IDEC™-II
Acoustic Echo Canceller for TMS320C3x/'C4x
by DSP Software Engineering, Inc.

Software Overview

Integrated Dynamic Echo Cancellation (IDEC-II, a PICTURETEL Technology) is a software solution for 
acoustic echo cancellation, noise cancellation, and automatic gain control in 
audio/videoconferencing applications. It adaptively cancels acoustic echoes arising in hands-free 
teleconferencing, providing high-quality, full-duplex speech communications. IDEC employs patented 
techniques to eliminate switching, glitching and speech dropouts producing completely natural 
two-way conversation.  Noise suppression eliminates the background noise from air conditioning 
systems, overhead projection fans, and computer fans while AGC keeps the loudness of voices 
constant throughout the conversation.
IDEC-II performance specifications are compatible with the ITU's G.167 series recommendations on 
echo cancellers for telephony.

Features and Benefits

•	Real full-duplex speakerphone communications
•	Automatic Noise Suppression up to 
12 dB
•	Automatic training with fast, continuous adaptation
•	Total echo cancellation: 60 dB, maximum
•	Operation at positive room acoustic gain
•	Room acoustic gain: up to 10 dB, nominal
•	Configurable for 3.5-kHz or 7-kHz operation
•	Audio-processing bandwidth @ 8-kHz sample rate: 125–3625 Hz ±2 dB
•	Convergence rate of adaptation: 
30 dB/sec
•	Audio-processing bandwidth @ 16 kHz sample rate: 125–7126 Hz ±2 dB
•	Adaptive (only) echo cancellation: 
> 30 dB

Processor and System Requirements

•	Devices supported: TMS320C3x, TMS320C4x
•	Algorithm category: Telecommunications
•	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, a processing frame size of 4 ms, and 
an 128-ms echo length.
Function
Avg MIPS
Chip RAM
Data
Program
8-kHz operation
< 8.4
2.0 k
< 18.0 k
< 7.0 k
16-kHz operation
< 11.0
2.0 k
< 18.0 k
< 7.0 k

User Functions

The IDEC implementation consists of one C-callable function that performs echo-cancellation 
operation. IDEC interfaces with arrays of 16-bit linear PCM samples.
IDEC-II
IDECII_create (...)
Dynamically allocates and initializes data memory for canceller
IDECII_delete (...)
Frees canceller's usage of dynamically-allocated data memory
IDECII_process (...)
Inputs are TX and RX PCM to/from codec, output is echo-cancelled RX PCM

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. 
DSPSE sells its products to OEMs and directly to manufacturers of telecommunications products. 
DSPSE provides the complete solution to your DSP needs with DSP solution software packages and 
individual DSP software component algorithms and expert service.
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