{{Short description|Audio codec}} '''Siren''' is a family of patented, transform-based, wideband audio coding formats and their audio codec implementations developed and licensed by PictureTel Corporation (acquired by Polycom, Inc. in 2001).<ref name="picturetel">{{cite web |author=Business Wire |publisher=thefreelibrary.com |url=http://www.thefreelibrary.com/PictureTel+Announces+New+Siren+Wideband+Audio+Technology+Licensing...-a072261882 |title=PictureTel Announces New Siren Wideband Audio Technology Licensing Program |date=2001-03-26 |access-date=2009-09-10 |archive-date=2012-10-13 |archive-url=https://web.archive.org/web/20121013184749/http://www.thefreelibrary.com/PictureTel+Announces+New+Siren+Wideband+Audio+Technology+Licensing...-a072261882 |url-status=dead }}</ref> There are three Siren codecs: Siren 7, Siren 14 and Siren 22.

== Editions == '''Siren 7''' (or Siren7 or simply Siren) provides 7&nbsp;kHz audio, bit rates 16, 24, 32&nbsp;kbit/s and sampling frequency 16&nbsp;kHz. Siren is derived from PictureTel's PT716plus algorithm.<ref name="picturetel-intel">{{cite web |author=Business Wire |publisher=thefreelibrary.com |url=http://www.thefreelibrary.com/PictureTel+Licenses+Audio+Technology+Suite+to+Intel.-a063558475 |title=PictureTel Licenses Audio Technology Suite to Intel |date=2000-07-19 |access-date=2009-09-10 |archive-date=2012-10-13 |archive-url=https://web.archive.org/web/20121013184755/http://www.thefreelibrary.com/PictureTel+Licenses+Audio+Technology+Suite+to+Intel.-a063558475 |url-status=dead }}</ref> In 1999, ITU-T approved G.722.1 recommendation, which is based on Siren 7 algorithm. It was approved after a four-year selection process involving extensive testing.<ref name="picturetel-intel" /> G.722.1 provides only bit rates 24 and 32&nbsp;kbit/s and does not support Siren 7's bit rate 16&nbsp;kbit/s.<ref>(2008-08-05) [https://www.reuters.com/article/pressRelease/idUS135735+05-Aug-2008+MW20080805 Polycom Enables Acceleration of HD Voice Adoption by Offering Royalty-Free Codec] {{Webarchive|url=https://archive.today/20130201102055/http://www.reuters.com/article/pressRelease/idUS135735+05-Aug-2008+MW20080805 |date=2013-02-01 }}, Retrieved 2009-09-07</ref><ref name="g7221-faq">{{cite web |publisher=Polycom, Inc. |url=http://www.polycom.com/company/about_us/technology/siren_g7221/faq.html |title=Polycom Siren/G 722.1 FAQs |access-date=2009-09-07}}</ref> The algorithm of Siren 7 is identical to its successor, G.722.1, although the data formats are slightly different.

'''Siren 14''' (or Siren14) provides 14&nbsp;kHz audio, bit rates 24, 32, 48&nbsp;kbit/s for mono, 48, 64, 96&nbsp;kbit/s for stereo and sampling frequency 32&nbsp;kHz. Siren 14 supports stereo and mono audio. It offers 40 millisecond algorithmic delay, using 20 millisecond frame lengths. The mono version of Siren 14 became ITU-T G.722.1C (14&nbsp;kHz, 24/32/48&nbsp;kbit/s) in April 2005.<ref name="g7221c">Polycom, Inc. (2005-04-12) [http://findarticles.com/p/articles/mi_m0EIN/is_2005_April_12/ai_n13600182/ ITU Approves Polycom Siren14 as New International Standard], Retrieved 2009-09-07</ref><ref name="g7221c-polycom">{{cite web |publisher=Polycom, Inc. |url=http://www.polycom.com/company/about_us/technology/siren14_g7221c/index.html |title=Polycom Siren 14/G 722.1C |access-date=2009-09-07}}</ref><ref name="businesswire">{{cite web |publisher=BusinessWire.com |url=http://www.businesswire.com/portal/site/home/permalink/?ndmViewId=news_view&newsId=20050412005325&newsLang=en |title=ITU Approves Polycom Siren14 as New International Standard |date=2005-04-12 |access-date=2009-09-10}}</ref> The algorithm is based on transform coding technology, using a modulated lapped transform (MLT),<ref>{{citation |url=http://www.polycom.com/global/documents/company/about_us/technology/siren14_g7221c/info_for_prospective_licensees.pdf |title=Siren 14 information for Prospective Licensees |access-date=2010-06-08}}</ref> a type of discrete cosine transform (DCT)<ref>{{cite book |last1=Hersent |first1=Olivier |last2=Petit |first2=Jean-Pierre |last3=Gurle |first3=David |title=Beyond VoIP Protocols: Understanding Voice Technology and Networking Techniques for IP Telephony |date=2005 |publisher=John Wiley & Sons |isbn=9780470023631 |page=55 |url=https://books.google.com/books?id=SMvNToRs-DgC&pg=PA55}}</ref> or modified discrete cosine transform (MDCT).<ref>{{cite book |last1=Britanak |first1=Vladimir |last2=Rao |first2=K. R. |author2-link=K. R. Rao |title=Cosine-/Sine-Modulated Filter Banks: General Properties, Fast Algorithms and Integer Approximations |date=2017 |publisher=Springer |isbn=9783319610801 |page=478 |url=https://books.google.com/books?id=cZ4vDwAAQBAJ&pg=PA478}}</ref>

'''Siren 22''' (or Siren22) provides 22&nbsp;kHz audio, sampling frequency 48&nbsp;kHz, bit rates 64, 96, 128&nbsp;kbit/s stereo and 32, 48, 64&nbsp;kbit/s mono. Siren 22 offers 40 millisecond algorithmic delay using 20 millisecond frame lengths. In May 2008, ITU-T approved the new G.719 full-band codec which is based on Polycom Siren 22 audio technology and Ericsson's advanced audio techniques.<ref name="siren22-polycom">{{cite web |publisher=Polycom, Inc. |url=http://www.polycom.com/company/about_us/technology/siren22/index.html |title=Polycom Siren 22 |access-date=2009-09-07}}</ref><ref name="g719-polycom">{{cite web |publisher=Polycom, Inc. |url=http://www.polycom.com/global/documents/whitepapers/g719-the-first-itut-standard-for-full-band-audio.pdf |title=G.719: The First ITU-T Standard for Full-Band Audio |date=April 2009 |access-date=2009-09-07}}</ref>

== Software support == Siren 7 is commonly used in videoconferencing systems and is also part of Microsoft Office Communicator when using A/V conferencing. Microsoft Office Communications Server uses Siren 7 during audio conferencing. With the default Office Communicator client, point to point audio is by default performed using Microsoft's proprietary codec RTAudio. When a call is promoted into an audio conference (any time 3 or more participants have joined), the codec is switched on the fly to Siren. This is done for performance reasons. Note that even if the conference is reduced to below 3 participants, OCS does not demote the conference to be point-to-point; it remains an A/V conference until the conference is terminated.

In Windows XP and later versions of Windows, the Siren 7 codec is implemented in {{mono|%systemroot%\system32\SIRENACM.DLL}}. It is used by MSN Messenger and Live Messenger for sending and receiving voice clips and also as one of the available codecs for the 'Computer Call' feature.<ref name="multimediawiki">{{cite web |publisher=MultimediaWiki |url=http://wiki.multimedia.cx/index.php?title=Siren |title=Siren |access-date=2009-09-07}}</ref><ref name="mplayer">{{cite web |publisher=MultimediaWiki |url=http://www.mplayerhq.hu/DOCS/codecs-status.html#ac |title=MPlayer - Status of codecs support |access-date=2009-09-07}}</ref><ref name="winxp">{{cite web |author=Microsoft |publisher=Microsoft |url=http://msdn.microsoft.com/en-us/library/ms997607.aspx |title=Media Support in the Microsoft Windows Real-Time Communications Platform |date=November 2001 |access-date=2009-09-07}}</ref>

FreeSWITCH communication open source software can do transcoding, conferencing and bridging of Siren 7/G.722.1 and Siren 14/G.722.1C audio formats.<ref name="freeswitch">{{cite web |publisher=FreeSWITCH |url=http://www.freeswitch.org/node/153 |title=FreeSWITCH First to Support Polycom's 32khz HD-Audio. |date=2008-12-15 |access-date=2009-09-07 |archive-url=https://web.archive.org/web/20090508170812/http://freeswitch.org/node/153 |archive-date=2009-05-08 |url-status=dead }}</ref><ref name="libg7221">{{cite web |publisher=FreeSWITCH |url=https://stash.freeswitch.org/projects/FS/repos/freeswitch/browse/libs/libg722_1/COPYING |title=libg722_1 - COPYING |access-date=2014-07-19}}</ref><ref name="libg7221-readme">{{cite web |publisher=FreeSWITCH |url=https://stash.freeswitch.org/projects/FS/repos/freeswitch/browse/libs/libg722_1/README |title=libg722_1 - README |access-date=2014-07-19}}</ref>

