ITU G.728
Low-Delay CELP Vocoder
for TMS320C3x/'C4x
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 
TMS320C3x. 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. DSPSE's G.728 
implementation offers two additional, non-standard bit rates of 12.8 and 14.4 kbps (8 and 9-bit 
code words respectively). 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

•	User-selectable processing frame size (any multiple of 5 samples)
•	In-band synchronization capable
•	2.5-ms algorithmic delay (using a 5-sample frame size)
•	Dynamically-adjustable codebook size
•	Object-based interface
•	Run-time selectable, optimal post filtering
•	Independent, C-callable functions
•	SPOX compatible

Processor and System Requirements

•	Devices supported: TMS320C3x, TMS320C4x
•	Algorithm category: Vocoder
•	Requirements:
All memory requirements are in units of 32-bit words. The MIPs ratings presented require the listed 
amounts of on-chip, 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*
Chip RAM
Data
Program
Encoder (half duplex)
10.7
0.9 k
0.3 k
9.1 k
Decoder (half duplex)
6.8
0.9 k
0.6 k
8.6 k
Full Duplex**
17.5
1.8 k
0.9 k
16 k
*   Significant portions of read-only program and data are shared by the encoder and decoder.
* * MIPs may be reduced by operating with a larger processing frame size. 

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 8-, 9-, 
or 10-bit code words.
G.728 Encoder
G728E_create (...)
Dynamically allocates and initializes data memory for encoder
G728E_delete (...)
Frees encoder's usage of dynamically-allocated data memory
G728E_encode (...)
Encodes a frame of 16-bit linear PCM samples into a frame of code words
G.728 Decoder
G728D_create (...)
Dynamically allocates and initializes data memory for decoder
G728D_delete (...)
Frees decoder's usage of dynamically-allocated data memory
G728D_decode (...)
Decodes a frame of code words into a frame of 16-bit linear PCM samples

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