USFS 1016 CELP Vocoder
for TMS320C3x/'C4x
by DSP Software Engineering, Inc.

Software Overview

The CELP vocoder software is an implementation of USFS 1016 CELP for the TMS320C3x. USFS 1016 CELP 
is an international 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 rates of 7.2 and 9.6 kbps (160- and 120-sample frame sizes, 
respectively)
•	Dynamically adjustable codebook size
•	Object-based interface
•	Optimal postfiltering
•	C-callable encoder and decoder functions
•	SPOX compatible
•	User-selectable codebook size up to full 512 stochastic vectors

Processor and System Requirements

•	Devices supported: TMS320C3x, TMS320C4x
•	Algorithm category: Vocoder
•	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 240 
samples. All measurements were made using an executable demonstration built for a third-party PC 
plug-in board.
Function
Avg MIPS
Chip RAM
Data
Program
Encoder (half duplex)
12.5
1.7 k
4.0 k
7.2 k
Decoder (half duplex) 
2.0
1.7 k
4.0 k
7.2 k
Full Duplex*
14.5
1.7 k
4.0 k
7.2 k
* CELP encoder and decoder software are contained in one module that is operable in half duplex.

User Functions

The CELP implementation consists of two C-callable functions that perform encoding and decoding 
operations. It also includes functions that reflect the implementation's object-based interface. 
The encoder and decoder interface with arrays of linear PCM samples and 8-bit code words.
CELP Encoder/Decoder
CLP_create (...)
Dynamically allocates and initializes data memory for encoder
CLP_delete (...)
Frees encoder's usage of dynamically-allocated data memory
CLP_encode (...)
Encodes a frame of linear PCM samples into a frame of code words
CLP_decode (...)
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.

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