TWI618050B - 用於音訊處理系統中之訊號去相關的方法及設備 - Google Patents

用於音訊處理系統中之訊號去相關的方法及設備 Download PDF

Info

Publication number
TWI618050B
TWI618050B TW103101428A TW103101428A TWI618050B TW I618050 B TWI618050 B TW I618050B TW 103101428 A TW103101428 A TW 103101428A TW 103101428 A TW103101428 A TW 103101428A TW I618050 B TWI618050 B TW I618050B
Authority
TW
Taiwan
Prior art keywords
audio data
decorrelation
channel
audio
information
Prior art date
Application number
TW103101428A
Other languages
English (en)
Chinese (zh)
Other versions
TW201443877A (zh
Inventor
費南 梅寇特
顏冠傑
葛蘭特 大衛森
馬修 費勒斯
馬克 凡登
維瓦克 庫瑪
Original Assignee
杜比實驗室特許公司
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by 杜比實驗室特許公司 filed Critical 杜比實驗室特許公司
Publication of TW201443877A publication Critical patent/TW201443877A/zh
Application granted granted Critical
Publication of TWI618050B publication Critical patent/TWI618050B/zh

Links

Classifications

    • GPHYSICS
    • G10MUSICAL INSTRUMENTS; ACOUSTICS
    • G10LSPEECH ANALYSIS TECHNIQUES OR SPEECH SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING TECHNIQUES; SPEECH OR AUDIO CODING OR DECODING
    • G10L19/00Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis
    • G10L19/008Multichannel audio signal coding or decoding using interchannel correlation to reduce redundancy, e.g. joint-stereo, intensity-coding or matrixing
    • GPHYSICS
    • G10MUSICAL INSTRUMENTS; ACOUSTICS
    • G10LSPEECH ANALYSIS TECHNIQUES OR SPEECH SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING TECHNIQUES; SPEECH OR AUDIO CODING OR DECODING
    • G10L19/00Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis
    • G10L19/02Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis using spectral analysis, e.g. transform vocoders or subband vocoders
    • GPHYSICS
    • G10MUSICAL INSTRUMENTS; ACOUSTICS
    • G10LSPEECH ANALYSIS TECHNIQUES OR SPEECH SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING TECHNIQUES; SPEECH OR AUDIO CODING OR DECODING
    • G10L19/00Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis
    • G10L19/04Speech or audio signals analysis-synthesis techniques for redundancy reduction, e.g. in vocoders; Coding or decoding of speech or audio signals, using source filter models or psychoacoustic analysis using predictive techniques
    • G10L19/06Determination or coding of the spectral characteristics, e.g. of the short-term prediction coefficients
    • GPHYSICS
    • G10MUSICAL INSTRUMENTS; ACOUSTICS
    • G10LSPEECH ANALYSIS TECHNIQUES OR SPEECH SYNTHESIS; SPEECH RECOGNITION; SPEECH OR VOICE PROCESSING TECHNIQUES; SPEECH OR AUDIO CODING OR DECODING
    • G10L25/00Speech or voice analysis techniques not restricted to a single one of groups G10L15/00 - G10L21/00
    • G10L25/03Speech or voice analysis techniques not restricted to a single one of groups G10L15/00 - G10L21/00 characterised by the type of extracted parameters
    • G10L25/06Speech or voice analysis techniques not restricted to a single one of groups G10L15/00 - G10L21/00 characterised by the type of extracted parameters the extracted parameters being correlation coefficients
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04SSTEREOPHONIC SYSTEMS 
    • H04S3/00Systems employing more than two channels, e.g. quadraphonic
    • H04S3/008Systems employing more than two channels, e.g. quadraphonic in which the audio signals are in digital form, i.e. employing more than two discrete digital channels
    • HELECTRICITY
    • H04ELECTRIC COMMUNICATION TECHNIQUE
    • H04SSTEREOPHONIC SYSTEMS 
    • H04S5/00Pseudo-stereo systems, e.g. in which additional channel signals are derived from monophonic signals by means of phase shifting, time delay or reverberation 

Landscapes

  • Engineering & Computer Science (AREA)
  • Physics & Mathematics (AREA)
  • Acoustics & Sound (AREA)
  • Signal Processing (AREA)
  • Multimedia (AREA)
  • Computational Linguistics (AREA)
  • Health & Medical Sciences (AREA)
  • Audiology, Speech & Language Pathology (AREA)
  • Human Computer Interaction (AREA)
  • Spectroscopy & Molecular Physics (AREA)
  • Mathematical Physics (AREA)
  • Stereophonic System (AREA)
  • Compression, Expansion, Code Conversion, And Decoders (AREA)
  • Telephonic Communication Services (AREA)
TW103101428A 2013-02-14 2014-01-15 用於音訊處理系統中之訊號去相關的方法及設備 TWI618050B (zh)

