Apparatus and method for processing an input audio signal using cascaded filterbanks

Apparatus for processing a time discrete input audio signal, comprising:

• an analysis filterbank comprising a number of analysis filterbank channels, wherein the analysis filterbank is configured for receiving, as an input, the time discrete input audio signal and is configured for filtering the time discrete input audio signal to acquire a plurality of first subband signals;
• and
• a synthesis filterbank that receives, as an input, a group of first subband signals of the plurality of first subband signals, and that synthesizes a time discrete audio intermediate signal using the group of first subband signals, where the group of first subband signals comprises a smaller number of subband signals than the number of analysis filterbank channels of the analysis filterbank,
• wherein the time discrete audio intermediate signal has a bandwidth being smaller than a bandwidth of the time discrete input audio signal, and wherein a sampling rate of the time discrete audio intermediate signal is smaller than a sampling rate of the time discrete input audio signal,
• wherein the analysis filterbank or the synthesis filterbank comprises a prototype window function calculator for calculating a prototype window function by subsampling or interpolating using a stored window function for a filterbank comprising a different size using information on a number of channels for the analysis filterbank or the synthesis filterbank,
• wherein a coefficient of the prototype window function is calculated using a weighted addition of different coefficients of the stored window function, wherein weighting factors of the weighted addition and indices of the different coefficients of the stored window function are derived from integer and fractional parts of a value derived from the different size, an index of the coefficient of the prototype window function, and the information on the number of channels for the analysis filterbank or the synthesis filterbank, and
• wherein at least one of the synthesis filterbank and the analysis filterbank comprises a hardware implementation.

Method of processing a time discrete input audio signal, comprising:

• receiving, by a synthesis filterbank, as an input of the synthesis filterbank, a plurality of time discrete first subband signals representing the time discrete input audio signal and having been generated by an analysis filterbank,
• synthesizing, by the synthesis filterbank, an audio intermediate signal from the plurality of time discrete first subband signals, wherein a number of channels of the synthesis filterbank is smaller than a number of channels of the analysis filterbank;
• and
• receiving, by a further analysis filterbank, as an input of the further analysis filterbank, the audio intermediate signal;
• generating, by the further analysis filterbank, a plurality of time discrete second subband signals from the audio intermediate signal, wherein the further analysis filterbank comprises a number of channels being different from the number of channels of the synthesis filterbank,
• wherein a sampling rate of a time discrete subband signal of the plurality of second time discrete subband signals is different from a sampling rate of a time discrete first subband signal of the plurality of time discrete first subband signals,
• wherein the further analysis filterbank or the synthesis filterbank comprises a prototype window function calculation for calculating a prototype window function by subsampling or interpolating using a stored window function for a filterbank comprising a different size using information on a number of channels for the further analysis filterbank or the synthesis filterbank,
• wherein a coefficient of the prototype window function is calculated using a weighted addition of different coefficients of the stored window function, wherein weighting factors of the weighted addition and indices of the different coefficients of the stored window function are derived from integer and fractional parts of a value derived from the different size, an index of the coefficient of the prototype window function, and the information on the number of channels for the further analysis filterbank or the synthesis filterbank, and
• wherein at least one of the synthesis filterbank and the further analysis filterbank comprises a hardware implementation.

Method for processing a time discrete input audio signal, comprising:

