SIST EN 300 969 V7.0.1:2003
(Main)Digital cellular telecommunications system (Phase 2+) (GSM); Half rate speech; Half rate speech transcoding (GSM 06.20 version 7.0.1 Release 1998)
- Abstract
Upgrade from Phase 2+ to Release 1998
- Status
- Published
- Publication Date
- 30-Nov-2003
- Current Stage
- 6060 - National Implementation/Publication (Adopted Project)
- Start Date
- 01-Dec-2003
- Due Date
- 01-Dec-2003
- Completion Date
- 01-Dec-2003
- Mandate
- T-172
SIST EN 300 969 V7.0.1:2003 is the ETSI European Standard for GSM half rate speech transcoding, transposed by SIST. It specifies the speech codec for the Global System for Mobile communications (GSM) half rate channel and the test methods used to verify codec implementation. The standard is aimed at GSM Mobile Stations (MS) and Base Station Systems (BSS) that use the half rate speech traffic channel.
What does SIST EN 300 969 V7.0.1:2003 specify?
SIST EN 300 969 V7.0.1:2003 specifies the half rate speech codec for the GSM half rate channel and the methods used to test compliance with that codec. Clause 1 makes the requirements mandatory for MS and BSS that use the half rate traffic channel.
The document is organized around the codec function, the homing sequences used for bit-exact testing, and two normative annexes for the coded parameters and their transmission order over Abis.
| Part | What it covers |
|---|---|
| Clause 4 | Functional description of the encoder and decoder |
| Clause 5 | Homing sequences for encoder and decoder reset/testing |
| Annex A | Codec parameter description and frame bit allocation |
| Annex B | Order of occurrence of codec parameters over Abis |
| Annex C | Bibliography |
| Annex D | Change request history |
What are the key requirements of SIST EN 300 969 V7.0.1:2003?
The standard defines a frame-based GSM half rate codec with a 20 ms speech frame, 160 samples per frame at 8 kHz, and a basic coder rate of 5.6 kbps. Annex A shows that each frame is coded into 112 bits, which matters when designing frame handling, buffer sizes, and signaling.
Speech analysis and encoding path
Clause 4 describes an analysis-by-synthesis codec based on the VSELP (Vector-Sum Excited Linear Prediction) algorithm. The encoder first applies a high-pass filter that suppresses content below 120 Hz, then computes short-term spectral parameters, frame energy, and excitation parameters. In practice, implementers need to reproduce the same signal path to get matching speech parameters.
The encoder uses four voicing modes, MODE 0 to MODE 3. MODE 0 is unvoiced, while MODE 1 to MODE 3 use the long-term predictor and harmonic noise weighting. This matters because the mode changes both the coding structure and the excitation search.
Spectral parameter coding
Clause 4.1.3 to 4.1.7 describe the short-term analysis. The 10 reflection coefficients are vector-quantized in three segments, and the frame energy R0 is quantized to 32 levels. Soft interpolation may be used for the spectral parameters, with a frame-by-frame choice between interpolated and uninterpolated coefficients based on residual energy and filter stability.
Long-term predictor and excitation search
For voiced modes, the codec searches for the long-term predictor lag and the VSELP codevector together. The standard defines open-loop and closed-loop lag search, allowable lags from 21 to 142 samples, and fractional lag handling with interpolation. In practice, this is the core of pitch prediction and strongly affects speech quality.
Clause 4.1.9 adds harmonic noise weighting for MODE 1 to MODE 3. That filter reduces error near pitch harmonics, so the search favors excitation that sounds cleaner to the ear, not just numerically smaller.
Decoder and homing behavior
Clause 4.2 describes the decoder path: excitation generation, adaptive pitch prefiltering, synthesis filtering, adaptive spectral postfiltering, and automatic gain control. Clause 5 defines encoder and decoder homing frames so that the codec can be reset and checked in a bit-exact way. That is important for conformance testing and for remote reset procedures.
What terms does SIST EN 300 969 V7.0.1:2003 define?
- Adaptive codebook - The long-term filter state used as the pitch-related excitation memory.
- Long-term filter - The filter that generates the periodic component of the excitation in voiced speech.
- Soft interpolation - The frame-by-frame choice between interpolated and uninterpolated spectral coefficients.
- Harmonic noise weighting filter - A filter that weights error more lightly near pitch harmonics.
- Subframe - A 5 ms interval, equal to 40 samples at 8 kHz.
- VSELP codebook - The Vector-Sum Excited Linear Prediction codebook used to build excitation vectors from basis vectors.
- Homing frame - A special input pattern used to force the codec into a known state for testing or reset.
Who uses SIST EN 300 969 V7.0.1:2003?
GSM handset and base station manufacturers use this standard when implementing the half rate speech codec in MS and BSS equipment. Codec developers use it to match the required encoder and decoder behavior, including parameter coding, lag search, and postfiltering.
Test laboratories and quality teams use Clause 5 and the test-sequence references to verify bit-exact behavior and reset handling. Network equipment engineers use Annex B when handling the codec parameter order over Abis.
What changed in SIST EN 300 969 V7.0.1:2003 from the previous edition?
Annex D records a version update to 7.0.1 for publication. The change history also shows earlier Release 1996, Release 1997, and Release 1998 milestones for the same family of documents.
Which standards are used with SIST EN 300 969 V7.0.1:2003?
| Reference | What it contributes |
|---|---|
| GSM 06.02 | Half rate speech processing functions |
| GSM 06.06 | ANSI-C code for the GSM half rate speech codec |
| GSM 06.07 | Test sequences for the GSM half rate speech codec |
The foreword also names related half rate speech traffic-channel parts in the same series: GSM 06.21, GSM 06.22, GSM 06.41 and GSM 06.42.
What does the SIST EN 300 969 V7.0.1:2003 document contain?
The document contains the encoder and decoder algorithms, including the high-pass filter, spectral analysis, lag search, codebook search, gain quantization, and decoder postfiltering. It also includes homing procedures for exact testing and reset behavior.
Annex A provides the frame parameter map, including bit allocations for MODE, R0, LPC segments, LAG fields, CODE fields, and GSP0 fields. Annex B gives the bit order over Abis for both MODE 0 and voiced modes, which is useful when building or checking signaling interfaces.
The body of Clause 4 includes block diagrams, formulas, and step-by-step procedures for FLAT, AFLAT, open-loop and closed-loop lag search, and harmonic noise weighting. Those details are used for implementation, debugging, and conformance-style verification.
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Frequently Asked Questions
SIST EN 300 969 V7.0.1:2003 is a standard published by the Slovenian Institute for Standardization (SIST). Its full title is "Digital cellular telecommunications system (Phase 2+) (GSM); Half rate speech; Half rate speech transcoding (GSM 06.20 version 7.0.1 Release 1998)". This standard covers: Upgrade from Phase 2+ to Release 1998
Upgrade from Phase 2+ to Release 1998
SIST EN 300 969 V7.0.1:2003 is classified under the following ICS (International Classification for Standards) categories: 33.070.50 - Global System for Mobile Communication (GSM). The ICS classification helps identify the subject area and facilitates finding related standards.
