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G.726 is an ITU-T ADPCM speech codec standard covering the transmission of voice at rates of 16, 24, 32, and 40 kbit/s. It was introduced to supersede both G.721, which covered ADPCM at 32 kbit/s, and G.723, which described ADPCM for 24 and 40 kbit/s. G.726 also introduced a new 16 kbit/s rate. The four bit rates associated with G.726 are often referred to by the bit size of a sample, which are 2, 3, 4, and 5-bits respectively.

The most commonly used mode is 32 kbit/s, which doubles the usable network capacity by using half the rate of G.711. It is primarily used on international trunks in the phone network and is the standard codec used in DECT wireless phone systems. The principal application of 24 and 16 kbit/s channels is for overload channels carrying voice in digital circuit multiplication equipment (DCME). The principal application of 40 kbit/s channels is to carry data modem signals in DCME, especially for modems operating at greater than 4800 bit/s.

SPIRIT G.726 conforms to ITU-T G.726 recommendation that specifies speech compression and decompression at rates of 16, 24, 32 and 40 Kbps based on Adaptive Differential Pulse Code Modulation (ADPCM). It can be effectively used for audio and speech compression in such applications as speech storing, digital circuit multiplication and telephony applications.


  • Fully bit exact with ITU-T G.726
  • Sample-by-sample or block based analog input
  • 16, 24, 32 or 40 Kbps bit stream rate
  • A-law, μ-law and 14-bit uniform 8 kHz PCM input/output
  • Input/output samples format: Linear PCM, 8 kHz, 16 bits. Both sample-by-sample and block based processing supported
  • Can process blocks of different lengths
  • Both MIPS and memory optimized versions are available
  • Very simple application interface
  • eXpressDSP compliant. Code is reentrant, supports multithreading and dynamic memory allocation

To integrate SPIRIT G.726 into your video conferencing application or service please send us a request at sales@spiritdsp.com

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Other components for IP voice and video calling apps provided by SPIRIT: