VoIP Voice and Fax Signal Processing

19.5 VOICE PROCESSING COMPLEXITY

In this section, an overview on processing requirements is given. The major computational intensive modules for VoIP voice chain are codecs (G729AB, G.723.1, and wideband G.722, G.729.1, G.722.2), echo cancellers for narrow-band and wideband, dual-tone multifrequency (DTMF), and PLC. The other modules of voice activity detection (VAD)/comfort noise generation (CNG), jitter buffers, tone generation, and various tone detection take less processing. A fax chain with group-3, V.17 requires higher processing. In super group-3, V.34 requires more processing.

For voice processing, the DSPs selected will typically have multiple multiplier and accumulator (MAC) processing units. The number of parallel multipliers determines the speed of processing. The older families of DSPs such as the 218x [URL (ADI-218x)] and TI-54x [URL (TI-54x)] have a single multiplier unit. Later families, such as the TI-55X and Blackfin, have dual multiplier units. The TI-64X [URL (Encore-G729AB)] and Starcore families have complex processing units that work like more than two independent multiplier units.

Many voice processing algorithms can derive significant performance benefits from dual multiplier processor architecture—in some cases as much as 40% to 50%. For example, consider G.729AB [ITU-T-G.729A (1996), ITU-T-G.729B (1996)] processing from reference [URL (Encore-G729AB)]. A single multiplier processor such as the ADSP218x or the TI-54x requires about 12.5 to 13 MCPS (MCPS ...