SIST EN 300 969 V7.0.1:2003 is associated with the following European legislation: Standardization Mandates: T-172. When a standard is cited in the Official Journal of the European Union, products manufactured in conformity with it benefit from a presumption of conformity with the essential requirements of the corresponding EU directive or regulation.
SIST EN 300 969 V7.0.1:2003 is available in PDF format for immediate download after purchase. The document can be added to your cart and obtained through the secure checkout process. Digital delivery ensures instant access to the complete standard document.
Standards Content (Sample)
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.Digital cellular telecommunications system (Phase 2+) (GSM); Half rate speech; Half rate speech transcoding (GSM 06.20 version 7.0.1 Release 1998)33.070.50Globalni sistem za mobilno telekomunikacijo (GSM)Global System for Mobile Communication (GSM)ICS:Ta slovenski standard je istoveten z:EN 300 969 Version 7.0.1SIST EN 300 969 V7.0.1:2003en01-december-2003SIST EN 300 969 V7.0.1:2003SLOVENSKI
STANDARD
ETSIEN300969V7.0.1(2000-01)EuropeanStandard(Telecommunicationsseries)Digitalcellulartelecommunicationssystem(Phase2+);Halfratespeech;Halfratespeechtranscoding(GSM06.20version7.0.1Release1998)GLOBALSYSTEMFORMOBILECOMMUNICATIONSRSIST EN 300 969 V7.0.1:2003
ETSIETSIEN300969V7.0.1(2000-01)2(GSM06.20version7.0.1Release1998)ReferenceREN/SMG-110620Q7KeywordsDigitalcellulartelecommunicationssystem,GlobalSystemforMobilecommunications(GSM),CODEC,GSM,speechETSIPostaladdressF-06921SophiaAntipolisCedex-FRANCEOfficeaddress650RoutedesLucioles-SophiaAntipolisValbonne-FRANCETel.:+33492944200Fax:+33493654716SiretN°34862356200017-NAF742CAssociationàbutnonlucratifenregistréeàlaSous-PréfecturedeGrasse(06)N°7803/88Internetsecretariat@etsi.frIndividualcopiesofthisETSIdeliverablecanbedownloadedfromhttp://www.etsi.orgIfyoufinderrorsinthepresentdocument,sendyourcommentto:editor@etsi.frImportantnoticeThisETSIdeliverablemaybemadeavailableinmorethanoneelectronicversionorinprint.Inanycaseofexistingorperceiveddifferenceincontentsbetweensuchversions,thereferenceversionisthePortableDocumentFormat(PDF).Incaseofdispute,thereferenceshallbetheprintingonETSIprintersofthePDFversionkeptonaspecificnetworkdrivewithinETSISecretariat.CopyrightNotificationNopartmaybereproducedexceptasauthorizedbywrittenpermission.Thecopyrightandtheforegoingrestrictionextendtoreproductioninallmedia.©EuropeanTelecommunicationsStandardsInstitute2000.Allrightsreserved.SIST EN 300 969 V7.0.1:2003
ETSIETSIEN300969V7.0.1(2000-01)3(GSM06.20version7.0.1Release1998)ContentsIntellectualPropertyRights.5Foreword.51Scope.72References.73Definitions,symbolsandabbreviations.73.1Definitions.73.2Symbols.93.3Abbreviations.104FunctionaldescriptionoftheGSMhalfratespeechcodec.114.1GSMhalfratespeechencoder.114.1.1High-passfilter.134.1.2Segmentation.144.1.3FixedPointLatticeTechnique(FLAT).144.1.4Spectralquantization.154.1.4.1AutocorrelationFixedPointLatticeTechnique(AFLAT).154.1.5Frameenergycalculationandquantization.174.1.6Softinterpolationofthespectralparameters.174.1.7Spectralnoiseweightingfiltercoefficients.184.1.8LongTermPredictorlagdetermination.194.1.8.1Openlooplongtermsearchinitialization.204.1.8.2Openlooplagsearch.214.1.8.3Framelagtrajectorysearch(Mode≠0).264.1.8.4Voicingmodeselection.284.1.8.5Closedlooplagsearch.284.1.9Harmonicnoiseweighting.294.1.10Codesearchalgorithm.314.1.10.1Decorrelationoffilteredbasisvectors.324.1.10.2Fastsearchtechnique.334.1.11Multimodegainvectorquantization.344.1.11.1CodingGSandP0.344.2GSMhalfratespeechdecoder.374.2.1Excitationgeneration.374.2.2Adaptivepitchprefilter.384.2.3SynthesisFilter.384.2.4Adaptivespectralpostfilter.384.2.5Updatingdecoderstates.405Homingsequences.405.1Functionaldescription.405.2Definitions.405.3Encoderhoming.405.4Decoderhoming.415.5Encoderhomestate.415.6Decoderhomestate.41AnnexA(normative):Codecparameterdescription.42A.1Codecparameterdescription.42A.1.1MODE.42A.1.2R0.42A.1.3LPC1-LPC3.43A.1.4LAG_1-LAG_4.43A.1.5CODEx_1-CODEx_4.43A.1.6GSP0_1-GSP0_4.43SIST EN 300 969 V7.0.1:2003
ETSIETSIEN300969V7.0.1(2000-01)4(GSM06.20version7.0.1Release1998)A.2Basiccoderparameters.43AnnexB(normative):OrderofoccurrenceofthecodecparametersoverAbis.44AnnexC(informative):Bibliography.45AnnexD(informative):ChangeRequestHistory.46History.47SIST EN 300 969 V7.0.1:2003
ETSIETSIEN300969V7.0.1(2000-01)5(GSM06.20version7.0.1Release1998)IntellectualPropertyRightsIPRsessentialorpotentiallyessentialtothepresentdocumentmayhavebeendeclaredtoETSI.TheinformationpertainingtotheseessentialIPRs,ifany,ispubliclyavailableforETSImembersandnon-members,andcanbefoundinSR000314:"IntellectualPropertyRights(IPRs);Essential,orpotentiallyEssential,IPRsnotifiedtoETSIinrespectofETSIstandards",whichisavailablefromtheETSISecretariat.LatestupdatesareavailableontheETSIWebserver(http://www.etsi.org/ipr).PursuanttotheETSIIPRPolicy,noinvestigation,includingIPRsearches,hasbeencarriedoutbyETSI.NoguaranteecanbegivenastotheexistenceofotherIPRsnotreferencedinSR000314(ortheupdatesontheETSIWebserver)whichare,ormaybe,ormaybecome,essentialtothepresentdocument.ForewordThisEuropeanStandard(Telecommunicationsseries)hasbeenproducedbytheSpecialMobileGroup(SMG).ThepresentdocumentspecifiesthespeechcodectobeusedfortheGSMhalfratechannelforthedigitalcellulartelecommunicationssystem.Thepresentdocumentispartofaseriescoveringthehalfratespeechtrafficchannelsasdescribedbelow:GSM06.02"Digitalcellulartelecommunicationssystem(Phase2+);Halfratespeech;Halfratespeechprocessingfunctions".GSM06.06"Digitalcellulartelecommunicationssystem(Phase2+);Halfratespeech;ANSI-CcodefortheGSMhalfratespeechcodec".GSM06.07"Digitalcellulartelecommunicationssystem(Phase2+);Halfratespeech;TestsequencesfortheGSMhalfratespeechcodec".GSM06.20"Digitalcellulartelecommunicationssystem(Phase2+);Halfratespeech;Halfratespeechtranscoding".GSM06.21"Digitalcellulartelecommunicationssystem(Phase2+);Halfratespeech;Substitutionandmutingoflostframesforhalfratespeechtrafficchannels".GSM06.22"Digitalcellulartelecommunicationssystem(Phase2+);Halfratespeech;Comfortnoiseaspectsforhalfratespeechtrafficchannels".GSM06.41"Digitalcellulartelecommunicationssystem(Phase2+);Halfratespeech;DiscontinuousTransmission(DTX)forhalfratespeechtrafficchannels".GSM06.42"Digitalcellulartelecommunicationssystem(Phase2+);Halfratespeech;VoiceActivityDetector(VAD)forhalfratespeechtrafficchannels".ThecontentsofthepresentdocumentissubjecttocontinuingworkwithinSMGandmaychangefollowingformalSMGapproval.ShouldSMGmodifythecontentsofthepresentdocumentitwillbere-releasedwithanidentifyingchangeofreleasedateandanincreaseinversionnumberasfollows:Version7.x.ywhere:7indicatesRelease1998ofGSMPhase2+.xtheseconddigitisincrementedforallchangesofsubstance,i.e.technicalenhancements,corrections,updates,etc.ythethirddigitisincrementedwheneditorialonlychangeshavebeenincorporatedinthespecification.SIST EN 300 969 V7.0.1:2003
ETSIETSIEN300969V7.0.1(2000-01)6(GSM06.20version7.0.1Release1998)NationaltranspositiondatesDateofadoptionofthisEN:31December1999DateoflatestannouncementofthisEN(doa):31March2000DateoflatestpublicationofnewNationalStandardorendorsementofthisEN(dop/e):30September2000DateofwithdrawalofanyconflictingNationalStandard(dow):30September2000SIST EN 300 969 V7.0.1:2003
ETSIETSIEN300969V7.0.1(2000-01)7(GSM06.20version7.0.1Release1998)1ScopeThepresentdocumentspecifiesthespeechcodectobeusedfortheGSMhalfratechannel.Italsospecifiesthetestmethodstobeusedtoverifythatthecodecimplementationcomplieswiththepresentdocument.TherequirementsaremandatoryforthecodectobeusedeitherinGSMMobileStations(MS)sorBaseStationSystems(BSS)sthatutilizethehalfrateGSMspeechtrafficchannel.2ReferencesThefollowingdocumentscontainprovisionswhich,throughreferenceinthistext,constituteprovisionsofthepresentdocument.•Referencesareeitherspecific(identifiedbydateofpublication,editionnumber,versionnumber,etc.)ornon-specific.•Foraspecificreference,subsequentrevisionsdonotapply.•Foranon-specificreference,thelatestversionapplies.•Anon-specificreferencetoanETSshallalsobetakentorefertolaterversionspublishedasanENwiththesamenumber.•ForthisRelease1998document,referencestoGSMdocumentsareforRelease1998versions(version7.x.y).[1]GSM06.02:"Digitalcellulartelecommunicationssystem(Phase2+);Halfratespeech;Halfratespeechprocessingfunctions".[2]GSM06.06:"Digitalcellulartelecommunicationssystem(Phase2+);Halfratespeech;ANSI-CcodefortheGSMhalfratespeechcodec".[3]GSM06.07:"Digitalcellulartelecommunicationssystem(Phase2+);Halfratespeech;TestsequencesfortheGSMhalfratespeechcodec".3Definitions,symbolsandabbreviations3.1DefinitionsForthepurposesofthepresentdocument,thefollowingtermsanddefinitionsapply.adaptivecodebook:Theadaptivecodebookisderivedfromthelongtermfilterstate.Thelagvaluecanbeviewedasanindexintotheadaptivecodebook.adaptivepitchprefilter:IntheGSMhalfratespeechdecoder,thisfilterisappliedtotheexcitationsignaltoenhancetheperiodicityofthereconstructedspeech.Notethatthisisdonepriortotheapplicationoftheshorttermfilter.adaptivespectralpostfilter:IntheGSMhalfratespeechdecoder,thisfilterisappliedtotheoutputoftheshorttermfiltertoenhancetheperceptualqualityofthereconstructedspeech.allowablelags:ThesetoflagvalueswhichmaybecodedbytheGSMhalfratespeechencoderandtransmittedtotheGSMhalfratespeechdecoder.Thissetcontainsbothintegerandfractionalvalues(seetable3).analysiswindow:Foreachframe,theshorttermfiltercoefficientsarecomputedusingthehighpassfilteredspeechsampleswithintheanalysiswindow.Theanalysiswindowis170samplesinlength,andiscenteredaboutthelast100samplesintheframe.basisvectors:AsetofM,M1,orM2vectorsoflengthNsusedtogeneratetheVSELPcodebookvectors.Thesevectorsarenotnecessarilyorthogonal.SIST EN 300 969 V7.0.1:2003
ETSIETSIEN300969V7.0.1(2000-01)8(GSM06.20version7.0.1Release1998)closedlooplagsearch:Aprocessofdeterminingthenearoptimallagvaluefromtheweightedinputspeechandthelongtermfilterstate.closedlooplagtrajectory:Foragivenframe,thesequenceofnearoptimallagvalueswhoseelementscorrespondtoeachofthefoursubframesasdeterminedbytheclosedlooplagsearch.codebook:Asetofvectorsusedinavectorquantizer.Codeword(ORCode):AnM,M1,orM2bitsymbolindicatingthevectortobeselectedfromaVSELPcodebook.Delta(LAG)code:Afourbitcodeindicatingthechangeinlagvalueforasubframerelativetotheprevioussubframe'scodedlag.Forframesinwhichthelongtermpredictorisenabled(MODE1,2,or3),thelagforsubframe1isindependentlycodedusingeightbits,anddeltacodesareusedforsubframes2,3,and4.directformcoefficients:Oneoftheformatsforstoringtheshorttermfilterparameters.Allfilterswhichareusedtomodifyspeechsamplesusedirectformcoefficients.fractionallags:Asetoflagvalueshavingsub-sampleresolution.NotethatnoteveryfractionallagvalueconsideredintheGSMhalfratespeechencoderisanallowablelagvalue.frame:Atimeintervalequalto20ms,or160samplesatan8kHzsamplingrate.harmonicnoiseweightingfilter:Thisfilterexploitsthenoisemaskingpropertiesofthespectralpeakswhichoccuratharmonicsofthepitchfrequencybyweightingtheresidualerrorlessinregionsnearthepitchharmonicsandmoreinregionsawayfromthem.Notethatthisfilterisonlyusedwhenthelongtermfilterisenabled(MODE=1,2or3).highpassfilter:Thisfilterisusedtode-emphasizethelowfrequencycomponentsoftheinputspeechsignal.integerlags:Asetoflagvalueshavingwholesampleresolution.interpolatingfilter:AnFIRfilterusedtoestimatesub-sampleresolutionsamples,givenaninputsampledwithintegersampleresolution.lag:Thelongtermfilterdelay.Thisistypicallythepitchperiod,oramultipleorsub-multipleofit.longtermfilter:Thisfilterisusedtogeneratetheperiodiccomponentintheexcitationforthecurrentsubframe.ThisfilterisonlyenabledforMODE=1,2or3.LPCcoefficients:LinearPredictiveCoding(LPC)coefficientsisagenericdescriptivetermfordescribingtheshorttermfiltercoefficients.openlooplagsearch:Aprocessofestimatingthenearoptimallagdirectlyfromtheweightedspeechinput.Thisisdonetonarrowtherangeoflagvaluesoverwhichtheclosedlooplagsearchshallbeperformed.openlooplagtrajectory:Foragivenframe,thesequenceofnearoptimallagvalueswhoseelementscorrespondtothefoursubframesasdeterminedbytheopenlooplagsearch.reflectioncoefficients:Analternativerepresentationoftheinformationcontainedintheshorttermfilterparameters.residual:Theoutputsignalresultingfromaninversefilteringoperation.shorttermfilter:Thisfilterintroduces,intotheexcitationsignal,shorttermcorrelationwhichmodelstheimpulseresponseofthevocaltract.softinterpolation:Aprocesswhereinadecisionismadeforeachframetouseeitherinterpolatedoruninterpolatedshorttermfilterparametersforthefoursubframesinthatframe.softinterpolationbit:Aonebitcodeindicatingwhetherornotinterpolationoftheshorttermparametersistobeusedinthecurrentframe.spectralnoiseweightingfilter:Thisfilterexploitsthenoisemaskingpropertiesoftheformants(vocaltractresonances)byweightingtheresidualerrorlessinregionsneartheformantfrequenciesandmoreinregionsawayfromthem.subframe:Atimeintervalequalto5ms,or40samplesatan8kHzsamplingrate.SIST EN 300 969 V7.0.1:2003
ETSIETSIEN300969V7.0.1(2000-01)9(GSM06.20version7.0.1Release1998)vectorquantization:Amethodofgroupingseveralparametersintoavectorandquantizingthemsimultaneously.GSP0vectorquantizer:Theprocessofvectorquantization,itsintermediateparameters(GSandP0)forthecodingoftheexcitationgainsβandγ.VSELPcodebook:Vector-SumExcitedLinearPredictive(VSELP)codebook,usedintheGSMhalfratespeechcoder,whereineachcodebookvectorisconstructedasalinearcombinationofthefixedbasisvectors.zeroinputresponse:Theoutputofafilterduetoallpastinputs,i.e.duetothepresentstateofthefilter,giventhataninputofzerosisapplied.zerostateresponse:Theoutputofafilterduetothepresentinput,giventhatnopastinputshavebeenapplied,i.e.giventhestateinformationinthefilterisallzeroes.3.2SymbolsForthepurposesofthepresentdocument,thefollowingsymbolsapply:A(z)Shorttermspectralfilter.αiTheLPCcoefficients.bL(n)Theoutputofthelongtermfilterstate(adaptivecodebook)forlagL.βThelongtermfiltercoefficient.C(z)Secondweightingfilter.e(n)Weightederrorsignalfj(i)Thecoefficientsofthejthphaseofthe10thorderinterpolatingfilterusedtoevaluatecandidatefractionallagvalues;irangesfrom0toPf-1.gj(i)Thecoefficientsofthejthphaseofthe6thorderinterpolatingfilterusedtointerpolateC'sandG'saswellasfractionallagsintheharmonicnoiseweighting;irangesfrom0toPg-1.γThegainappliedtothevector(s)selectedfromtheVSELPcodebook(s).HAM2bitcodeindicatingthevectortobeselectedfromthesecondVSELPcodebook(whenoperatinginmode0).IAMorM1bitcodeindicatingthevectortobeselectedfromoneofthetwofirstVSELPcodebooks.LThelongtermfilterlagvalue.Lmax142(samples),themaximumpossiblevalueforthelongtermfilterlag.Lmin21(samples),theminimumpossiblevalueforthelongtermfilterlag.M9,thenumberofbasisvectors,andthenumberofbitsinacodeword,fortheVSELPcodebookusedinmodes1,2,and3.M17,thenumberofbasisvectors,andthenumberofbitsinacodeword,forthefirstVSELPcodebookusedinmode0.M27,thenumberofbasisvectors,andthenumberofbitsinacodeword,forthesecondVSELPcodebookusedinmode0.MODEAtwobitcodeindicatingthemodeforthecurrentframe(seeannexA).NA170,thelengthoftheanalysiswindow.Thisisthenumberofhighpassfilteredspeechsamplesusedtocomputetheshorttermfilterparametersforeachframe.NF160,thenumberofsamplesperframe(atasamplingrateof8kHz).Np10,theshorttermfilterorder.Ns40,thenumberofsamplespersubframe(atasamplingrateof8kHz).P16,thenumberofbitsintheprequantizerforther1-r3vectorquantizer.P25,thenumberofbitsintheprequantizerforther4-r6vectorquantizer.P34,thenumberofbitsintheprequantizerforther7-r10vectorquantizer.PfTheorderofonephaseofaninterpolatingfilterusedtoevaluatecandidatefractionallagvalues.Pfequals10forj≠0andequalto1forj=0.PgTheorderofonephaseofaninterpolatingfilter,fj(n),usedtointerpolateC'sandG'saswellasfractionallagsintheharmonicnoiseweighting,Pgequals6.pitchThetimedurationbetweentheglottalpulseswhichresultwhenthevocalchordsvibrateduringspeechproduction.Q111,thenumberofbitsinther1-r3reflectioncoefficientvectorquantizer.Q29,thenumberofbitsinther4-r6reflectioncoefficientvectorquantizer.Q38,thenumberofbitsinther7-r10reflectioncoefficientvectorquantizer.SIST EN 300 969 V7.0.1:2003
