Time Scale Modification
by Atlanta Signal Processors, Inc.

Software Overview

Time scale modification code independently alters the speed and pitch of an input audio signal. 
That is, one could alter the speed without altering the pitch, alter the pitch without altering the 
speed, or change speed and pitch simultaneously. The `C31 algorithm works very well with one or two 
speaker speech, with background noise, and with solo instruments. Tests were performed in 
non-real-time at higher sampling frequencies; the results for more complex signals, such as 
multiple instrument music, performed significantly better.
Applications that can benefit from time scaling include voice mail (to speed up lengthy or slowly 
spoken messages or to slow messages down for fast talkers or transcription); text-to-speech; and 
music for sampling keyboards, special effects, or cropping segments for the audio and video 
production industry.

Features and Benefits

•	Code is C callable and relocatable
•	50–200% pitch or speed changes at 
8 kHz on a single TI TMS320C3x DSP
•	Independently varies pitch or speed 
•	8-kHz real-time operation

Processor and System Specifications

•	Program memory: 36 kwords
•	Data memory: 6 kwords
•	33-MHz CPU loading (static memory): 100%
•	Sampling rate: 8 kHz
•	Minimum analog requirement:  TLC32044 or similar 14-bit, 8-kHz AIC
•	Ready to run on the Elf DSP Platform from Atlanta Signal Processors
•	Portable to any TMS320C3x target platform

Usage Limitations or Performance Considerations

•	At 8 kHz, this algorithm can work in real-time, on any length signal, with 50% to 200% pitch 
changes. With adequate buffers, the algorithm can change speed 50% to 200% with real-time input or 
output.

Algorithm Verification

•	There are no international standards for this algorithm. However it has been extensively tested.

Availability

•	Written by and available from Atlanta Signal Processors.

Company Background and Contact Information

Atlanta Signal Processors was founded in 1981 by Ronald W. Schafer, Thomas P. Barnwell III, and 
Russell M. Mersereau, three Professors of Electrical Engineering at the Georgia Institute of 
Technology with over 80 years of experience in the field. The company has focused its efforts on 
developing tools for professional signal-processing design engineers and now offers digital 
signal-processing hardware and software products to DSP designers worldwide.
Contact:	Atlanta Signal Processors, Inc.
		1375 Peachtree St. NE, Suite 690
		Atlanta, Georgia  30309-3115
		(404) 892-7265
		Fax: (404) 892-2512
		e-mail: aspi@aspi.com