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ITU-T G.726 Speech Coder for the TMS320C55x Generation |
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The ITU-T G.726 Adaptive Differential Pulse Code Modulation (ADPCM) variable rate audio coder is widely used in applications that require robust quality with very little delay. The 8-kHz input to the encoder is either linear data or 8-bit data in A-law or Mu-law format. The output of the encoder is 2, 3, 4, or 5 bits per sample—which corresponds to data rates of 16, 24, 32, or 40 kbps.
An important feature of G.726 is that it can successfully pass signalling tones in addition to fax/modem signals. G.726 supercedes the original ITU-T G.721 and G.723 recommendations. The coder is used in many applications including videoconferencing, speech storage, telephony multiplexing, satellite communications, ISDN, and digital circuit multiplication.
DSP Wizard’s G.726 implementation was designed for low resource requirements without sacrificing quality. It executes at under 6 mips for worst-case linear data. The speed for PCM data is at least 20% faster than any other G.726 c55x implementation available. While it may seem that many DSP software vendors claim to have the best speeds, we can back up our claim. Please compare us to the competition. A 200 MHz c55x chip can support 30 channels.
| G.726 | Encoder | Decoder | Full Duplex |
|---|---|---|---|
| Program Code Memory (Kbytes) | 1.9 | 2.1 | 3.1 |
| Program Table Memory (Kbytes) | 0 | 0 | 0 |
| Data Table Memory (Kbytes) | 1.5 | 3.6 | 3.6 |
| Per Channel Data Memory (Kbytes) | 0.1 | 0.1 | 0.2 |
| Stack Memory (Kbytes) | 0.2 | 0.2 | 0.2 |
| Interrupt Latency (cycles) | 1 | 1 | 1 |
| Typical Call Period (ms) | 10 | 10 | 10 |
| Processor Load: Linear (MHz) | 3.1 | 2.8 | 5.9 |
| Processor Load: Mu/A Law (MHz) | 3.1 | 3.5 | 6.6 |
A linear variant requiring 3.6 Kbytes less memory is also available.