Telco DTMF Generator/Detector
for TMS320C3x/'C4x
by DSP Software Engineering, Inc.

Software Overview

The DTMF software is an implementation of a DTMF generator and DTMF detector for the TMS320C3x. 
Dual-Tone Multi-Frequency (DTMF) is an international signaling standard for telephone digits 
(number buttons). The DTMF generator function generates standard telephone digits as the sum of 
sinusoids corresponding to a row and column frequency for each digit. The DTMF detector function 
checks incoming digit signals and uses a series of tests to decode them.
The DTMF software generates and detects linear PCM samples at any sample rate that is an integer 
multiple of 4-kHz.  DTMF has a variety of uses in modern telephone systems. It provides a means of 
data entry and menu selection for numerous applications, including financial transactions, business 
directories, voice mail, and many other menu-driven operations that respond to digits entered from 
a telephone.

Features and Benefits

•	Detects up to 32 channels on a 33-MHz and 48 channels on a 50-MHz TMS320C3x
•	Independent C-callable generator and detector functions
•	User-specified processing frame size.
•	SPOX compatible
•	Object-based interface

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 and a processing frame size of 20 
samples at 8 kHz. All measurements were made using an executable demonstration built for a third 
party PC plug-in board.
Function
Avg MIPS
Chip RAM
Data
Program
Generator
0.52
25
0.4 k
1.0 k
Detector 
0.42
0
0.7 k
0.4 k
Generate & Detect
0.94
25
1.1 k
1.4 k
* Frame size of 20 samples - performance increases with larger frames.

User Functions

The DTMF implementation consists of two independent, C-callable functions that perform generation 
and detection operations. It also includes functions that reflect the implementation's object-based 
interface. The generator and detector interface with arrays of linear PCM samples and DTMF digits.
DTMF Generator
DTG_create (...)
Dynamically allocates and initializes data memory for generator
DTG_delete (...)
Frees generator's usage of dynamically-allocated data memory
DTG_gen (...)
Generates a frame of linear PCM samples for a specified digit
VoiceWave Decoder
VWD_create (...)
Dynamically allocates and initializes data memory for detector
VWD_delete (...)
Frees detector's usage of dynamically-allocated data memory
VWD_decode (...)
Returns DTMF digit-status detected for each frame of 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