# US 2005/0159941 A1 · Method and apparatus for audio compression > Agents: this data is available as JSON from the patentgrep API and MCP server — see https://patentgrep.com/llms.txt - Number: US 2005/0159941 A1 - Document ID: US20050159941A1 - Status: Published application - Kind: A1 - Application number: 11/078,975 - Filed: 2005-03-11 - Published: 2005-07-21 - Earliest claimed: 2003-02-28 - Assignees: XVD Corporation - Inventors: Victor Kolesnik; Boris Kudryashov; Sergey Petrov; Evgeny Ovsyannikov; Boris Trojanovsky; Andrey Trofimov - Web page: https://patentgrep.com/patent/US20050159941A1 ## CPC - G10L 19/02: using spectral analysis, e.g. transform vocoders or subband vocoders - G10L: SPEECH ANALYSIS TECHNIQUES OR SPEECH SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING TECHNIQUES; SPEECH OR AUDIO CODING OR DECODING ## Abstract A method and apparatus for audio compression receives an audio signal. Transform coding is applied to the audio signal to generate a sequence of transform frequency coefficients. The sequence of transform frequency coefficients is partitioned into a plurality of non-uniform width frequency ranges and then zero value frequency coefficients are inserted at the boundaries of the non-uniform width frequency ranges. As a result, certain of the transform frequency coefficients that represent high frequencies are dropped. ## Claims ### Claim 1 A method for audio compression comprising: generating a plurality of frequency coefficients representing an audio signal; grouping the plurality of frequency coefficients into frequency ranges of non-uniform width; determining if a sound attack occurs in any one of the non-uniform width frequency ranges; and performing transform length switching separately on each of the frequency ranges based on determining occurrence of a sound attack. ### Claim 2 (depends on 1) The method of claim 1 further comprising stuffing zeros at the boundaries of the non-uniform width frequency ranges and dropping certain of the plurality of frequency coefficients that represent higher end frequencies. ### Claim 3 (depends on 2) The method of claim 2 wherein stuffing zeros at the boundaries comprises: insert zeros at the boundaries of the frequency ranges; and shifting those of the plurality of frequency coefficients that are displaced by the inserted zeros into the next frequency range. ### Claim 4 (depends on 1) The method of claim 1 further comprising separately performing transforms on each of the plurality of non-uniform width frequency ranges based on their width. ### Claim 5 (depends on 4) The method of claim 4 wherein the transforms are inverse modified discrete cosine transforms. ### Claim 6 (depends on 1) The method of claim 1 wherein the performed long and short transforms are modified discrete cosine transforms. ### Claim 7 A method for audio compression comprising: generating a plurality of non-uniform frequency subbands, each of the plurality of non-uniform frequency subbands including a set of one or more frequency coefficients, from an audio input signal; displacing those of the set of frequency coefficients at the boundary of each non-uniform frequency subband with zeros; separately normalizing the non-uniform frequency subbands, including the zeros; varying transform length applied to each of the plurality of non-uniform frequency subbands based on the detection of a sound attack within the plurality of non-uniform frequency subbands; and multiplexing the plurality of non-uniform frequency subbands. ### Claim 8 (depends on 7) The method of claim 7 wherein inverse modified discrete transform is applied to the plurality of non-uniform frequency subbands after normalizing. ### Claim 9 (depends on 7) The method of claim 7 wherein the varied transform is modified discrete cosine transform. ### Claim 10 A machine-readable medium having a set of instruction stored thereon, which when executed by a set of one or more processors causes the set of processors to perform the operations comprising: generating a plurality of frequency coefficients representing an audio signal; grouping the plurality of frequency coefficients into frequency ranges of non-uniform width; determining if a sound attack occurs in any one of the non-uniform width frequency ranges; and performing short transforms on those non-uniform frequency ranges that have a sound attack and long transforms on those non-uniform frequency ranges that do not have a sound attack. ### Claim 11 (depends on 10) The machine-readable medium of claim 10 further comprising stuffing zeros at the boundaries of the non-uniform width frequency ranges and dropping certain of the plurality of frequency coefficients that represent higher end frequencies. ### Claim 12 (depends on 11) The machine-readable medium of claim 11 wherein stuffing zeros at the boundaries comprises: insert zeros at the boundaries of the frequency ranges; and shifting those of the plurality of frequency coefficients that are displaced by the inserted zeros into the next frequency range. ### Claim 13 (depends on 10) The machine-readable medium of claim 10 further comprising separately performing transforms on each of the plurality of non-uniform width frequency ranges based on their width. ### Claim 14 (depends on 13) The machine-readable medium of claim 13 wherein the transforms are inverse modified discrete cosine transforms. ### Claim 15 (depends on 10) The machine-readable medium of claim 10 wherein the performed long and short transforms are modified discrete cosine transforms. ### Claim 16 A machine-readable medium having a set of instruction stored thereon, which when executed by a set of one or more processors causes the set of processors to perform the operations comprising: generating a plurality of non-uniform frequency subbands, each of the plurality of non-uniform frequency subbands including a set of one or more frequency coefficients, from an audio input signal; displacing those of the set of frequency coefficients at the boundary of each non-uniform frequency subband with zeros; separately normalizing the non-uniform frequency subbands, including the zeros; varying transform length applied to each of the plurality of non-uniform frequency subbands based on the detection of a sound attack within the plurality of non-uniform frequency subbands; and multiplexing the plurality of non-uniform frequency subbands. ### Claim 17 (depends on 16) The machine-readable medium of claim 16 wherein inverse modified discrete transform is applied to the plurality of non-uniform frequency subbands after normalizing. ### Claim 18 (depends on 16) The machine-readable medium of claim 16 wherein the varied transform is modified discrete cosine transform.