Variable-Rate
CELP Coding
by HotHaus Technologies

Software Overview

The HotHaus Variable-Rate CELP (VRCELP) coding software module is designed to provide speech coding 
for applications that require good quality, efficient, and low-bit-rate speech coding. VRCELP 
provides for a fixed-rate mode of operation at an 8-kbps rate, and a variable-rate mode of 
operation with a rate of 
4–5 kbps for standard speech.
In variable-rate mode, each speech frame is analyzed by a frame classifier and classified as one of 
voiced, unvoiced, transition, or silence, in order to determine the desired coding rate. The system 
switches between three distinct codec configurations: 8.0 kbps for voiced and transition frames, 
4.3 kbps for unvoiced frames, and 667 bps for silence frames. This yields an overall average rate 
of 4.2 kbps based on averaging of typical male/female speech files with 40% silence.

Features and Benefits

•	Operates in either 8-kbps fixed-rate mode or 4–5 kbps variable-rate mode
•	MOS score of 3.5 in fixed-rate mode and 3.4 in variable-rate mode
•	Requires 11 MIPS in fixed-rate mode and 12 MIPS in variable-rate mode
•	Fully re-entrant, each extra port requires only additional RAM space
•	Uses 17.8 MIPS

Processor and System Requirements

Runs on Texas Instruments TMS320C5x family of DSPs.
Requires 8-KHz sampling rate.

Usage Limitations or Performance Considerations

None

Algorithm Verification

MOS testing performed using VSELP as a reference

Availability

Immediately on 'C5x.

Company Background and Contact Information

HotHaus are experts in TI fixed-point DSP software algorithms for telecommunications. HotHaus' 
algorithms are ideally suited for advanced telecommunications products such as feature phones, PBX 
or key systems, and general computer telephony products.
HausWare is the flagship of the company's product line, and it provides a complete DSP software 
system architecture specifically for telecommunications products. HausWare is the key to HotHaus 
providing a cost-effective software system solution to our customers.

Contact:	Dan McCallum
		HotHaus Technologies Inc.
		1B - 7218 Progress Way
		Delta BC Canada
		V4G 1H2
		(604) 946-0060
		fax: (604) 946-5811