USFS 1015 LPC10e 
Vocoder V52
for TMS320C3x/'C4x
by DSP Software Engineering, Inc.

Software Overview

The LPC10e vocoder software is an implementation of USFS LPC10e for the TMS320C3x. 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 67.5 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

•	Object-based interface
•	C-callable functions
•	In-band synchronization capable
•	SPOX compatible

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 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)
4.9
1.8 k
3.1 k
3.9 k
Decoder (half duplex)
3.8
1.8 k
3.1 k
3.9 k
Full Duplex*
8.7
1.8 k
3.1 k
3.9 k
* LPC10e encoder and decoder software are contained in one module that is operable in half duplex.

User Functions

The LPC10e 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 1-bit code words.
LPC10e Encoder/Decoder
LPC_create (...)
Dynamically allocates and initializes data memory for encoder and decoder
LPC_delete (...)
Frees encoder's usage of dynamically-allocated data memory
LPC_encode (...)
Encodes a frame of linear PCM samples into a frame of code words
LPC_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