Applications Claiming Priority (2)

Application Number Priority Date Filing Date Title
US201361764837P 2013-02-14 2013-02-14
US61/764,837 2013-02-14

Publications (2)

Publication Number Publication Date
TW201443877A TW201443877A (zh) 2014-11-16
TWI618050B true TWI618050B (zh) 2018-03-11

Family

ID=50064800

Family Applications (1)

Application Number Title Priority Date Filing Date
TW103101428A TWI618050B (zh) 2013-02-14 2014-01-15 用於音訊處理系統中之訊號去相關的方法及設備

Country Status (11)

Country Link
US (1) US9830916B2 (enExample)
EP (1) EP2956933B1 (enExample)
JP (1) JP6038355B2 (enExample)
KR (1) KR102114648B1 (enExample)
CN (1) CN104995676B (enExample)
BR (1) BR112015018981B1 (enExample)
ES (1) ES2613478T3 (enExample)
IN (1) IN2015MN01954A (enExample)
RU (1) RU2614381C2 (enExample)
TW (1) TWI618050B (enExample)
WO (1) WO2014126682A1 (enExample)

Families Citing this family (25)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
IN2015MN01952A (enExample) * 2013-02-14 2015-08-28 Dolby Lab Licensing Corp
TWI618050B (zh) 2013-02-14 2018-03-11 杜比實驗室特許公司 用於音訊處理系統中之訊號去相關的方法及設備
US9830917B2 (en) 2013-02-14 2017-11-28 Dolby Laboratories Licensing Corporation Methods for audio signal transient detection and decorrelation control
TWI640843B (zh) * 2014-04-02 2018-11-11 美商克萊譚克公司 用於產生遮罩之高密度對位映圖的方法、系統及電腦程式產品
EP3067887A1 (en) 2015-03-09 2016-09-14 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. Audio encoder for encoding a multichannel signal and audio decoder for decoding an encoded audio signal
EP3179744B1 (en) * 2015-12-08 2018-01-31 Axis AB Method, device and system for controlling a sound image in an audio zone
CN105702263B (zh) * 2016-01-06 2019-08-30 清华大学 语音重放检测方法和装置
CN105931648B (zh) * 2016-06-24 2019-05-03 百度在线网络技术(北京)有限公司 音频信号解混响方法和装置
CN107895580B (zh) * 2016-09-30 2021-06-01 华为技术有限公司 一种音频信号的重建方法和装置
EP3734998B1 (en) * 2016-11-23 2022-11-02 Telefonaktiebolaget LM Ericsson (publ) Method and apparatus for adaptive control of decorrelation filters
US10979844B2 (en) * 2017-03-08 2021-04-13 Dts, Inc. Distributed audio virtualization systems
US10019981B1 (en) 2017-06-02 2018-07-10 Apple Inc. Active reverberation augmentation
EP3573058B1 (en) * 2018-05-23 2021-02-24 Harman Becker Automotive Systems GmbH Dry sound and ambient sound separation
CN111107024B (zh) * 2018-10-25 2022-01-28 航天科工惯性技术有限公司 时间与频率混合编码的防错解码方法
CN109557509B (zh) * 2018-11-23 2020-08-11 安徽四创电子股份有限公司 一种用于改善脉间干扰的双脉冲信号合成器
CN109672946B (zh) * 2019-02-15 2023-12-15 深圳市昊一源科技有限公司 一种无线通话系统、转发设备、终端设备及转发方法
US11195541B2 (en) * 2019-05-08 2021-12-07 Samsung Electronics Co., Ltd Transformer with gaussian weighted self-attention for speech enhancement
CN110267064B (zh) * 2019-06-12 2021-11-12 百度在线网络技术(北京)有限公司 音频播放状态处理方法、装置、设备及存储介质
CN110740416B (zh) * 2019-09-27 2021-04-06 广州励丰文化科技股份有限公司 一种音频信号处理方法及装置
CN110740404B (zh) * 2019-09-27 2020-12-25 广州励丰文化科技股份有限公司 一种音频相关性的处理方法及音频处理装置
WO2022074202A2 (en) 2020-10-09 2022-04-14 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. Apparatus, method, or computer program for processing an encoded audio scene using a parameter smoothing
AU2021357840B2 (en) 2020-10-09 2024-06-27 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. Apparatus, method, or computer program for processing an encoded audio scene using a bandwidth extension
EP4443911A4 (en) * 2021-12-03 2025-02-19 Beijing Xiaomi Mobile Software Co., Ltd. STEREO AUDIO SIGNAL PROCESSING METHOD, AND DEVICE/STORAGE MEDIUM/APPARATUS
GB2630112A (en) * 2023-05-17 2024-11-20 Sony Interactive Entertainment Europe Ltd A method for decorrelating a set of simulated audio signals
WO2025160833A1 (zh) * 2024-01-31 2025-08-07 北京小米移动软件有限公司 编解码方法、装置以及存储介质

Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2006008697A1 (en) * 2004-07-14 2006-01-26 Koninklijke Philips Electronics N.V. Audio channel conversion
WO2006026452A1 (en) * 2004-08-25 2006-03-09 Dolby Laboratories Licensing Corporation Multichannel decorrelation in spatial audio coding
EP2144229A1 (en) * 2008-07-11 2010-01-13 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. Efficient use of phase information in audio encoding and decoding

Family Cites Families (65)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
GB8308843D0 (en) 1983-03-30 1983-05-11 Clark A P Apparatus for adjusting receivers of data transmission channels
CA1321645C (en) 1988-09-28 1993-08-24 Akira Ichikawa Method and system for voice coding based on vector quantization
EP0976306A1 (en) 1998-02-13 2000-02-02 Koninklijke Philips Electronics N.V. Surround sound reproduction system, sound/visual reproduction system, surround signal processing unit and method for processing an input surround signal
US6175631B1 (en) 1999-07-09 2001-01-16 Stephen A. Davis Method and apparatus for decorrelating audio signals
US7218665B2 (en) 2003-04-25 2007-05-15 Bae Systems Information And Electronic Systems Integration Inc. Deferred decorrelating decision-feedback detector for supersaturated communications
SE0301273D0 (sv) 2003-04-30 2003-04-30 Coding Technologies Sweden Ab Advanced processing based on a complex-exponential-modulated filterbank and adaptive time signalling methods
BRPI0508343B1 (pt) 2004-03-01 2018-11-06 Dolby Laboratories Licensing Corp método para decodificar m canais de áudio codificados representando n canais de áudio e método para codificar n canais de áudio de entrada em m canais de áudio codificados.
US20090299756A1 (en) 2004-03-01 2009-12-03 Dolby Laboratories Licensing Corporation Ratio of speech to non-speech audio such as for elderly or hearing-impaired listeners
BRPI0509108B1 (pt) * 2004-04-05 2019-11-19 Koninklijke Philips Nv método para codificar uma pluralidade de sinais de entrada, codificador para codificar uma pluralidade de sinais de entrada, método de decodificar dados, e decodificador
SE0400998D0 (sv) 2004-04-16 2004-04-16 Cooding Technologies Sweden Ab Method for representing multi-channel audio signals
WO2006040727A2 (en) 2004-10-15 2006-04-20 Koninklijke Philips Electronics N.V. A system and a method of processing audio data to generate reverberation
SE0402649D0 (sv) 2004-11-02 2004-11-02 Coding Tech Ab Advanced methods of creating orthogonal signals
US7787631B2 (en) 2004-11-30 2010-08-31 Agere Systems Inc. Parametric coding of spatial audio with cues based on transmitted channels
EP1691348A1 (en) * 2005-02-14 2006-08-16 Ecole Polytechnique Federale De Lausanne Parametric joint-coding of audio sources
US7961890B2 (en) 2005-04-15 2011-06-14 Fraunhofer-Gesellschaft Zur Foerderung Der Angewandten Forschung, E.V. Multi-channel hierarchical audio coding with compact side information
MX2007015118A (es) 2005-06-03 2008-02-14 Dolby Lab Licensing Corp Aparato y metodo para codificacion de senales de audio con instrucciones de decodificacion.
JP5097702B2 (ja) 2005-07-14 2012-12-12 コーニンクレッカ フィリップス エレクトロニクス エヌ ヴィ オーディオエンコード及びデコード
JP4944029B2 (ja) 2005-07-15 2012-05-30 パナソニック株式会社 オーディオデコーダおよびオーディオ信号の復号方法
JP2009506372A (ja) 2005-08-30 2009-02-12 エルジー エレクトロニクス インコーポレイティド オーディオ信号をエンコーディング及びデコーディングするための装置とその方法
RU2383942C2 (ru) 2005-08-30 2010-03-10 ЭлДжи ЭЛЕКТРОНИКС ИНК. Способ и устройство для декодирования аудиосигнала
US7974713B2 (en) 2005-10-12 2011-07-05 Fraunhofer-Gesellschaft Zur Foerderung Der Angewandten Forschung E.V. Temporal and spatial shaping of multi-channel audio signals
US7536299B2 (en) 2005-12-19 2009-05-19 Dolby Laboratories Licensing Corporation Correlating and decorrelating transforms for multiple description coding systems
JP2007178684A (ja) * 2005-12-27 2007-07-12 Matsushita Electric Ind Co Ltd マルチチャンネルオーディオ復号装置
EP1979898B1 (en) 2006-01-19 2014-08-06 Lg Electronics Inc. Method and apparatus for processing a media signal
TW200742275A (en) 2006-03-21 2007-11-01 Dolby Lab Licensing Corp Low bit rate audio encoding and decoding in which multiple channels are represented by fewer channels and auxiliary information
PL1999997T3 (pl) 2006-03-28 2011-09-30 Fraunhofer Ges Forschung Udoskonalony sposób kształtowania sygnału podczas rekonstrukcji wielokanałowego sygnału audio
EP1845699B1 (en) 2006-04-13 2009-11-11 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. Audio signal decorrelator
US8379868B2 (en) 2006-05-17 2013-02-19 Creative Technology Ltd Spatial audio coding based on universal spatial cues
EP1883067A1 (en) 2006-07-24 2008-01-30 Deutsche Thomson-Brandt Gmbh Method and apparatus for lossless encoding of a source signal, using a lossy encoded data stream and a lossless extension data stream
