Adaptive Multi-Rate audio codec

About: Adaptive Multi-Rate audio codec is a research topic. Over the lifetime, 1467 publications have been published within this topic receiving 19736 citations. The topic is also known as: AMR & Adaptive Multi-Rate.

Quality control for AMR speech channels in GSM networks

Abstract: In the competitive environment of cellular radio networks, the speech quality experienced by the end user is of vital importance for the network operator. Therefore, the operator needs reliable measures for monitoring and controlling the speech quality. For GSM mobile radio networks employing the adaptive multi-rate (AMR) speech codec, a new instrumental and non-intrusive speech quality metric is proposed. 'Non-intrusive' means that the metric is based only on received transmission parameters, such as the frame erasure rate, and needs neither the original nor the transmitted speech samples. However, for the validation of a new metric, standardized intrusive speech quality measures like PESQ, link-level simulations and field measurements are used. Furthermore, for an improved control of speech quality, a novel AMR mode switching procedure is introduced which outperforms the recommended method of the GSM standard.

Subjective quality evaluation of the 3GPP EVS codec

Abstract: This paper discusses the voice and audio quality characteristics of EVS, the recently standardized 3GPP codec. Comparison to Opus, IETF driven open source codec as well as industry standard voice codecs: 3GPP AMR and AMR-WB, and ITU-T G.718B, G.722.1C and G.719 as well as direct signals at varying bandwidths was made. Voice and audio quality was evaluated with three subjective listening tests containing clean and noisy speech in Finnish language as well as a mixed condition test containing both speech and music intermixed. Nine-scale subjective mean opinion score was calculated for all tested conditions.

Description of GSM enhanced full rate speech codec

Abstract: This paper describes the enhanced full rate (EFR) speech codec that has been standardized by ETSI for the GSM mobile communications system in 1996. The codec was developed jointly by Nokia and the University of Sherbrooke. It operates at 12.2 kbit/s speech coding (source coding) bit-rate and provides speech quality equivalent to that of wireline telephony (G.726 32 kbit/s ADPCM). The algorithm is based on the algebraic code-excited linear prediction (ACELP) technology, using 20 ms speech frames. The GSM EFR speech codec provides substantial quality improvement compared to the current GSM full rate (FR) and half rate (HR) codecs. The old GSM codecs lag far behind wireline quality even in error-free conditions, while the EFR codec provides wireline quality also for the most typical error conditions. With the EFR codec, wireline quality is also sustained in the presence of background noise and in tandem connections (mobile-to-mobile calls). The codec was defined using fixed-point basic operators with complexity estimated at 18 WMOPS (below that of the GSM half-rate codec).

Internet Low Bit Rate Codec

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Multimode variable bit rate speech coding: an efficient paradigm for high-quality low-rate representation of speech signal

Abstract: The speech signal consists of a time-varying ensemble of different types of segments with distinct characteristics, which require different degrees of coding resolution in order to retain an overall high voice quality. A fixed-rate coder can capture such time-varying characteristics only if it operates at a high enough bit rate. At a low bit rate, a fixed-rate coder will not be able to capture all of these various segments well and will fail to render high voice quality. A multimode variable bit rate (VBR) coder uses an arsenal of modes, operating at different bit rates. These modes are designed to represent these different speech segments optimally with the right amount of coding resolution. Thus, a multimode VBR codec adapts the coding mechanism to the input speech and delivers high quality at low (average) rates. This paper presents the essential framework and the unique advantages of a multimode VBR codec and suggests algorithms for the different modes.