USFS 1016 CELP Vocoder
for TMS320C5x
by DSP Software Engineering, Inc.

Software Overview

The CELP vocoder software is an implementation of USFS 1016 CELP for the TMS320C5x. USFS 1016 CELP 
is a US Federal Government standard for encoding 8-kHz sampled speech signals for transmission over 
4.8-kbps channels. CELP provides approximately 4 kHz of speech bandwidth and has an algorithmic 
delay of 15 ms.
USFS 1016 CELP encodes frames of 240 linear-PCM samples into frames of 18, 8-bit code words (144 
bits). CELP has numerous applications in products that require low digital bandwidth coding, such 
as voice mail, answering machines, satellite communications, and high-compression digital 
recording.

Features and Benefits

•	Additional, non-standard rate of 7.2 kbps (160 samples per frame)
•	In-band synchronization capable
•	C-callable encoder and decoder functions
•	SPOX compatible
•	Optimal postfiltering, dynamically selectable

Processor and System Requirements

•	Devices supported: TMS320C5x
•	Algorithm category: Vocoder
•	Requirements:
All memory requirements are in units of 16-bit words. The MIPS ratings presented require the listed 
amounts of dual-access RAM (DARAM), zero-wait-state program and data memory, and a processing frame 
size of 240 samples. All measurements were made using an executable demonstration built for a 
third-party PC plug-in board.
Function
Avg MIPS
DARAM
Data
Program
Encoder (half duplex)
14.4
0.7 k
2.9 k
6.9 k
Decoder (half duplex) 
2.6
0.7 k
1.3 k
4.2 k
Full Duplex*
17.0
1.4 k
4.2 k
9.2 k
* CELP encoder and decoder share significant portions of read-only program memory.

User Functions

The CELP implementation consists of two C-callable functions that perform encoding and decoding 
operations. The encoder and decoder interface with arrays of linear-PCM samples and 8-bit code 
words.
CELP Encoder/Decoder
ana (...)
Encodes a frame of linear-PCM samples into a frame of code words
syn (...)
Decodes a frame of code words into a frame of linear-PCM samples

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. 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