ETSIETSIEN300969V7.0.1(2000-01)10(GSM06.20version7.0.1Release1998)R0Afivebitcodeusedtoindicatetheenergylevelinthecurrentframe.r(n)Thelongtermfilterstate(thehistoryoftheexcitationsignal);n<0rL(n)ThelongtermfilterstatewiththeadaptivecodebookoutputforlagLappended.s'(n)Synthesizedspeech.W(z)Spectralweightingfilter.λhnwTheharmonicnoiseweightingfiltercoefficient.ξTheadaptivepitchprefiltercoefficient.xCeilingfunction:thelargestintegerywherey
ETSIETSIEN300969V7.0.1(2000-01)11(GSM06.20version7.0.1Release1998)4FunctionaldescriptionoftheGSMhalfratespeechcodecTheGSMhalfratecodecusestheVSELP(Vector-SumExcitedLinearPrediction)algorithm.TheVSELPalgorithmisananalysis-by-synthesiscodingtechniqueandbelongstotheclassofspeechcodingalgorithmsknownasCELP(CodeExcitedLinearPrediction).TheGSMhalfratecodec'sencodingprocessisperformedona20msspeechframeatatime.Aspeechframeofthesampledspeechwaveformisreadandbasedonthecurrentwaveformandthepasthistoryofthewaveform,thecodecencoderderives18parametersthatdescribeit.Theparametersextractedaregroupedintothefollowingthreegeneralclasses:-energyparameters(R0andGSP0);-spectralparameters(LPCandINT_LPC);-excitationparameters(LAGandCODE).Theseparametersarequantizedinto112bitsfortransmissionasdescribedinannexAandtheirorderofoccurrenceoverAbisisgiveninannexB.TheGSMhalfratecodecisananalysis-by-synthesiscodec,thereforethespeechdecoderisprimarilyasubsetofthespeechencoder.Thequantizedparametersaredecodedandasyntheticexcitationisgeneratedusingtheenergyandexcitationparameters.Thesyntheticexcitationisthenfilteredtoprovidethespectralinformationresultinginthegenerationofthesynthesizedspeech(seefigure1).GSMhalfratespeechcodecSpeechencoderSpeechdecoderspeechtransmittedspeechparametersreceivedspeechparameterssynthesisedspeechFigure1:BlockdiagramoftheGSMhalfratespeechcodecTheANSI-CcodethatdescribestheGSMhalfratespeechcodecisgiveninGSM06.06[2]andthetestsequencesinGSM06.07[3](seeclause5forthecodechomingtestsequences).4.1GSMhalfratespeechencoderTheGSMhalfratespeechencoderusesananalysisbysynthesisapproachtodeterminethecodetousetorepresenttheexcitationforeachsubframe.ThecodebooksearchprocedureconsistsoftryingeachcodevectorasapossibleexcitationfortheCodeExcitedLinearPredictive(CELP)synthesizer.Thesynthesizedspeechs'(n)iscomparedagainsttheinputspeechandadifferencesignalisgenerated.Thisdifferencesignalisthenfilteredbyaspectralweightingfilter,W(z),(andpossiblyasecondweightingfilter,C(z))togenerateaweightederrorsignal,e(n).Thepowerine(n)iscomputed.Thecodevectorwhichgeneratestheminimumweightederrorpowerischosenasthecodevectorforthatsubframe.Thespectralweightingfilterservestoweighttheerrorspectrumbasedonperceptualconsiderations.Thisweightingfilterisafunctionofthespeechspectrumandcanbeexpressedintermsoftheαparametersoftheshortterm(spectral)filter.SIST EN 300 969 V7.0.1:2003
ETSIETSIEN300969V7.0.1(2000-01)12(GSM06.20version7.0.1Release1998)()WzzziiiNiiiNpp=−−−=−=1111αα~(1)Thecomputationoftheαicoefficientsisdescribedinsubclause4.1.7.ThesecondweightingfilterC(z),ifused,isaharmonicweightingfilterandisusedtocontroltheamountoferrorintheharmonicsofthespeechsignal.Iftheweightingfilter(s)aremovedtobothinputpathstothesubtracter,anequivalentconfigurationisobtainedasshowninfigure2.Σ( )2VSELPCodebookX_IγInputspeechs(n)y(n)y'(n)e(n)DetermineLPCcoefficientsβLtotalweightederrorLPC1LPC2LPC3R0INT_LPCMODELAG-1CODE_1LAG_2CODE_2LAG_3CODE_3LAG_4CODE_4GSP0-1GSP0_2GSP0_3GSP0_4W(z)C(z)FindMinimumoverLandallIB(z)H(z)C(z)βγfindoptimalgainsand.Figure2:BlockdiagramoftheGSMhalfratespeechencoder(MODE=1,2and3)HereH(z)isthecombinationofA(z),theshortterm(spectral)filter,andW(z),thespectralweightingfilter.ThesefiltersarecombinedsincethedenominatorofA(z)iscancelledbythenumeratorofW(z).SIST EN 300 969 V7.0.1:2003
ETSIETSIEN300969V7.0.1(2000-01)13(GSM06.20version7.0.1Release1998)()HzziiiNp=−−=111~α(2)Therearetwoapproachesthatcanbeusedforcalculatingthegain,γ.Thegaincanbedeterminedpriortocodebooksearchbasedonresidualenergy.Thisgainwouldthenbefixedforthecodebooksearch.Anotherapproachistooptimizethegainforeachcodevectorduringthecodebooksearch.Thecodevectorwhichyieldstheminimumweightederrorwouldbechosenanditscorrespondingoptimalgainwouldbeusedforγ.Thelatterapproachgenerallyyieldsbetterresultssincethegainisoptimizedforeachcodevector.Thisapproachalsoimpliesthatthegaintermneedstobeupdatedatthesubframerate.Theoptimalcodeandgainforthistechniquecanbecomputedasfollows:Theinputspeechisfirstfilteredbyahighpassfilterasdescribedinsubclause4.1.1.Theshorttermfilterparametersarecomputedfromthefilteredinputspeechonceperframe.Afastfixedpointcovariancelatticetechniqueisused.Subclauses4.1.3and4.1.4describesindetailhowtheshorttermparametersaredeterminedandquantized.Anoverallframeenergyisalsocomputedandcodedonceperframe.Onceperframe,oneofthefourvoicingmodesisselected.IfMODE≠0,thelongtermpredictorisusedandthelongtermpredictorlag,L,isupdatedatthesubframerate.LandaVSELPcodewordareselectedsequentially.Eachischosentominimizetheweightedmeansquareerror.Thelong-termfiltercoefficient,β,andthecodebookgain,γ,areoptimizedjointly.Subclause4.1.8describesthetechniqueforselectingfromamongthevoicingmodesand,ifoneofvoicedmodesischosen,determiningthelong-termfilterlag.Subclause4.1.10describesanefficienttechniqueforjointlyoptimizingβ,γandthecodewordselection.Subclause4.1.10alsoincludesthedescriptionofthefastVSELPcodebooksearchtechnique.Theβandγparametersaretransformedtoequivalentparametersusingtheframeenergyterm,andarevectorquantizedeverysubframe.Thecodingoftheframeenergyandtheβ andγparametersisdescribedinsubclause4.1.11.4.1.1High-passfilterThe13bitlinearPulseCodeModulated(PCM)inputspeech,x(n),isfilteredbyafourthorderpole-zerohighpassfilter.Thisfiltersuppressesthefrequencycomponentsoftheinputspeechwhicharebelow120Hz.Thefilterisimplementedasacascadeoftwosecond-orderInfiniteImpulseResponse(IIR)filters.Incorporatedintothefiltercoefficientsisagainof0,5.Thedifferenceequationforthefirstfilteris:()()()~~,,ynbxniaynjiijj=−+−==102112(3)where:b10=0,335052b11=-0,669983a11=0,926117b12=0,335052a12=-0,429413Thedifferenceequationforthesecondfilteris:()()()ynbyniaynjiijj=−+−==202212,,~(4)where:b20=0,335052b21=-0,669434a21=0,965332b22=0,335052a22=-0,469513SIST EN 300 969 V7.0.1:2003
ETSIETSIEN300969V7.0.1(2000-01)14(GSM06.20version7.0.1Release1998)4.1.2SegmentationAsamplebuffercontainingtheprevious195inputhighpassfilteredspeechsamples,y(n),isshiftedsothattheoldest160samplesareshiftedoutwhilethenext160inputsamplesareshiftedin.Theoldest160samplesinthebuffercorrespondtothenextframeofsamplestobeencoded.Theanalysisintervalcomprisesthemostrecent170samplesinthebuffer.Thesamplesinthebufferarelabelledass(n)where0≤n≤194ands(0)isthefirst(oldest)sample.4.1.3FixedPointLatticeTechnique(FLAT)Letrjrepresentthejthreflectioncoefficient.TheFLATalgorithmforthedeterminationofthereflectioncoefficientsisstatedasfollows:STEP1Computethecovariance(autocorrelation)matrixfromtheinputspeech:()()()φiksnisnknNNpA,=+−+−=24240≤i,k≤Np(5)STEP2Theφ(i,k)arrayismodifiedbywindowing()()()φφ',,ikikwik=−0≤i,k≤Np(6)STEP3()()Fikik0,',=φ0≤i,k≤Np-1(7)()()Bikik011,',=++φ0≤i,k≤Np-1(8)()()Cikik01,',=+φ0≤i,k≤Np-1(9)STEP4setj=1STEP5Computerj()()()()()()rCCNjNjFBFNjNjBNjNjjjjppjjjppjpp=−+−−++−−+−−−−−−−−2000000111111,,,,,,(10)STEP6Ifj=NPthendone.STEP7UpdateFj(i,k),Bj(i,k),Cj(i,k)0≤i,k≤NP-j-1()()()()()()FikFikrCikCkirBikjjjjjjj,,,,,=+++−−−−11121(11)()()()()()()BikBikrCikCkirFikjjjjjjj,,,,,=+++++++++++−−−−1112111111111,(12)()()()()()()CikCikrBikFikrCkijjjjjjj,,,,,=+++++++−−−−111211111(13)STEP8j=j+1STEP9gotostep5.Thewindowingcoefficients,w(|i-k|),arefoundinthetable1.SIST EN 300 969 V7.0.1:2003
ETSIETSIEN300969V7.0.1(2000-01)15(GSM06.20version7.0.1Release1998)Table1:Windowingcoefficientsw(0)0,998966w(5)0,974915w(1)0,996037w(6)0,969054w(2)0,991663w(7)0,963060w(3)0,986399w(8)0,956796w(4)0.980722w(9)0,950127Thisalgorithmcanbesimplifiedbynotingthattheφ',FandBmatricesaresymmetricsuchthatonlytheuppertriangularpartofthematricesneedtobecomputedorupdated.Also,step7isdonesothatFj(i,k),Bj(i-1,k-1),Cj(i,k-1),andCj(k,i-1)areupdatedtogetherandcommontermsarecomputedonceandtherecursionisdoneinplace.4.1.4SpectralquantizationAthreesegmentvectorquantizerofthereflectioncoefficientsisemployed.Areducedcomplexitysearchtechniqueisusedtoselectthevectorofreflectioncoefficientsforeachsegment.Thereflectioncoefficientvectorquantizercodebooksarestoredincompressedformtominimizetheirmemoryrequirements.Thethreesegmentsofthevectorquantizerspanreflectioncoefficientsr1r3,r4r6,andr7-r10respectively.Thebitallocationsforthevectorquantizersegmentsare:Q111bitsQ29bitsQ38bitsAreflectioncoefficientvectorprequantizerisusedateachsegment.Theprequantizersizeateachsegmentis:P16bitsP25bitsP34bitsAtagivensegment,theresidualerrorduetoeachvectorfromtheprequantizeriscomputedandstoredintemporarymemory.Thislistissearchedtoidentifythefourprequantizervectorswhichhavethelowestdistortion.Theindexofeachselectedprequantizervectorisusedtocalculateanoffsetintothevectorquantizertableatwhichthecontiguoussubsetofquantizervectorsassociatedwiththatprequantizervectorbegins.Thesizeofeachvectorquantizersubsetatthek-thsegmentisgivenby:SkQPkk=22(14)Thefoursubsetsofquantizervectors,associatedwiththeselectedprequantizervectors,aresearchedforthequantizervectorwhichyieldsthelowestresidualerror.Thusatthefirstsegment,64prequantizervectorsand128quantizervectorsareevaluated,32prequantizervectorsand64quantizervectorsareevaluatedatthesecondsegment,and16prequantizervectorsand64quantizervectorsareevaluatedatthethirdsegment.4.1.4.1AutocorrelationFixedPointLatticeTechnique(AFLAT)AnautocorrelationversionoftheFLATalgorithm,AFLAT,isusedtocomputetheresidualerrorenergyforareflectioncoefficientvectorbeingevaluated.ComputetheautocorrelationsequenceR(i),fromtheoptimalreflectioncoefficients,rj,overtherange0≤i≤Np.STEP1DefinetheinitialconditionsfortheAFLATrecursion:()()PiRiiNp001=≤≤−,(15)()()ViRiNiNpp0111=+−≤≤−,(16)SIST EN 300 969 V7.0.1:2003
ETSIETSIEN300969V7.0.1(2000-01)16(GSM06.20version7.0.1Release1998)STEP2Initializek,thevectorquantizersegmentindex:k=1(17)STEP3LetIl(k)betheindexofthefirstlatticestageinthek-thsegment,andIh(k)betheindexofthelastlatticestageinthek-thsegment.STEP4Initializej,theindexofthelatticestage,topointtothebeginningofthek-thsegment:()jIkl=(18)STEP5SettheinitialconditionsPj-1andVj-1to:()()()()PiPiiIkIkjjhl−−=≤≤−110,(19)()()()()()()ViViIkIkiIkIkjjihlhl−−=−+≤≤−1,(20)STEP6ComputethevaluesofVjandPjarraysusing:()()()()()[]()PirPirViViiIkjjjjjjjh=+++−≤≤−−−−−1012111,(21)()()()()ViVirVirPijNiNjjjijjijjpp=++−−+++−≤≤−−−−−11211121,(22)STEP7Incrementj:j=j+1STEP8Ifj
