number; and   calculating, by a calculator, the audio subband values using the windowed samples,   wherein at least one of the analysis windower and the calculator comprises a hardware implementation.   
     
     
       22. A method for generating time-domain audio samples, comprising:
 calculating, by a calculator, a sequence of intermediate time-domain samples from audio subband values in audio subband channels, the sequence comprising earlier intermediate time-domain samples and later intermediate time-domain samples;   windowing, by a synthesis windower, the sequence of intermediate time-domain samples using a synthesis window function to acquire windowed time-domain samples, the synthesis window function comprising a first number of window coefficients derived from a larger window function comprising a sequence of a larger second number of window coefficients,   wherein the window coefficients of the window function are derived by an interpolation of window coefficients of the larger window function; and   wherein the second number is even; and   overlap-adding, by an overlap-adder output stage, the windowed time-domain samples to acquire the time-domain samples;   wherein at least one of the synthesis windower, the calculator and the overlap-adder output stage comprises a hardware implementation.   
     
     
       23. A non-transitory storage medium having stored thereon a program with a program code for executing a method for generating audio subband values in audio subband channels, the method comprising:
 windowing a frame of time-domain audio input samples being in a time sequence extending from an early sample to a later sample using an analysis window function to acquire windowed samples, the analysis window function comprising a first number of window coefficients derived from a larger window function comprising a sequence of a larger second number of window coefficients,   wherein the window coefficients of the window function are derived by an interpolation by window coefficients of the larger window function; and   wherein the second number is an even number; and   calculating the audio subband values using the windowed samples,   when running on a processor.   
     
     
       24. A non-transitory storage medium having stored thereon a program with a program code for executing a method for generating time-domain audio samples, the method comprising:
 calculating a sequence of intermediate time-domain samples from audio subband values in audio subband channels, the sequence comprising earlier intermediate time-domain samples and later intermediate time-domain samples;   windowing the sequence of intermediate time-domain samples using a synthesis window function to acquire windowed time-domain samples, the synthesis window function comprising a first number of window coefficients derived from a larger window function comprising a sequence of a larger second number of window coefficients,   wherein the window coefficients of the window function are derived by an interpolation of window coefficients of the larger window function; and   wherein the second number is even; and   overlap-adding the windowed time-domain samples to acquire the time-domain samples,   
       when running on a processor. 
     
     
       25. An apparatus for generating audio subband values in audio subband channels, comprising:
 an analysis windower for windowing a frame of time-domain audio input samples being in a time sequence extending from an early sample to a later sample using an analysis window function comprising a sequence of window coefficients to acquire windowed samples, the analysis window function comprising a first number of window coefficients derived from a larger window function comprising a sequence of a larger second number of window coefficients,   wherein the window coefficients of the window function are derived by an interpolation of window coefficients of the larger window function; and   wherein the second number is an even number; and   a calculator for calculating the audio subband values using the windowed samples,   wherein the apparatus is adapted to interpolate the window coefficients of the larger window function to acquire the window coefficients of the window function.    
     
     
       26. The apparatus according to  claim 25 , wherein the apparatus or the analysis windower is adapted such that the window coefficients of the analysis window function are interpolated based on two consecutive window coefficients of the larger window function according to the sequence of the window coefficients of the larger window function to acquire one window coefficient of the window function.  
     
     
       27. The apparatus according to  claim 25 , wherein the apparatus or the analysis windower is adapted to acquire the window coefficients c(n) of the analysis window function based on the equation
   c(n)=½(c 2 (2n)+c 2 (2n+1)),
   
       wherein n is an integer indicating an index of the window coefficients c(n), and c 2 (n) is a window coefficient of the larger window function.  
     
     
       28. The apparatus of  claim 27 , wherein the apparatus or the analysis windower is adapted such that the window coefficients c 2 (n) of the larger window function obey the relations given in the table in Annex 4.  
     
     
       29. The apparatus according to  claim 25 , wherein the analysis windower is adapted such that the analysis window function comprises a first group of window coefficients comprising a first portion of the sequence of window coefficients and a second group of window coefficients comprising a second portion of the sequence of window coefficients, wherein the first portion comprises less window coefficients than the second portion, wherein an energy value of the window coefficients in the first portion is higher than an energy value of the window coefficients of the second portion, and wherein the first group of window coefficients is used for windowing later time-domain samples and the second group of window coefficients is used for windowing earlier time-domain samples.  
     
     
       30. The apparatus according to  claim 25 , wherein the apparatus is adapted to using an analysis window function being a time-reversed or index-reversed version of a synthesis window function to be used for the audio subband values.  
     
     
       31. The apparatus according to  claim 25 , wherein the analysis windower is adapted such that the larger window function is asymmetric with respect to the sequence of window coefficients.