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VOCAL’s GSM Adaptive Multi-Rate (AMR) codec is available as a real-time implementation that can be configured to support multichannel applications. GSM AMR software may be licensed as a standalone algorithm, as part of an embedded library suite, or with a VoIP stack for integration with user applications. Contact us to discuss your voice compression application requirements.

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VOCAL’s GSM AMR source code is optimized to run on leading DSPs and conventional processors from TI, ADI, AMD, Intel and other vendors. Our GSM AMR vocoder software may be customized to meet your specific requirements.


Originally developed by ETSI [GSM 06.90], the Adaptive Multi-Rate (AMR) speech codec is also specified for 3GPP [TS 26.071] and ITU [GSM-AMR-WB].

GSM AMR codec describes the detailed mapping from input blocks of 160 speech samples in 13-bit uniform PCM form to encoded blocks of 95, 103, 118, 134, 148, 159, 204, and 244 bits and from encoded blocks of 95, 103, 118, 134, 148, 159, 204, and 244 bits to output blocks of 160 reconstructed speech samples. The sampling rate is 8,000 samples/s leading to a bit rate for the encoded bit stream of 4.75, 5.15, 5.90, 6.70, 7.40, 7.95, 10.2 or 12.2 kbit/s.

The coding scheme for the multi-rate coding modes uses the Algebraic Code Excited Linear Prediction Coder (ACELP); the multi-rate ACELP coder is referred to as MR-ACELP. The transcoding procedure specified in GSM 06.90 is applicable for the adaptive multi-rate full rate and half rate speech traffic channels (TCH) in the GSM system.

GSM AMR Encoder

GSM AMR encoder takes its input as a 13-bit uniform PCM signal either from the audio part of the Mobile Station or on the network side, from the PSTN via an 8-bit A-law or μ-law to 13-bit uniform PCM conversion. The encoded speech at the output of the encoder is delivered to a channel encoder unit. In the receive direction, the inverse operations take place.

GSM AMR Decoder



  • Full and half duplex modes of operation
  • Passes ETSI test vectors
  • Compliant with GSM 06.90 Recommendation
  • Optimized for high performance on leading DSP architectures
  • Multichannel implementation
  • Multi-tasking environment compatible

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VOCAL’s optimized vocoder software is available for the following platforms. Please contact us for specific vocoder supported platforms and performance information.

ProcessorsOperating Systems
  • Texas Instruments – C6xx (TMS320C62x, TMS320C64x, TMS320C645x, TMS320C66x, TMS320C67x), DaVinci, OMAP, C5xx (TMS320C54x, TMS320C55x)
  • Analog Devices – Blackfin, ADSP-21xx, TigerSHARC, SHARC
  • PowerPC, PowerQUICC
  • MIPS – MIPS32, MIPS64, MIPS4Kc
  • ARM – ARM7, ARM9, ARM9E, ARM10E, ARM11, StrongARM, ARMCortex-A8/A9/A15/A3x/A5x/A7x, Cortex-M3/M4/M7/M33
  • Intel / AMD – x86, x64 (both 32 and 64 bit modes)
  • Linux, uClinux, BSD, Unix
  • Microsoft Windows ACM / RTC / CE / Mobile
  • Apple iOS / iPhone / iPad & MacOS
  • Google Android
  • Green Hills Integrity
  • Micrium μCOS
  • Symbian
  • Wind River VxWorks
  • eCOS / eCOSPro