ETSIETSIEN300969V7.0.1(2000-01)17(GSM06.20version7.0.1Release1998)STEP14Ifj≤Ih(k)gotoSTEP12STEP15Incrementk,thevectorquantizersegmentindex:k=k+1STEP16Ifk≤3gotoSTEP4.Otherwise,theindicesofthereflectioncoefficientvectorsforthethreesegmentshavebeenchosen,andthesearchofthereflectioncoefficientvectorquantizeristerminated.Tominimizethestoragerequirementsforthereflectioncoefficientvectorquantizer,eightbitcodesfortheindividualreflectioncoefficientsarestoredinthevectorquantizertable,insteadoftheactualreflectioncoefficientvalues.Thecodesareusedtolookupthevaluesofthereflectioncoefficientsfromascalarquantizationtablewith256entries.4.1.5FrameenergycalculationandquantizationTheunquantizedvalueofR0,R(0),iscomputedduringthecomputationoftheshorttermpredictorparameters.()()()R01010320=+φφ0,0,(27)whereφ(i,k)isdefinedbyequation(5).R(0)isthenconvertedintodBrelativetofullscale(fullscale,Rmax,isdefinedasthesquareofthemaximumsampleamplitude).()RRRdB=10010logmax(28)RdBisthenquantizedto32levels.The32quantizedvaluesforRdBrangefromaminimumof-66(correspondingtoacodeof0forR0)toamaximumof-4(correspondingtoacodeof31forR0).Thestepsizeofthequantizeris2(2dBsteps).R0ischosenas:R0whichminimizesabs(R0-(RdB+66)/2)(29)whereR0cantakeontheintegervaluesfrom0to31correspondingtothe32codesforR0.DecodingoftheR0codeisgivenby:()()()RRR010206610=−max/(30)4.1.6SoftinterpolationofthespectralparametersInterpolationoftheshorttermfilterparametersimprovestheperformanceoftheGSMhalfrateencoder.Thedirectformfiltercoefficients(αi's),whichcorrespondtoquantizedreflectioncoefficients,arethespectralparametersusedforinterpolation.TheGSMhalfratespeechencoderuseseitheraninterpolatedsetofαi'soranuninterpolatedsetofαi's,choosingthesetwhichgivesbetterpredictiongainfortheframe.TwosetsofLPCcoefficientvectorsaregenerated:thefirstcorrespondstotheinterpolatedcoefficients,thesecondtotheuninterpolatedcoefficients.Theframe'sspeechsamplesareinversefilteredusingeachofthetwocoefficientsets,andtheresidualframeenergycorrespondingtoeachsetiscomputed.Thecoefficientsetyieldingthelowerframeresidualenergyisthenselectedtobeused.Iftheresidualenergiesareequal,theuninterpolatedcoefficientsetisused.INT_LPC,asoftinterpolationbit,issetto1wheninterpolationisselectedorto0otherwise.Togeneratetheinterpolatedcoefficientset,thecoderinterpolatestheαi'sforthefirst,second,andthirdsubframesofeachframe.Thefourthsubframeusestheuninterpolatedαi'sforthatframe.Theinterpolationisdoneasfollows.Letαi,Lbethedirect-formLPCcoefficientscorrespondingtothelastframe,αi,Cbethedirect-formLPCcoefficientscorrespondingtothecurrentframe,andDeltobetheinterpolationcurveused.Theinterpolateddirect-formLPCcoefficientvectoratthej-thsubframeofthecurrentframe,αi,j,isgivenby:SIST EN 300 969 V7.0.1:2003
ETSIETSIEN300969V7.0.1(2000-01)18(GSM06.20version7.0.1Release1998)ααααijiLiciLDeljINTSOFT,,,,(,_)()=+−,1≤i≤Np,1≤j≤4(31)ThevaluesoftheinterpolationcurveDelaregivenintable2.Table2:ValuesoftheinterpolationcurveDeljDel(j,0)Del(j,1)10,00,3021,00,6231,00,9241,01,00Fromthispointon,thesubframeindexjisomittedforsimplicitywhenreferringtoαi,jcoefficients,althoughitisimplied.Forinterpolatedsubframes,theαi'sareconvertedtoreflectioncoefficientstocheckforfilterstability.Iftheresultingfilterisunstable,thenuninterpolatedcoefficientsareusedforthatsubframe.Theuninterpolatedcoefficientsusedforsubframe1arethepreviousframe'scoefficients.Theuninterpolatedcoefficientsusedforsubframes2,3,and4arethecurrentframe'scoefficients.4.1.7SpectralnoiseweightingfiltercoefficientsToexploitthenoisemaskingpotentialoftheformants,spectralnoiseweightingisapplied.Thecomputationoftheαicoefficients,usedbyspectralnoiseweightingfiltersW(z)andH(z),isnowdescribed.Defineanimpulsesequenceδ(n)overNssamples:δ(),010=δ(),n=00(32)where1≤n≤Ns-1andh3(n)isthezero-stateresponseofthecascadeofthreefilterstoδ(n).ThethreefiltersareanLPCsynthesisfilter,aninversefilterusingaweightingfactorof0,93andasynthesisfilterwithaweightingfactorof0,7.Inequationform:hnnhniiiNp111()()()=+−=δα0≤n≤Ns-1(33)hnhnhniiiiNp2111093()()(,)()=−−=α0≤n≤Ns-1(34)hnhnhniiiNip321307()()(,)(),=+−=α0≤n≤Ns-1(35)whereαi'sarethedirectformLPcoefficients.Theautocorrelationsequenceofh3(n)iscalculatedusing:RihnhnihniNs3331()()(),=−=−0≤i≤Np(36)FromRih3()thereflectioncoefficientswhichdefinethecombinedspectrallynoiseweightedsynthesisfilterarecomputedusingtheAFLATrecursiononceperframe.SIST EN 300 969 V7.0.1:2003
ETSIETSIEN300969V7.0.1(2000-01)19(GSM06.20version7.0.1Release1998)STEP1DefinetheinitialconditionsfortheAFLATrecursion:PiRih03()(),=0≤i≤Np-1(37)()ViRih031(),=+1-Np≤i≤Np-1(38)STEP2Initializej,theindexofthelatticestage,topointtothefirstlatticestage:j=1STEP3Computerj,thej-threflectioncoefficient,using:rjVPjj=−−−1100()()(39)STEP4Givenrj,updatethevaluesofVjandPjarraysusing:()[]PirPirViVijjjjjj()()()()=+++−−−−12111,0≤i≤Np-j-1(40)()()ViVirVirPijjjjjj()(),=++−−++−−−121111211+j-Np≤i≤Np-j-1(41)STEP5Incrementj:j=j+1STEP6Ifj≤NpgotoSTEP3,otherwiseallNpreflectioncoefficientshavebeenobtained.STEP7Thereflectioncoefficients,rj,arethenconvertedtodirect-formLPCfiltercoefficients,αiforimplementingthecombinedspectrallynoiseweightedsynthesisfilterH(z)andthefilterW(z).ThemethodforthespectralnoiseweightingfiltercoefficientupdatemimickshowthedirectformLPCfiltercoefficientsareupdatedatsubframesofaframe(subclause4.1.6).Nostabilitycheckofinterpolatedspectralnoiseweightingfiltercoefficientsisdoneatsubframes1,2,or3iftheinterpolationflag,INT_LPC="1",butifuninterpolatedcoefficientsareusedatsubframes1,2,and/or3duetoinstabilityoftheunweightedcoefficients(INT_LPC="0"),uninterpolatedweightingfiltercoefficientsarealsousedatthosesubframes.4.1.8LongTermPredictorlagdeterminationFigure3illustratesthatthelongtermlagoptimizationlooksjustlikeacodebooksearchwherethecodebookisdefinedbythelongtermfilterstateandthespecificvectorinthecodebookispointedtobythelongtermpredictorlag,L.Theinputp(n)istheweightedinputspeechforthesubframeminusthezeroinputresponseofjusttheH(z)filter.