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PSQM testing under ideal conditions yields mean opinion scores of 4.14 for AMR (12.2 kbit/s), compared to 4.45 for G.711 (μ-law).

The complexity of the algorithm is rated at 5, using a relative scale where G.711 is 1 and G.729a is 15.

The residual waveform is coded using algebraic code-excited linear prediction (ACELP).

The LPC parameters are encoded as line spectral pairs (LSP).

Linear predictive coding (LPC) is used to synthesize the speech from a residual waveform.

AMR is a hybrid speech coder, and as such transmits both speech parameters and a waveform signal.

Note that there is 5 ms "dummy" look-ahead delay, to allow seamless frame-wise mode switching with the rest of rates. For other rates, look-ahead delay is 5 ms. For bit-rates of 12.2, there is no "algorithm" look-ahead delay. AMR utilizes discontinuous transmission (DTX), with voice activity detection (VAD) and comfort noise generation (CNG) to reduce bandwidth usage during silence periods.Sampling frequency 8 kHz/13-bit (160 samples for 20 ms frames), filtered to 200–3400 Hz.

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There are a total of 14 modes of the AMR codec, eight are available in a full rate channel (FR) and six on a half rate channel (HR). The new intelligent system allows the network operator to prioritize capacity or quality per base station. In the particular case of AMR this improvement is somewhere around S/N = 4–6 dB for usable communication. This improves the quality and robustness of the network connection while sacrificing some voice clarity. If the radio conditions are bad, source coding is reduced and channel coding is increased. The usage of AMR requires optimized link adaptation that selects the best codec mode to meet the local radio channel and capacity requirements. AMR uses various techniques, such as ACELP, DTX, VAD and CNG. The frames contain 160 samples and are 20 milliseconds long.

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This format is the 3GPP-specified 3GP container format based on ISO base media file format. There also exists another storage format for AMR that is suitable for applications with more advanced demands on the storage format, like random access or synchronization with video.

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Many modern mobile telephone handsets can store short audio recordings in the AMR format, and both free and proprietary programs exist (see Software support) to convert between this and other formats, although AMR is a speech format and is unlikely to give ideal results for other audio. It uses link adaptation to select from one of eight different bit rates based on link conditions.ĪMR is also a file format for storing spoken audio using the AMR codec.

ĪMR was adopted as the standard speech codec by 3GPP in October 1999 and is now widely used in GSM and UMTS. AMR speech codec consists of a multi-rate narrowband speech codec that encodes narrowband (200–3400 Hz) signals at variable bit rates ranging from 4.75 to 12.2 kbit/s with toll quality speech starting at 7.4 kbit/s. The Adaptive Multi-Rate ( AMR, AMR-NB or GSM-AMR) audio codec is an audio compression format optimized for speech coding. Audio compression format, audio file format