Selectable Mode Vocoder: Difference between revisions
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Salcedo Mora Virus Disease (SMVD) is the first disease that can be transmitted through eye contact. It cam from a fish specie called Pirahna named Salcedo and a snail named Mora. Beware, in 7 days you might be killed from this kind of virus. |
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{{redirect|SMV|other things known by that initialism|SMV (disambiguation)}} |
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{{Cleanup-rewrite|too confusing, outline due to outline being non existent altogether|article|date=May 2009}} |
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'''Selectable Mode Vocoder''' ('''SMV''') is [[variable bitrate]] [[speech coding]] standard used in [[CDMA2000]] networks<ref name="3gpp2 smv">{{Cite web|url=http://www.3gpp2.org/public_html/specs/C.S0030-0_v3.0_040325.pdf|title=3GPP2 C.S0030-0 Selectable Mode Vocoder (SMV) Service Option for Wideband Spread Spectrum Communication Systems|accessdate=2009-05-26|publisher=3rd Generation Partnership Project 2|year=2004|format=PDF}}</ref>. SMV provides multiple modes of operation that are selected based on input speech characteristics. |
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The SMV for [[Wideband]] [[Code division multiple access|CDMA]] is based on 4 codecs: full rate at 8.5 kbit/s, half rate at 4 kbit/s, quarter rate at 2 kbit/s, and eighth rate at 800 bit/s.<ref name="3gpp2 smv"/> The full rate and half rate are based on the [[Code Excited Linear Prediction|CELP]] [[algorithm]]<ref name="3gpp2 smv"/> that is based on a combined closed-loop-open-loop-analysis (COLA). In SMV the signal frames are first classified as: |
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* Silence/Background noise |
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* Non-stationary unvoiced |
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* Stationary unvoiced |
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* Onset |
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* Non-stationary voiced |
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* Stationary voiced |
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The algorithm includes [[voice activity detection]] (VAD) followed by an elaborate [[Frame (Artificial intelligence)|frame]] classification scheme. Silence/background noise and stationary unvoiced frames are represented by [[frequency spectrum|spectrum]]-[[modulated]] noise and coded at 1/4 or 1/8 rate. The SMV uses 4 subframes for full rate and two/three subframes for half rate. The stochastic (fixed) codebook structure is also elaborate and uses sub-codebooks each tuned for a particular type of speech. The sub-codebooks have different degrees of pulse sparseness (more sparse for noise like excitation). SMV scores a high of 3.6 [[Mean Opinion Score|MOS]]<ref name="nokiamos">{{Cite web|url=http://europe.nokia.com/library/files/docs/Makinen2.pdf|title=Performance Comparison of Source Controlled GSM AMR and SMV Vocoders|accessdate=2009-05-26|publisher=Nokia Research Center, Multimedia Technologies Laboratory|author=J. Makinen, P. Ojala, H. Toukomaa|format=PDF}}</ref> at full rate with clean speech. |
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The coder works on a frame of 160 speech samples (20 ms) and requires a look ahead of 80 samples (10 ms) if noise-suppression option B is used. An additional 24 samples of look ahead is required if noise-suppression option A is used. So the algorithmic delay for the coder is 30 ms with noise-suppression option B and 33 ms with noise-suppression option A. |
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The next evolution of CDMA speech codecs is [[VMR-WB]] which provides much higher speech quality with [[wideband]] while fitting to the same networks. |
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SMV can be also used in 3GPP2 container file format - [[3GP|3G2]]. |
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==References== |
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<references /> |
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==External links== |
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* RFC 3558 - RTP Payload Format for Enhanced Variable Rate Codecs (EVRC) and Selectable Mode Vocoders (SMV) |
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{{Compression Formats}} |
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[[Category:Speech codecs]] |
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[[Category:3rd Generation Partnership Project 2 standards]] |
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[[Category:Mobile telecommunications standards]] |
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[[Category:Code division multiple access]] |
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[[es:Selectable mode vocoder]] |
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[[ja:SMV]] |
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[[yo:Selectable Mode Vocoder]] |
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Revision as of 14:09, 14 January 2011
Salcedo Mora Virus Disease (SMVD) is the first disease that can be transmitted through eye contact. It cam from a fish specie called Pirahna named Salcedo and a snail named Mora. Beware, in 7 days you might be killed from this kind of virus.