• receiving, as an input of an analysis filterbank, the time discrete input audio signal;
• analysis filtering, by the analysis filterbank, the time discrete input audio signal to acquire a plurality of first subband signals, wherein the analysis filterbank comprises a number of analysis filterbank channels;
• receiving, as an input of a synthesis filterbank, a group of first subband signals of the plurality of first subband signals;
• synthesis filtering, by the synthesis filterbank, the group of first subband signals of the plurality of first subband signals to synthesize a time discrete audio intermediate signal, wherein the group of first subband signals comprises a smaller number of subband signals than the number of analysis filterbank channels of the analysis filterbank,
• wherein the time discrete audio intermediate signal has a bandwidth being smaller than a bandwidth of the input audio signal,
• wherein a sampling rate of the time discrete audio intermediate signal is smaller than a sampling rate of the time discrete input audio signal, wherein the analysis filterbank or the synthesis filterbank comprises a prototype window function calculator for calculating a prototype window function by subsampling or interpolating using a stored window function for a filterbank comprising a different size using information on a number of channels for the analysis filterbank or the synthesis filterbank,
• wherein a coefficient of the prototype window function is calculated using a weighted addition of different coefficients of the stored window function, wherein weighting factors of the weighted addition and indices of the different coefficients of the stored window function are derived from integer and fractional parts of a value derived from the different size, an index of the coefficient of the prototype window function, and the information on the number of channels for the analysis filterbank or the synthesis filterbank, and
• wherein at least one of the synthesis filterbank and the analysis filterbank comprises a hardware implementation.

Non-transitory storage medium having stored thereon a computer program comprising a program code for performing, when running on a computer, a method of processing a time discrete input audio signal, the method comprising:

• receiving, by a synthesis filterbank, as an input of the synthesis filterbank, a plurality of time discrete first subband signals representing the time discrete input audio signal and having been generated by an analysis filterbank,
• synthesizing, by the synthesis filterbank, an audio intermediate signal from the input audio signal, wherein a number of filterbank channels of the synthesis filterbank is smaller than a number of channels of the analysis filterbank;
• receiving, by a further analysis filterbank, as an input of the further analysis filterbank, the audio intermediate signal;
• and
• generating, by the further analysis filterbank, a plurality of time discrete second subband signals from the audio intermediate signal, wherein the further analysis filterbank comprises a number of channels being different from the number of channels of the synthesis filterbank,
• wherein a sampling rate of a time discrete subband signal of the plurality of time discrete second subband signals is different from a sampling rate of a time discrete first subband signal of the plurality of time discrete first subband signals,
• wherein the further analysis filterbank or the synthesis filterbank comprises a prototype window function calculation for calculating a prototype window function by subsampling or interpolating using a stored window function for a filterbank comprising a different size using information on a number of channels for the further analysis filterbank or the synthesis filterbank, and
• wherein a coefficient of the prototype window function is calculated using a weighted addition of different coefficients of the stored window function, wherein weighting factors of the weighted addition and indices of the different coefficients of the stored window function are derived from integer and fractional parts of a value derived from the different size, an index of the coefficient of the prototype window function, and the information on the number of channels for the further analysis filterbank or the synthesis filterbank.

Non-transitory storage medium having stored thereon a computer program comprising a program code for performing, when running on a computer, a method for processing a time discrete input audio signal, the method comprising:

• receiving, as an input of an analysis filterbank, the time discrete input audio signal;
• analysis filtering, by the analysis filterbank, the time discrete input audio signal to acquire a plurality of first subband signals, wherein the analysis filterbank comprises a number of analysis filterbank channels;
• receiving, as an input of a synthesis filterbank, a group of first subband signals of the plurality of first subband signals;
• synthesis filtering, by the synthesis filterbank, the group of first subband signals of the plurality of first subband signals to synthesize a time discrete audio intermediate signal,
• wherein the group of first subband signals comprises a smaller number of subband signals than the number of analysis filterbank channels of the analysis filterbank, wherein the time discrete audio intermediate signal has a bandwidth being smaller than a bandwidth of the input audio signal,
• wherein a sampling rate of the time discrete audio intermediate signal is smaller than a sampling rate of the time discrete input audio signal,
• wherein the analysis filterbank or the synthesis filterbank comprises a prototype window function calculator for calculating a prototype window function by subsampling or interpolating using a stored window function for a filterbank comprising a different size using information on a number of channels for the analysis filterbank or the synthesis filterbank, and
• wherein a coefficient of the prototype window function is calculated using a weighted addition of different coefficients of the stored window function, wherein weighting factors of the weighted addition and indices of the different coefficients of the stored window function are derived from integer and fractional parts of a value derived from the different size, an index of the coefficient of the prototype window function, and the information on the number of channels for the analysis filterbank or the synthesis filterbank.