WO2008032255A2 (en) 2006-09-14 2008-03-20 Koninklijke Philips Electronics N.V. Sweet spot manipulation for a multi-channel signal
RU2406166C2 (ru) 2007-02-14 2010-12-10 ЭлДжи ЭЛЕКТРОНИКС ИНК. Способы и устройства кодирования и декодирования основывающихся на объектах ориентированных аудиосигналов
DE102007018032B4 (de) 2007-04-17 2010-11-11 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. Erzeugung dekorrelierter Signale
US8015368B2 (en) 2007-04-20 2011-09-06 Siport, Inc. Processor extensions for accelerating spectral band replication
US8515759B2 (en) 2007-04-26 2013-08-20 Dolby International Ab Apparatus and method for synthesizing an output signal
TWI527473B (zh) * 2007-06-08 2016-03-21 杜比實驗室特許公司 用以獲得環繞音效音訊頻道之方法、適於執行該方法之裝置、及相關電腦程式
US8046214B2 (en) 2007-06-22 2011-10-25 Microsoft Corporation Low complexity decoder for complex transform coding of multi-channel sound
US8064624B2 (en) 2007-07-19 2011-11-22 Fraunhofer-Gesellschaft Zur Foerderung Der Angewandten Forschung E.V. Method and apparatus for generating a stereo signal with enhanced perceptual quality
US20100040243A1 (en) 2008-08-14 2010-02-18 Johnston James D Sound Field Widening and Phase Decorrelation System and Method
CN101842832B (zh) 2007-10-31 2012-11-07 松下电器产业株式会社 编码装置和解码装置
US9196258B2 (en) 2008-05-12 2015-11-24 Broadcom Corporation Spectral shaping for speech intelligibility enhancement
JP5326465B2 (ja) 2008-09-26 2013-10-30 富士通株式会社 オーディオ復号方法、装置、及びプログラム
TWI413109B (zh) 2008-10-01 2013-10-21 Dolby Lab Licensing Corp 用於上混系統之解相關器
EP2214162A1 (en) 2009-01-28 2010-08-04 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. Upmixer, method and computer program for upmixing a downmix audio signal
EP2214165A3 (en) 2009-01-30 2010-09-15 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. Apparatus, method and computer program for manipulating an audio signal comprising a transient event
ES2374486T3 (es) 2009-03-26 2012-02-17 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. Dispositivo y método para manipular una señal de audio.
US8497467B2 (en) 2009-04-13 2013-07-30 Telcordia Technologies, Inc. Optical filter control
CN103489449B (zh) 2009-06-24 2017-04-12 弗劳恩霍夫应用研究促进协会 音频信号译码器、提供上混信号表示型态的方法
GB2465047B (en) 2009-09-03 2010-09-22 Peter Graham Craven Prediction of signals
PT2510515E (pt) 2009-12-07 2014-05-23 Dolby Lab Licensing Corp Descodificação de fluxos de bits de codificação de áudio multicanal utilizando transformação híbrida adaptativa
EP2360681A1 (en) 2010-01-15 2011-08-24 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. Apparatus and method for extracting a direct/ambience signal from a downmix signal and spatial parametric information
TWI444989B (zh) 2010-01-22 2014-07-11 Dolby Lab Licensing Corp 針對改良多通道上混使用多通道解相關之技術
JP5299327B2 (ja) 2010-03-17 2013-09-25 ソニー株式会社 音声処理装置、音声処理方法、およびプログラム
EP2375409A1 (en) * 2010-04-09 2011-10-12 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. Audio encoder, audio decoder and related methods for processing multi-channel audio signals using complex prediction
BR112012025878B1 (pt) 2010-04-09 2021-01-05 Dolby International Ab sistema decodificador, sistema codificador, método de decodificação e método de codificação.
US9135922B2 (en) 2010-08-24 2015-09-15 Lg Electronics Inc. Method for processing audio signals, involves determining codebook index by searching for codebook corresponding to shape vector generated by using location information and spectral coefficients
TWI516138B (zh) 2010-08-24 2016-01-01 杜比國際公司 從二聲道音頻訊號決定參數式立體聲參數之系統與方法及其電腦程式產品
WO2012025283A1 (en) 2010-08-25 2012-03-01 Fraunhofer-Gesellschaft Zur Foerderung Der Angewandten Forschung E.V. Apparatus for generating a decorrelated signal using transmitted phase information
US8908874B2 (en) * 2010-09-08 2014-12-09 Dts, Inc. Spatial audio encoding and reproduction
EP2477188A1 (en) 2011-01-18 2012-07-18 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. Encoding and decoding of slot positions of events in an audio signal frame
MX2013010535A (es) 2011-03-18 2014-03-12 Koninkl Philips Electronics Nv Transmision de longitud de elemento de cuadro en la codificacion de audio.
CN102903368B (zh) * 2011-07-29 2017-04-12 杜比实验室特许公司 用于卷积盲源分离的方法和设备
PL2740222T3 (pl) 2011-08-04 2015-08-31 Dolby Int Ab Usprawniony stereofoniczny radiowy odbiornik FM poprzez użycie stereo parametrycznego
US8527264B2 (en) 2012-01-09 2013-09-03 Dolby Laboratories Licensing Corporation Method and system for encoding audio data with adaptive low frequency compensation
ES2549953T3 (es) 2012-08-27 2015-11-03 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. Aparato y método para la reproducción de una señal de audio, aparato y método para la generación de una señal de audio codificada, programa de ordenador y señal de audio codificada
TWI618050B (zh) 2013-02-14 2018-03-11 杜比實驗室特許公司 用於音訊處理系統中之訊號去相關的方法及設備

