ITU G.723
CELP Vocoder
for TMS320C5x
by DSP Software Engineering, Inc.

Software Overview

DSP Software Engineering, Inc.'s (DSPSE) G.723 offering is a real-time full-duplex implementation 
of the new ITU G.723 dual-rate vocoder for the TMS320C5x DSP. G.723 is an international standard 
for videoconferencing applications. It encodes 8-kHz sampled-speech signals for transmission over 
either 6.4- or 5.3-kbps channels.  G.723 provides approximately 4 kHz of toll-quality speech 
bandwidth.
G.723 encodes 240 sample frames of 16-bit linear-PCM data into either 12 16-bit code words for the 
6.4-kbps rate or 10 16-bit code words for the 5.3-kbps rate. G.723 has numerous applications in 
products that require high-quality-speech coding over a narrow band digital channel. These include 
videoconferencing, digital telephony, and multimedia products.

Features and Benefits

•	Full-ITU-compliant implementation on a single Texas Instruments TMS320C5x DSP
•	Separate encoder and decoder function calls for half- or full-duplex operation
•	Reentrant, object-based structure for simple single- and multi-channel system integration
•	Will run on the low-cost TMS320C52
•	7.5-ms algorithmic and a 97.5-ms channel delay making it acceptable for voice over data 
applications
•	Can be used with a number of real-time operating systems such as SPOX

Processor and System Requirements

•	Devices supported: TMS320C5x
•	Algorithm category: Vocoder
•	Requirements:
All memory requirements are in units of 16-bit words. The MIPS ratings presented require the listed 
amounts of dual-access RAM (DARAM), zero-wait-state program and data memory, and a processing frame 
size of 240 samples. All measurements were made using an executable demonstration built for a 
third-party PC plug-in board.
Function
MIPS
On-Chip DARAM
External Data RAM
External Data/Program ROM
Encoder (half duplex)
30.5/26
1.0 k
2.00 k
**19.5 k
Decoder (half duplex)
2.8/2.9
1.0 k
1.00 k
**19.5 k
Full Duplex*
30.28/28.9
*1.0 k
3.00 k
**19.5 k
*    The on-chip DARAM in only used during the function call. There is no historical data.
**   Significant portions of DARAM, read-only program, and data are shared by the encoder and 
decoder.

User Functions

The G.723 implementation consists of two independent, C-callable functions that perform encoding 
and decoding operations.  It also includes functions that reflect the implementation's object-based 
interface.  The encoder and decoder interface with arrays of 240 16-bit words of linear-PCM samples 
and 12 or 10 16-bit code words.
G.723 Functions
G723_Ecreate (...)
Initializes data memory for encoder
G723_Dcreate(...)
Initializes memory for the decoder
G723_Encode (...)
Encodes an array of 240 16-bit linear-PCM samples into a frame of code words
G723_Decode (...)
Decodes a frame of code words into an array of 240 16-bit linear PCM samples

Algorithm Verification

•	Call DSPSE for verification details

Availability

•	Source and object code currently available for licensing.

Company Background and Contact Information

DSP Software Engineering, Inc. is a leading provider of highly-complex digital-signal-processing 
software.
Contact:	DSP Software Engineering, Inc
		175 Middlesex Turnpike
		Bedford, MA 01730  USA
		(617) 275-3733
		Fax: (617) 275-4323
		e-mail:  info@dspse.com
		www:  http://www.dspnet.com