Σ( )2X-Lββββb(n)Lp'(n)p(n)e(n)totalweightederrorLongtermfilterstateH(z)Figure3:LongtermpredictorlagsearchTheGSMhalfratespeechencoderusesacombinationofopenloopandclosedlooptechniquesinchoosingthelongtermpredictorlag.Firstanopenloopsearchisconductedtodetermine"candidate"lagsateachsubframe.Thenatmost,twobestcandidatelagsateachsubframeareselected,witheachservingasananchorpointforconstructinganopenloopframelagtrajectory,subjecttoamaximumdeltacodingconstraint.TheframelagtrajectorywhichminimizestheSIST EN 300 969 V7.0.1:2003
ETSIETSIEN300969V7.0.1(2000-01)20(GSM06.20version7.0.1Release1998)openloopLTPspectrallyweightederrorenergyfortheframeisthenchosen.TheopenloopLTPpredictiongainscorrespondingtothewinningtrajectoryareusedtoselectthevoicingmode1,2or3.IfMODE≠0,theclosedlooplagevaluationisinitiated.Thewinningtrajectoryhasassociatedwithitalistoflagstobesearchedclosedloopateachsubframe.ItispossibletoallowLtotakeonfractionalvalues,thusincreasingtheresolution,andinturntheperformance,oftheadaptivecodebook.Table3showstheallowablelags.Table3:AllowablelagsRangeResolutionNumberoflagsinrange21to222/31/3623to345/61/67235to492/31/34550to891/21/28090to142153Theresolutionofthelongtermfilterstatemaybeincreasedbyupsamplingandfilteringthestate.Inthisimplementation,anon-causal,zero-phaseFiniteImpulseResponse(FIR)filterisused.Whereneeded,thefuturesamplesforthenon-causalfilteringoperationarereplacedbytheoutputofthepredictor.4.1.8.1OpenlooplongtermsearchinitializationAnopen-looplagsearchisdonetonarrowtherangeoflagsoverwhichaclosed-loopsearchwilleventuallybeperformed.Thefirststepsoftheopen-loopsubframelagsearchareasfollows:STEP1Initializethesubframecounterm=1STEP2Theautocorrelationsequenceofy(n)theinputspeech,s(n),filteredbyW,iscalculatedforallallowableintegerlags,andforafewintegerlagsbelowandabovethelowerandupperlimitsforthecurrentsubframe.()()()()CkmynmNynmNksnNss(,),=+−+−−=−1101LPkLPggminmax−≤≤+−221(42)whereLmin=21andLmax=142.ThevaluePgistheorderofonephaseoftheinterpolatingFIRfilterusedtointerpolatethecorrelations.Theenergyofy(n)forthesubframeiscomputed:()()GkmynmNksnNs(,),=+−−=−2011LPkLPggminmax−≤≤+−221(43)STEP3Thesearrays,C(k,m)andG(k,m),aresearchedfortheintegerlagwhichmaximizesC2(k,m)/G(k,m)whereC(k,m)andG(k,m)needtobegreaterthan0.STEP4Ifavalidmaximumisfoundinstep3,thevaluesforthelag,C,andGcorrespondingtothemaximumareretainedinthearraysasLpeak(0,m),Cpeak(0,m),andGpeak(0,m).Otherwise,Lpeak(0,m)=Lmin(44)Cpeak(0,m)=0(45)Gpeak(0,m)=1(46)STEP5m=m+1SIST EN 300 969 V7.0.1:2003
ETSIETSIEN300969V7.0.1(2000-01)21(GSM06.20version7.0.1Release1998)STEP6Ifm≤4,gotostep2STEP7CalculatetheopenloopframeLTPpredictiongain:PRmRmCmGmvmpeakpeakm=−==1000001014214log(,)(,)(,)(,)(47)where()()RmynmNssnN(,)01201=+−=−,(48)STEP8Determineifthevoicingmodeisunvoiced:IfPv<1,7thenMODE=0,thelongtermpredictorisdisabledandtheopenloopandclosedlooplagsearchesareaborted.Inthiscase,proceedtosubclause4.1.10.4.1.8.2OpenlooplagsearchWhenMODE≠0,thelagsearchprocessingiscontinued.Thenextpartofthesearchfindstheallowablelag(seetable3)whichmaximizesCG2inthevicinityofthebestopen-loopintegerresolutionlag,Lpeak(0,m),forvaluesofC>0.STEP1Initializethesubframecounterm=1STEP2InitializethepeakindexLp,m=0STEP3UsinginterpolatedversionsoftheCandGarrays,allowablelagvaluesk'intherange:Lpeak(0,m)-1
ETSIETSIEN300969V7.0.1(2000-01)22(GSM06.20version7.0.1Release1998)()CkgiCkimIji()(),=−+=305(51)()GkgiGkimIji()(),=−+=305(52)and()jkk=−6(53)Thecoefficientsoftheinterpolatingfilteraregj(i)for0≤i≤5.OnlyCI(k)>0andGI(k)>0valuesareconsidered.Ifnopositivecorrelationisfound,thensetλhnw,m=0,Lpeak(1,m)=Lmin,andgotoStep22.Otherwise,storetheinformationrelatedtothevalidbestallowablelagk.Lp,m=Lp,m+1(54)Lpeak(Lp,m,m)=k(55)Cpeak(Lp,m,m)=CI(k)(56)Gpeak(Lp,m,m)=GI(k)(57)ThenextpartofthesearchevaluatesCG2,forC>0andG>0,atthesubmultiplesofthelagLpeak(Lp,m,m)tofindcandidatepeaks.STEP4InitializethedivisorJ=2STEP5Findnearestintegerlagcorrespondingtosubmultipleofmaximumpeakk1=round[Lpeak(1,m)/J](58)STEP6DetermineifsubmultipleiswithinallowablelagrangeIfk1
ETSIETSIEN300969V7.0.1(2000-01)23(GSM06.20version7.0.1Release1998)STEP8Determineifmaximuminstep7isapeakIf()()()()CkmGkmCkmGkm2211',',',',−−>(60)Gotostep11If()()()()CkmGkmCkmGkm2211',',',',++>(61)Gotostep11STEP9Apeakhasbeenfoundatanintegerlag,k'.UsinginterpolatedversionsoftheCandGarrays,allowablelagvalueswithin+1(exclusive)ofk'aresearched.FindkwhereCkGkII2()()(62)isamaximum,where()CkgiCkimIji()(),=−+=305(63)()GkgiGkimIji()(),=−+=305(64)where()jkk=−6(65)andk'-10andGI(k)>0areconsidered.STEP10Ifthepredictiongainexceedsathreshold,thecorrespondinglag,CI,andGIarestoredintheLpeak(),Cpeak(),andGpeak()arrays;othe
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