System aspects of an audio codec

A system for resampling an input audio signal into an output audio signal, the system comprising:

• a processing unit configured to determine a current output sample of the output audio signal from one or more input samples of the input audio signal using a current subset of filter coefficients from a filter configured to reduce imaging and/or aliasing of the output audio signal;
• wherein the current subset of filter coefficients corresponds to a phase of a polyphase structure of the filter;
• and
• one or more look-up tables providing a mapping between phase indexes of different phases of the polyphase structure of the filter, which are to be used to determine different output samples, and phase indexes of directly preceding phases which are to be used to determine directly preceding output samples, respectively;
• and providing a mapping between phase indexes and respective subsets of filter coefficients from the filter;
• wherein the processing unit is configured to determine the current subset of filter coefficients based on a previous phase index for a previous output sample directly preceding the current output sample, using the one or more look-up tables.

A method for determining a sequence of phase indexes identifying a corresponding sequence of phases of a polyphase structure of a resampling filter used for determining a sequence of output samples of a resampled audio signal from a sequence of input samples of an input audio signal, the method comprising:

• selecting a first phase index from the sequence of phase indexes;
• increasing the first phase index by an upsampling factor L or by multiples of L, as long as the increased first phase index is smaller or equal to a downsampling factor M;
• and
• determining a second phase index which directly follows the first phase index in the sequence of phase indexes based on the increased first phase index.

A method for determining a sequence of phase indexes identifying a corresponding sequence of phases of a polyphase structure of a resampling filter used for determining a sequence of output samples of a resampled audio signal from a sequence of input samples of an input audio signal, the method comprising:

• determining a base vector comprising a sequence of ascending integers from 1 to an upsampling factor L;
• determining a concatenated vector from the base vector by concatenating the base vector M times, wherein M is a downsampling factor;
• and
• determining the sequence of phase indexes by selecting every Mth entry from the concatenated vector.