Editing Harmonic Vector Excitation Coding (section)

{{short description|Audio compression standard}}
'''Harmonic Vector Excitation Coding''', abbreviated as '''HVXC''' is a [[speech coding]] [[algorithm]] specified in [[MPEG-4 Part 3]] (MPEG-4 Audio) standard for very low [[bit rate]] speech coding. HVXC supports bit rates of 2 and 4&nbsp;kbit/s in the fixed and [[variable bit rate]] mode and [[sampling frequency]] of 8&nbsp;kHz. It also operates at lower bitrates, such as 1.2 - 1.7&nbsp;kbit/s, using a variable bit rate technique.<ref name="mpeg4audio-version4-2009">{{Citation | url=http://webstore.iec.ch/preview/info_isoiec14496-3%7Bed4.0%7Den.pdf | title=ISO/IEC 14496-3:2009 - Information technology -- Coding of audio-visual objects -- Part 3: Audio | format=PDF | author=[[International Organization for Standardization|ISO]]/[[International Electrotechnical Commission|IEC]] | publisher=IEC | date=2009-09-01 | access-date=2009-10-07}}</ref> The total algorithmic [[Latency (audio)|delay]] for the encoder and decoder is 36 ms.<ref name="hvxc">{{Citation | url=http://www.jstage.jst.go.jp/article/ast/27/6/27_6_375/_pdf | title=Harmonic vector excitation coding of speech | author=Masayuki Nishiguchi | publisher=Acoustical Science and Technology | format=PDF | date=2006-04-17 | access-date=2009-10-09}}</ref>

It was published as subpart 2 of [[International Organization for Standardization|ISO]]/[[International Electrotechnical Commission|IEC]] 14496-3:1999 (MPEG-4 Audio) in 1999.<ref name="mpeg4audio">{{Cite web | url=http://www.iso.org/iso/iso_catalogue/catalogue_ics/catalogue_detail_ics.htm?csnumber=25035 | title=ISO/IEC 14496-3:1999 - Information technology -- Coding of audio-visual objects -- Part 3: Audio | author=[[International Organization for Standardization|ISO]] | publisher=ISO | year=1999 | access-date=2009-10-09}}</ref> An extended version of HVXC was published in MPEG-4 Audio Version 2 (ISO/IEC 14496-3:1999/Amd 1:2000).<ref name="mpeg4audio-iso-2-amd">{{Cite web | url=http://www.iso.org/iso/iso_catalogue/catalogue_ics/catalogue_detail_ics.htm?csnumber=31568 | title=ISO/IEC 14496-3:1999/Amd 1:2000 - Audio extensions | author=[[International Organization for Standardization|ISO]] | publisher=ISO | year=2000 | access-date=2009-10-07}}</ref><ref name="mpeg4audio-version2">{{Cite FTP | url=ftp://ftp.tnt.uni-hannover.de/pub/MPEG/audio/mpeg4/documents/w2803/w2803_n.pdf | title=ISO/IEC 14496-3:/Amd.1 - Final Committee Draft - MPEG-4 Audio Version 2 | format=PDF | author=[[International Organization for Standardization|ISO]]/[[International Electrotechnical Commission|IEC]] JTC 1/SC 29/WG 11 | date=July 1999 | access-date=2009-10-07 | url-status=dead | server=FTP server }}</ref>

MPEG-4 Natural Speech Coding Tool Set uses two algorithms: HVXC and CELP ([[Code Excited Linear Prediction]]). HVXC is used at a low bit rate of 2 or 4 kbit/s. Higher bitrates than 4 kbit/s in addition to 3.85 kbit/s are covered by CELP.<ref name="speech-coding-chiariglione">{{Cite web | url=http://www.mp3-tech.org/programmer/docs/audio.pdf| title=MPEG-4 Natural Audio Coding - Natural Speech Coding Tools |author1=Karlheinz Brandenburg |author2=Oliver Kunz |author3=Akihiko Sugiyama | access-date=2013-03-25}}</ref>