Speech Time Scaler
for TMS320C3x/'C4x
by DSP Software Engineering, Inc.

Software Overview

The DSPSE time scaler software contains two independent modules for time scaling speech samples:
•	Multi-Rate Filtering Time Scaler (MRF)
•	Pitch-Restoring Time Scaler (TSC)
The Multi-Rate Filtering Time Scaler resamples any signal, allowing the signal to be played back 
faster or slower than real-time. This module is used for fast and slow play operations where the 
signal frequencies are increased or decreased proportionally with the speedup factor.
The Pitch Restoring Time Scaler is used to play back a speech signal faster or slower than 
real-time without changing the speaker's pitch frequency. This module uses a DSPSE proprietary 
algorithm based on advanced vocoder technology. The pitch restoration provides better listener 
comprehension over time scaling without pitch restoration, as provided by the multi-rate filtering 
time scaler.

Features and Benefits

•	Object-based interface
•	Independent, C-callable, object-based functions
•	Sample rate independent
•	SPOX compatible
•	Time scaling from 0.5 to 2.0 times real time (0.5x to 2.0x)

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. All measurements were made using an 
executable demonstration built for a third-party PC plug-in board.
Function
MIPS*
Chip RAM
Data
Program
Time Scaler
2.0 to 8.6
1 k
0.3 k
1.4 k
Multi-Rate Filter
3.0 to 5.7
0
0.1 k
0.4 k
* MIPs vary in the listed range as a function of the time scaling rate and configuration 
parameters.

User Functions

The Time Scaler implementation consists of two independent, C-callable functions that perform 
pitch-restoring time-scaling and multi-rate resampling operations. It also includes functions that 
reflect the implementation's object-based interface. The time scaler and multi-rate filter operate 
on arrays of normalized linear PCM samples.
Pitch Restoring Time Scaler
TSC_create (...)
Dynamically allocates and initializes data memory for the time scaler
TSC_delete (...)
Frees time scaler's usage of data memory
TSC_time_scale (...)
Speed-up or slow-down the input signal without changing pitch
Multi-Rate Filter
MRF_create (...)
Dynamically allocates and initializes data memory for the MRF
MRF_delete (...)
Frees the multi-rate filter's usage of data memory
MRF_filter (...)
Effectively change the sample rate of a 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. 
DSPSE sells its products to OEMs and directly to manufacturers of telecommunications products. 
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