aMSN, an open source Windows Live Messenger clone uses for Siren audio compression and decompression the "libsiren" library, an open source implementation of the codec, written by aMSN developer Youness Alaoui (KaKaRoTo) .<ref name="kakaroto">KaKaRoTo (2008-02-12) [http://pidgin.im/pipermail/openim/2008-February/000045.html MSN Protocol documentation] {{Webarchive|url=https://web.archive.org/web/20130524081438/http://pidgin.im/pipermail/openim/2008-February/000045.html |date=2013-05-24 }}, Pidgin.im mailinglist, Retrieved 2009-09-08</ref> The libsiren library has also been copied into libmsn and into the msn-pecan project, which provides plug-in for Pidgin and Adium instant messaging clients.<ref name="kakaroto" /><ref name="msn-pecan0018">{{cite web |publisher=msn-pecan |url=http://felipec.wordpress.com/2009/02/16/msn-pecan-0018-released-now-with-voice-clips-support/ |title=msn-pecan 0.0.18 released, now with voice clips support |date=2009-02-16 |access-date=2014-07-19}}</ref><ref name="msn-pecan">{{cite web |publisher=msn-pecan |url=http://code.google.com/p/msn-pecan/ |title=msn-pecan |access-date=2009-09-07}}</ref><ref name="libmsn">{{cite web |publisher=Libmsn project at Sourceforge.net |url=https://sourceforge.net/projects/libmsn/ |title=Libmsn - is a reusable, open-source, fully documented library for connecting to Microsoft's MSN Messenger service. |year=2009 |access-date=2009-09-07}}</ref><ref name="libmsn-svn">{{cite web |publisher=Libmsn project at Sourceforge.net |url=https://libmsn.svn.sourceforge.net/viewvc/libmsn/trunk/msn/libsiren/ |title=SCM Repositories - libmsn - libsiren |year=2009 |access-date=2009-09-07}}</ref>

==Licensing==

Usage of Siren 7 and Siren 14 audio coding formats require the licensing of patents from Polycom, in most countries. A royalty free licence for Siren 7 and Siren 14 is available from Polycom if certain fairly basic conditions are met.<ref name="g7221-faq" /><ref name="libg7221" /><ref name="celt-comparison">{{cite web |author=Xiph.Org Foundation |publisher=Xiph.Org Foundation |url=http://www.celt-codec.org/comparison/ |title=CELT - Codec Feature Comparison |year=2009 |access-date=2009-09-07 |archive-date=2009-09-12 |archive-url=https://web.archive.org/web/20090912184544/http://www.celt-codec.org/comparison/ |url-status=dead }}</ref><ref name="speex-comparison">{{cite web |author=Xiph.Org Foundation |publisher=Xiph.Org Foundation |url=http://www.speex.org/comparison/ |title=Speex - Codec Quality Comparison |year=2006 |access-date=2009-09-07}}</ref><ref name="licensing">{{cite web |publisher=Polycom, Inc. |url=http://www.polycom.com/company/about_us/technology/siren_g7221/license_schedule.html |title=Siren7/Siren14/G.719 License info |access-date=2009-09-07}}</ref><ref name="g7221c-licensing">{{cite web |publisher=Polycom, Inc. |url=http://www.polycom.com/company/about_us/technology/siren14_g7221c/faq.html#license_q3 |title=Polycom Siren 14/G 722.1C FAQs - What are the terms on the free license? |access-date=2009-09-07}}</ref><ref name="polycom-free-hd-voice">{{cite web |author=Greg Galitzine |publisher=TMCnet.com |url=http://technews.tmcnet.com/reseller/topics/wideband-audio/articles/36272-polycom-cto-discusses-siren-7-hd-voice-codec.htm |title=Polycom CTO Discusses Siren 7 HD Voice Codec |date=2008-08-06 |access-date=2014-07-19}}</ref>

Usage of Siren 22 also requires the licensing of patents from Polycom.<ref name="licensing" />

==See also== * Comparison of audio coding formats * G.722.1

==References== {{reflist}}

==External links== * [http://www.polycom.com/company/about_us/technology/siren_g7221/ Polycom Siren/G 722.1] * [http://www.polycom.com/company/about_us/technology/siren_g7221/faq.html Polycom Siren/G 722.1 FAQs] * [http://www.polycom.com/company/about_us/technology/siren14_g7221c/index.html Polycom Siren 14/G 722.1C] * [http://www.polycom.com/company/about_us/technology/siren22/index.html Polycom Siren 22]

{{Compression formats}}

Category:Audio codecs