Call Today 716.688.4675

GSM 06.20 Half Rate (HR) Codec

VOCAL offers the GSM 06.20 Half Rate (HR) codec  as a real-time implementation that can be configured to support multichannel applications. GSM 06.20 software may be licensed as a standalone algorithm, a library, and with a VoIP stack for integration options with user applications. Contact us to discuss your GSM 06.20 HR vocoder application requirements.

download brochure

The GSM 06.20 speech compression source code is optimized to run on DSPs and conventional processors from TI, ADI, AMD, Intel and other leading vendors. GSM 06.20 codec is also available as a custom design to meet your unique application requirements.

GSM 06.20

GSM 06.20 uses the VSELP (Vector-Sum Excited Linear Prediction) algorithm. The VSELP algorithm is an analysis-by-synthesis coding technique and belongs to the class of speech coding algorithms known as CELP (Code Excited Linear Prediction).

GSM 06.20 describes the detailed mapping between input blocks of 160 speech samples in 13 bit uniform PCM form into encoded blocks of 112 bits and from encoded blocks of 112 bits to output blocks of 160 reconstructed speech samples. The sampling rate is 8,000 sample/s leading to an average bit rate for the encoded bit stream of 5,6 kbit/s. The coding scheme is called Vector Sum Excited Linear Prediction (VSELP) coding.


  • Full and half duplex modes of operation
  • Passes ETSI test vectors
  • Compliant with GSM 06.20 Recommendation
  • Optimized for high performance on leading edge DSP architectures
  • Multichannel implementation
  • Multi-tasking environment compatible


  • DAA interface using linear codec at 8.0 kHz sample rate
  • Direct interface to 8.0 kHz PCM data stream (A-law or μ-law)
  • North American/International Telephony (including caller ID) support available
  • Simultaneous DTMF detector operation available – (less than 10 talkoff hits on Bellcore test tape set)
  • MF tone detectors, general purpose programmable tone detectors/generators available
  • Data/Facsimile/Voice Distinction available
  • Common compressed speech frame stream interface to support systems with multiple speech coders
  • Dynamic speech coders selection if multiple speech codecs available
  • Can be integrated with Acoustic Echo Canceller, G.168 Line Echo Canceller and Tone Detection/Regeneration modules
  • Available with VoIP stack



VOCAL’s software is available for the following Platforms. Please contact us for specific GSM 06.20 vocoder supported platforms.

  • Texas Instruments – C6000 (TMS320C62x, TMS320C64x, TMS320C645x, TMS320C66x, TMS320C67x), DaVinci, OMAP, C5000 (TMS320C54x, TMS320C55x)
  • Analog Devices – Blackfin, TigerSHARC, SHARC
  • PowerPC
  • MIPS – MIPS32, MIPS64, MIPS4Kc
  • ARM – ARM7, ARM9, ARM9E, ARM10E, ARM11, StrongARM, ARM Cortex-A8, Cortex-M1
  • Intel / AMD x86, x64 (both 32 and 64 bit modes)

Operating Systems

VOCAL’s GSM 06.20 HR vocoder software is available for the following Operating Systems:

  • Google Android
  • Apple iOS / iPhone / iPad & MacOS
  • Unix,  Linux, μClinux, BSD
  • Microsoft Windows ACM / RTC / CE / Mobile
  • Symbian
  • eCOS / eCOSPro
  • Wind River VxWorks
  • Green Hills Integrity
  • Micrium μCOS

Please contact us for other supported Operating Systems.

More Information

VOCAL Technologies, Ltd.
520 Lee Entrance, Suite 202
Amherst New York 14228
Phone: +1-716-688-4675
Fax: +1-716-639-0713