Low-Complexity
ADPCM Voice Coder
by D2 Technologies, Inc.

Software Overview

D2's Low-Complexity (LC) ADPCM voice-coder algorithm module compresses either linear or codec voice 
data to 32 kbps at significantly lower complexity than ITU-T G.726 standard coders. The quality of 
the LC ADPCM meets the "toll quality" requirements of speech applications.
Designed to the VP Open interface, the LC ADPCM voice-coder module easily integrates with other VP 
Open modules, runs in real-time concurrently with other VP Open modules, and handles any number of 
voice ports assigned to the DSP. Like all of D2's algorithm modules, LC ADPCM voice coder consists 
of robust software that is rigorously tested.

Features and Benefits

•	Compresses the voice data to 32 kbps
•	Extremely low complexity
•	"Toll quality" for speech applications
•	Accepts telephone-band codec or linear data

Processor and System Specifications

•	Devices supported: TMS320C2xx, TMS320C5x
•	Algorithm category: Vocoder
•	DSP resource required:
TMS320C2xx (Est.)
TMS320C5x
Program memory
0.35 kwords
0.3 kwords
Data memory/voice port
5 words
5 words
Processor loading
worst case
Encoder: 0.8 MIPS
Decoder: 0.7 MIPS
Encoder: 0.7 MIPS
Decoder: 0.57 MIPS

Usage Limitations or Performance Considerations

•	The host, voice data input and output, memory allocation, and module to module communication 
interfaces must conform to VP Open as described in the VP Open Software Interface Specification.

Algorithm Verification

D2's LC ADPCM voice coder algorithm module is validated through the following suite of tests:
•	Voice input tests with different telephone band voice samples and background noise conditions
•	Mean Opinion Score (MOS) test per ITU-T P.80 specification for Absolute Category Rating
•	Non-voice input tests with artificial signal such as tones and extreme values used to test 
numerical stability
•	Code error tests for stationary and non-stationary errors
•	VP Open interface validation – the LC ADPCM module is integrated with other VP Open modules and 
tested concurrently in real-time on the D2 VDS50 system for multiple voice ports

Availability

Currently available for the TMS320C5x. A demonstration package is available for the TI EVM50 DSP 
board. A demonstration cassette tape and a live over-the-phone demonstration are also available. 
Implementation for the TMS320C2xx will be available 2Q 1996.

Company Background and Contact Information

D2 Technologies, Inc. was founded by David Y. Wong and David M. Lindsay to help companies innovate 
telecommunications and information products with voice processing technology, which include 
telephony and voice algorithms, real-time system software, and development services.
Contact:	D2 Technologies, Inc.
		Attn:  Product Sales
		104 West Anapamu Street, Suite J
		Santa Barbara,  CA 93101
		(805) 564-3424
		Fax:  (805) 966-2144
		e-mail:  sales@d2tech.com