G.722 Audio Coder
for the TMS320C2x, TMS320C5x
by Signals and Software Limited

Software Overview

DSP software which implements the ITU G.722 audio-coding specification. This codes wideband audio 
(50–7000 Hz, sampled at 16 kHz) to one of three bit rates: 48, 56, or 64 kb/s. G.722 is a mandatory 
coding scheme for wideband audio under the ITU specification H.320 for videoconferencing 
applications.

Features and Benefits

The G.722 specification uses a sub-band ADPCM (adaptive differential pulse code modulation) 
algorithm. Compared to the original, the performance at the various bit rates for a single 
encode/decode and for multiple tandem codings and decodings is judged to be as follows:
64 kb/s	No distortion, some slight loss of high-frequency definition, passes music signals equally 
as well as speech. Tandem performance is excellent, more than six encodes/decodes being possible 
before noticeable degradation from a single coding/decoding exists.
56 kb/s	Very little degradation compared to the 64-kb/s rate. Tandem performance is that six 
tandems are possible before degradation starts.
48 kb/s	Some degradation from 64 kb/s with some distortion being present. Tandem performance is 
four times before degradation starts.

The software passes the ITU G.722 test vectors.

Processor and System Requirements

G.722
Program Memory (Words)
Data Memory (Words)
Processing Load (MIPS)
Encoder + decoder
1100
172
9.5
Encoder only
680
85
5.1
Decoder only
650
87
4.4

Usage Limitations or Performance Considerations

•	The software consists of four subroutines: an initialization routine and a processing routine for 
each of the encoder and decoder functions. The initialization routines, which also select the bit 
rate, are normally called only on DSP reset or change of coding rate. The audio input and output 
format is 16-kHz linear, and the processing routines are called once per pair of 16-kHz samples, 
since codewords are generated every two samples. The encoder converts each pair of input samples 
into a codeword (6 to 8 bits, according to the rate), which is used by the decoder to reconstruct 
the two samples.
•	Applications for this algorithm are speech and music compression for high-quality digital video 
and audio conferencing, desktop videophone/PC terminal audio, wideband ISDN telephones, 
high-quality speech, and music storage.

Availability

Now, under licence, for a one-off payment and/or royalties depending on the commercial application. 
An Application Note is available. Support consultancy for code integration is also available.

Company Background and Contact Information

Signals and Software Limited (SASL), based in Harrow, Middlesex, UK is a design consultancy 
specializing in the area of Digital Signal Processing (DSP). From concept and algorithm design 
through to real-time DSP implementation, SASL is able to offer its clients fast and cost-effective 
solutions to their DSP needs. Services include: feasibility studies, DSP software to order, DSP 
research and algorithm design, computer simulations (C or PASCAL), and hardware design. In support 
of these services, SASL offers a range of "off-the-shelf" software that includes audio/speech 
coding, modems, acoustic echo cancellation, video coding, and general telecommunications functions. 
Key technology areas include: GSM/PCN mobile comms, video conferencing, video telephony, and 
PSTN/ISDN voice and data transmission.

Contact:	David Morley
		3 Jardine House
		Bessborough Road
		Harrovian Business Village
		Harrow, Middlesex, HA1 3EX
		United Kingdom
		+44 (0) 181 426 9533
		Fax: +44 (0) 181 869 1182
		e-mail: davem@sasl.demon.co.uk