| dbo:abstract |
Selectable mode vocoder o SMV es un estándar de codificación de voz de tasa de bits variable, usado en redes CDMA2000. SMV usa distintos modos de operación que son seleccionanos sobre la base de las características de la voz usada como entrada. Constituyen una de las versiones de codificadores de voz en radiotelefonía. SMV es un codificador de voz que entrega una buena calidad de codificación y una mejora en la capacidad de tratar el ruido de fondo, característica muy solicitada en la próxima generación de diseños radio. Además, el funcionamiento multimodo ofrece mayor eficiencia del ancho de banda, tanto en medios radioeléctricos como de cable, permitiendo a los diversos operadores de red aumentar el número de conexiones simultáneas de voz en un mismo canal. (es) Selectable Mode Vocoder (SMV) is variable bitrate speech coding standard used in CDMA2000 networks. SMV provides multiple modes of operation that are selected based on input speech characteristics. The SMV for Wideband 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. The full rate and half rate are based on the CELP algorithm that is based on a combined closed-loop-open-loop-analysis (COLA). In SMV the signal frames are first classified as: * Silence/Background noise * Non-stationary unvoiced * Stationary unvoiced * Onset * Non-stationary voiced * Stationary voiced The algorithm includes voice activity detection (VAD) followed by an elaborate frame classification scheme. Silence/background noise and stationary unvoiced frames are represented by 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 MOS at full rate with clean speech. 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. The next evolution of CDMA speech codecs is VMR-WB which provides much higher speech quality with wideband while fitting to the same networks. SMV can be also used in 3GPP2 container file format – 3G2. (en) SMV（selectable mode vocoder）は CDMA2000 ネットワークで利用される可変ビットレートの音声符号化方式である。それ以前から CDMA ネットワークで使われている符号化方式の EVRC のように通話中に音声の内容によりビットレートを変えることができることに加え、モード指定により基地局側から音質と平均ビットレートの制御を行うことができる特徴がある。 この特徴はその後に規格化された CDMA2000 ネットワーク用の音声符号化方式である VMR-WB や EVRC-B 以降の仕様などにも引き継がれている。 (ja) |
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dbr:Speech |
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| rdfs:comment |
SMV（selectable mode vocoder）は CDMA2000 ネットワークで利用される可変ビットレートの音声符号化方式である。それ以前から CDMA ネットワークで使われている符号化方式の EVRC のように通話中に音声の内容によりビットレートを変えることができることに加え、モード指定により基地局側から音質と平均ビットレートの制御を行うことができる特徴がある。 この特徴はその後に規格化された CDMA2000 ネットワーク用の音声符号化方式である VMR-WB や EVRC-B 以降の仕様などにも引き継がれている。 (ja) Selectable mode vocoder o SMV es un estándar de codificación de voz de tasa de bits variable, usado en redes CDMA2000. SMV usa distintos modos de operación que son seleccionanos sobre la base de las características de la voz usada como entrada. Constituyen una de las versiones de codificadores de voz en radiotelefonía. (es) Selectable Mode Vocoder (SMV) is variable bitrate speech coding standard used in CDMA2000 networks. SMV provides multiple modes of operation that are selected based on input speech characteristics. The SMV for Wideband 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. The full rate and half rate are based on the CELP algorithm that is based on a combined closed-loop-open-loop-analysis (COLA). In SMV the signal frames are first classified as: SMV can be also used in 3GPP2 container file format – 3G2. (en) |
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Selectable mode vocoder (es) SMV (ja) Selectable Mode Vocoder (en) |
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