Patent Citations (3)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
WO2006008697A1 (en) * 2004-07-14 2006-01-26 Koninklijke Philips Electronics N.V. Audio channel conversion
WO2006026452A1 (en) * 2004-08-25 2006-03-09 Dolby Laboratories Licensing Corporation Multichannel decorrelation in spatial audio coding
EP2144229A1 (en) * 2008-07-11 2010-01-13 Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V. Efficient use of phase information in audio encoding and decoding

Also Published As

Publication number Publication date
JP2016510433A (ja) 2016-04-07
TW201443877A (zh) 2014-11-16
HK1213686A1 (en) 2016-07-08
WO2014126682A1 (en) 2014-08-21
CN104995676B (zh) 2018-03-30
EP2956933B1 (en) 2016-11-16
IN2015MN01954A (enExample) 2015-08-28
EP2956933A1 (en) 2015-12-23
BR112015018981B1 (pt) 2022-02-01
RU2015133287A (ru) 2017-02-21
BR112015018981A2 (pt) 2017-07-18
JP6038355B2 (ja) 2016-12-07
ES2613478T3 (es) 2017-05-24
CN104995676A (zh) 2015-10-21
KR20150106949A (ko) 2015-09-22
RU2614381C2 (ru) 2017-03-24
US20150380000A1 (en) 2015-12-31
KR102114648B1 (ko) 2020-05-26
US9830916B2 (en) 2017-11-28

Similar Documents

Publication Publication Date Title
TWI618050B (zh) 用於音訊處理系統中之訊號去相關的方法及設備
TWI618051B (zh) 用於利用估計之空間參數的音頻訊號增強的音頻訊號處理方法及裝置
JP6046274B2 (ja) 上方混合されたオーディオ信号のチャネル間コヒーレンスの制御方法
WO2014126688A1 (en) Methods for audio signal transient detection and decorrelation control
HK1213686B (en) Signal decorrelation in an audio processing system
HK1218674B (en) Audio signal enhancement using estimated spatial parameters
HK1213687B (en) Controlling the inter-channel coherence of upmixed audio signals
WO2014126684A1 (en) Time-varying filters for generating decorrelation signals