System aspects of an audio codec

Patent metadata

Field	Value
Publication number	US-2016196831-A1
Application number	US-201414916545-A
Country	US
Kind code	A1
Filing date	Sep 10, 2014
Priority date	Sep 12, 2013
Publication date	Jul 7, 2016
Grant date	—

Abstract

The present document relates to the design of anti-aliasing and/or anti-imaging filters for resamplers using rational resampling factors. In particular, the present document relates to a method for implementing such anti-aliasing and/or anti-imaging filters with reduced computational complexity. In addition, the present document relates to further aspects of an audio encoding and decoding system, such as the phase relation between the channels of a multi-channel audio signal and/or the structure of the bitstream of an encoded audio signal.

First claim

1 - 13 . (canceled)

14 . 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.

15 . The system of claim 14 , wherein:
the system comprises a phase look-up table providing the 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; the system comprises a filter look-up table providing the mapping between phase indexes and respective subsets of filter coefficients from the filter; the processing unit is configured to determine the current phase index based on the previous phase index for the previous output sample directly preceding the current output sample, using the phase look-up table; and the processing unit is configured to determine the current subset of filter coefficients based on the current phase index using the filter look-up table.

16 . The system of claim 15 , wherein:
the system is configured to resample the input audio signal in accordance to an upsampling factor L, with L being greater than one; the polyphase structure comprises L phases; and the phase look-up table provides for each of L phase indexes for the L phases a mapping to the phase index for the directly preceding phase.

17 . The system of claim 14 , wherein the system is configured to resample the input audio signal in accordance to a downsampling factor M, with M being greater than one.

18 . The system of claim 16 , wherein:
the filter comprises a total set of N filter coefficients; and the subsets of filter coefficients from the filter comprise N/L filter coefficients each.

19 . The system of claim 15 , wherein the phase look-up table is indicative of a sequence of phase indexes to be used to determine a corresponding sequence of output samples of the output audio signal.

20 . The system of claim 19 , wherein the processing unit is configured to determine the sequence of phase indexes and/or the phase look-up table based on the upsampling factor L and/or on the downsampling factor M.

21 . The system of claim 20 , wherein the processing unit is configured to:
determine a base vector comprising a sequence of ascending integers from 1 to L; determine a concatenated vector from the base vector by concatenating the base vector M times; and determine the sequence of phase indexes by selecting every M th entry from the concatenated vector.

22 . The system of claim 21 , wherein the processing unit is configured to:
select a first phase index from the sequence of phase indexes; increase the first phase index by L or multiples of L, as long as the increased first phase index is smaller or equal to M; and determine a second phase index which directly follows the first phase index in the sequence of phase indexes based on the increased first phase index.

23 . The system of claim 22 , wherein the processing unit is configured to determine the second phase index by subtracting M from the increased first phase index M, to yield an intermediate phase index.

24 . The system of claim 23 , wherein the processing unit is configured to determine the second phase index by subtracting the intermediate phase index from L+1.

25 . The system of claim 20 , wherein the processing unit is configured to determine the sequence of phase indexes by determining a difference between adjacent phase indexes from the sequence of phase indexes as Δ=[M MOD L], for one or more pairs of adjacent phase indexes.

26 . The system of claim 15 , wherein:
the system is configured to perform resampling in accordance to different upsampling factors L and/or in accordance to different downsampling factors M; the phase look-up table comprises a plurality of phase index-to-phase index mappings for a plurality of different resampling ratios L/M, respectively; and the filter look-up table comprises a plurality of phase index-to-subset of filter coefficients mappings for the plurality of different resampling ratios L/M, respectively.

27 . The system of claim 14 , wherein the subsets of filter coefficients for the different phases of the polyphase structure are mutually exclusive with respect to one another.

28 . The system of claim 14 , wherein:
the system comprises a combined phase/filter look-up table providing a mapping between phase indexes and respective subsets of filter coefficients from the filter; the phase indexes of the combined phase/filter look-up table are ordered in accordance to a sequence of phase indexes to be used to determine a corresponding sequence of output samples of the output audio signal.

29 . The system of claim 28 , wherein:
the system is configured to resample the input audio signal in accordance to an upsampling factor L, with L being greater than one; and the processing unit is configured to determine the current subset of filter coefficients based on the previous phase index for the previous output sample directly preceding the current output sample, using a MODULO L pointer into the combined phase/filter look-up table.

30 . 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.

31 . The method of claim 30 , further comprising determining the second phase index by subtracting M from the increased first phase index M, to yield an intermediate phase index.

32 . The method of claim 31 , further comprising determining the second phase index by subtracting the intermediate phase index from L+1.

33 . 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 seque

Assignees

• Dolby Lab Licensing Corp
• Dolby Int Ab

Inventors

• Groeschel Alexander
• Popp Jenns
• Wolters Martin
• Riedmiller Jeffrey
• Ward Michael
• Roeden Karl Jonas
• Hoerich Holger
• Linzmeier Karsten
• Friedrich Tobias

Classifications

• G10L19/008 Primary

  Multichannel audio signal coding or decoding using interchannel correlation to reduce redundancy, e.g. joint-stereo, intensity-coding or matrixing · CPC title

• G10L19/24 Primary

  Variable rate codecs, e.g. for generating different qualities using a scalable representation such as hierarchical encoding or layered encoding · CPC title

• G10L19/005

  Correction of errors induced by the transmission channel, if related to the coding algorithm · CPC title

• H04S2400/05

  Generation or adaptation of centre channel in multi-channel audio systems · CPC title

• H04S2400/03

  Aspects of down-mixing multi-channel audio to configurations with lower numbers of playback channels, e.g. 7.1 -> 5.1 (H04S2400/01 takes precedence) · CPC title