Siren is a family of patented, transform-based,

wideband In communications, a system is wideband when the message bandwidth significantly exceeds the coherence bandwidth of the channel. Some communication links have such a high data rate that they are forced to use a wide bandwidth; other links ma ...

audio coding formats An audio coding format (or sometimes audio compression format) is a content representation format for storage or transmission of digital audio (such as in digital television, digital radio and in audio and video files). Examples of audio coding f ...

and their

audio codec An audio codec is a device or computer program capable of encoding or decoding a digital data stream (a codec) that encodes or decodes audio. In software, an audio codec is a computer program implementing an algorithm that compresses and decompres ...

implementations developed and licensed by PictureTel Corporation (acquired by

Polycom Poly, formerly Polycom, a part of HP Inc., is an American multinational corporation that develops video, voice and content collaboration and communication technology. Polycom was co-founded in 1990 by Brian L Hinman and Jeffrey Rodman. In 2018 ...

, Inc. in 2001). There are three Siren codecs: Siren 7, Siren 14 and Siren 22.

Editions

Siren 7 (or Siren7 or simply Siren) provides 7 kHz audio,

bit rate In telecommunications and computing, bit rate (bitrate or as a variable ''R'') is the number of bits that are conveyed or processed per unit of time. The bit rate is expressed in the unit bit per second (symbol: bit/s), often in conjunction ...

s 16, 24, 32 kbit/s and

sampling frequency In signal processing, sampling is the reduction of a continuous-time signal to a discrete-time signal. A common example is the conversion of a sound wave to a sequence of "samples". A sample is a value of the signal at a point in time and/or s ...

16 kHz. Siren is derived from PictureTel's PT716plus algorithm. In 1999,

ITU-T The ITU Telecommunication Standardization Sector (ITU-T) is one of the three sectors (divisions or units) of the International Telecommunication Union (ITU). It is responsible for coordinating standards for telecommunications and Information Co ...

approved G.722.1 recommendation, which is based on Siren 7 algorithm. It was approved after a four-year selection process involving extensive testing. G.722.1 provides only bit rates 24 and 32 kbit/s and does not support Siren 7's bit rate 16 kbit/s. 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 kHz audio, bit rates 24, 32, 48 kbit/s for mono, 48, 64, 96 kbit/s for stereo and sampling frequency 32 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 kHz, 24/32/48 kbit/s) in April 2005.Polycom, Inc. (2005-04-12
ITU Approves Polycom Siren14 as New International Standard
Retrieved 2009-09-07 The algorithm is based on

transform coding Transform coding is a type of data compression for "natural" data like audio signals or photographic images. The transformation is typically lossless (perfectly reversible) on its own but is used to enable better (more targeted) quantization, ...

technology, using a modulated lapped transform (MLT), a type of discrete cosine transform (DCT) or

modified discrete cosine transform The modified discrete cosine transform (MDCT) is a transform based on the type-IV discrete cosine transform (DCT-IV), with the additional property of being lapped: it is designed to be performed on consecutive blocks of a larger dataset, where ...

(MDCT). Siren 22 (or Siren22) provides 22 kHz audio, sampling frequency 48 kHz, bit rates 64, 96, 128 kbit/s stereo and 32, 48, 64 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 G.719 is an ITU-T standard audio coding format providing high quality, moderate bit rate (32 to 128 kbit/s) wideband (20 Hz - 20 kHz audio bandwidth, 48 kHz audio sample rate) audio coding at low computational load. It was produced th ...

full-band codec which is based on Polycom Siren 22 audio technology and Ericsson's advanced audio techniques.

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 Skype for Business Server (formerly Microsoft Office Communications Server and Microsoft Lync Server) is real-time communications server software that provides the infrastructure for enterprise instant messaging, presence, VoIP, ad hoc and st ...

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 RTAudio is a Microsoft produced adaptive wide-band speech codec. It is used by Microsoft Office Communications Server (OCS) and the related OCS clients ( Microsoft Office Communicator, and Microsoft Live Meeting Console). RTAudio was designed for ...

. 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 . 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.

FreeSWITCH FreeSWITCH is free and open-source server software for real-time communication applications, including WebRTC, video, and voice over Internet Protocol (VoIP). It runs on Linux, Windows, macOS, and FreeBSD. FreeSWITCH is used to build private bran ...

communication open source software can do transcoding, conferencing and bridging of Siren 7/G.722.1 and Siren 14/G.722.1C audio formats.

aMSN aMSN is a free Windows Live Messenger clone. aMSN attempts to emulate the look and feel of Windows Live Messenger, and supports many of its features. It has been downloaded approximately 40 million times as of January 2011, making it the 21st mo ...

, 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) .KaKaRoTo (2008-02-12
MSN Protocol documentation
, Pidgin.im mailinglist, Retrieved 2009-09-08 The libsiren library has also been copied into libmsn and into the msn-pecan project, which provides plug-in for

Pidgin A pidgin , or pidgin language, is a grammatically simplified means of communication that develops between two or more groups of people that do not have a language in common: typically, its vocabulary and grammar are limited and often drawn from s ...

and Adium instant messaging clients.

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. Usage of Siren 22 also requires the licensing of patents from Polycom.

References

External links

Polycom Siren/G 722.1

{{Compression formats Audio codecs

Editions

Software support

Licensing

See also

References

External links