USFS 1015 
LPC10e Vocoder V52
for TMS320C5x
by DSP Software Engineering, Inc.

Software Overview

The LPC10e vocoder software is an implementation of USFS LPC10e for the TMS320C5x. LPC10e is a US 
Federal Government standard for encoding 8-kHz sampled speech signals for transmission over 
2.4-kbps channels. LPC10e provides approximately 4 kHz of speech bandwidth. LPC10e has an 
algorithmic delay of 50 ms.
LPC10e encodes frames of 180 linear-PCM samples into 54-bit code words. LPC10e has numerous 
applications that require a very-low-digital bit rate for communications or storage, such as secure 
communications, tactical communications, and voice storage.

Features and Benefits

•	Full-duplex, real-time LPC10e operation
•	C-callable functions
•	Full compliance with US Federal Standard 1015
•	SPOX compatible
•	Single TMS320C5x implementation

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, zero-wait-state program and data memory, and a processing frame size of 
180 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)
4.4
32
4.8 k
4.8 k
Decoder (half duplex)
4.3
32
2.5 k
5.5 k
Full Duplex*
8.7
32
5.5 k
7.4 k
* LPC10e encoder and decoder share significant portions of data and program memory.

User Functions

The LPC10e implementation consists of two C-callable functions that perform encoding and decoding 
operations. It also includes an initialization function. The encoder and decoder interface with 
arrays of  linear PCM samples and 16-bit code words through embedded input and output queues.
LPC10e Encoder/Decoder
initial (...)
Dynamically initializes data memory for encoder and decoder
analysis (...)
Encodes a frame of linear-PCM samples into a frame of code words
synth (...)
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 (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. 
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