ITU G.728
LD-CELP Vocoder
for TMS320C5x
by DSP Software Engineering, Inc.

Software Overview

The G.728 LD-CELP vocoder software is an implementation of ITU (formerly CCITT) G.728 for the 
TMS320C5x. G.728 is an international standard for encoding 8-kHz sampled-speech signals for 
transmission over 16-kbps channels. G.728 provides approximately 4 kHz of speech bandwidth.
G.728 encodes 5 sample frames of 16-bit linear-PCM data into 10-bit code words.  G.728 has numerous 
applications in products that require high-quality speech coding with very-low delay at 16 kbps. 
These include videoconferencing, digital telephony, and multimedia products.

Features and Benefits

•	Full ITU implementation on a single TMS320C5x
•	In-band synchronization capable
•	2.5-ms algorithmic delay (using a 5-sample frame size)
•	Run-time selectable, optimal post filtering
•	Independent, C-callable functions
•	SPOX compatible

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 5 samples. All measurements were made using an executable demonstration built for a 
third-party PC plug-in board.
Function
Avg MIPS
DARAM
Data
Program
Encoder (half duplex)
21.9
0.6 k
1.3 k
6.2 k
Decoder (half duplex)
15.0
0.6 k
1.6 k
7.0 k
Full Duplex*
36.9
1.0 k
2.2 k
10.5 k
*   Significant portions of read-only program and data are shared by the encoder and decoder.

User Functions

The G.728 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 16-bit linear-PCM samples and 10-bit 
code words.
G.728 Functions
G728_create (...)
Initializes data memory for encoder/decoder
G728_decode (...)
Decodes a frame of code words into a frame of 16-bit linear-PCM samples
G728_encode (...)
Encodes a frame of 16-bit linear-PCM samples into a frame of code words

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 (DSPSE), founded in 1989, is a leading provider of highly-complex 
digital-signal-processing software used in telecommunications and multimedia applications such as 
computer telephony, digital wireless, PSTN, and satellite communications, and videoconferencing.

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