G.726
Speech Coder
by Atlanta Signal Processors, Inc.

Software Overview

ITU G.726 is a speech coding and decoding standard that provides 4-kHz speech bandwidth switchable 
at 40 k, 32 k, 24 k, or 16 kbps. The full algorithm implementation runs on a single `C31 DSP. The 
implementation passes all digital test sequences provided by the ITU for algorithm verification. 
The G.726 standard specifies an adaptive differential pulse code modulation (ADPCM) system for 
coding and decoding samples. The overall compression ratio is 2.8:1, 3.5:1, 4.67:1, or 7:1 for 
14-bit linear data sampled at 8 kHz and 1.6:1, 2:1, 2.67:1, or 4:1 for 8-bit companded data sampled 
at 8 kHz.
G.726, originally designed as a half-rate alternative to 64-kbps PCM coding (companding), is used 
extensively in all types of digital network equipment for transmission of speech and voiceband 
data. This algorithm is ideal for any application that requires speech compression, or encoding for 
noise immunity, efficient regeneration, easy and effective encryption, and uniformity in 
transmitting voice and data signals.
The 3-, 4-, and 5-bit versions of G.726 were once known as CCITT G.723. This standard was a subset 
of the G.726 algorithm. The 4-bit version of G.726 (32 kbps) was also known as CCITT standard 
G.721. Note that ITU G.723 now refers to a standard for a 5.3 k and 6.4 k bps dual-rate speech 
coder and should not be confused with ITU G.726 or the old CCITT G.723 ADPCM standard.

Features and Benefits

•	Code is C callable and relocatable
•	High-quality 40 k-, 32 k-, or 24 k-bps, 
8 kHz audio coders
•	Fully compliant with ITU G.726 specifications
•	Full-duplex real-time capability on a single TMS320C3x DSP

Processor and System Specifications

•	Memory requirement: 1950 words program, 719 words data
•	Processor loading (33-MHz TMS320C3x, with zero-wait-state SRAM);
50% full duplex, or 22% encoder, 25% decoder, 3% I/O
•	Minimum analog requirement: 
TI TLC32044, TCM29C13, or similar 14-bit, 8-kHz AIC
•	Ready to run on the Elf DSP Platform from Atlanta Signal Processors
•	Portable to any TMS320C3x target platform

Usage Limitations or Performance Considerations

•	None

Algorithm Verification

•	The implementation passes all digital test sequences provided by the ITU for algorithm 
verification.  

Availability

•	Available now through Atlanta Signal Processors.

Company Background and Contact Information

Atlanta Signal Processors was founded in 1981 by Ronald W. Schafer, Thomas P. Barnwell III, and 
Russell M. Mersereau, three Professors of Electrical Engineering at the Georgia Institute of 
Technology with over 80 years of experience in the field. The company has focused its efforts on 
developing tools for professional signal-processing design engineers and now offers digital 
signal-processing hardware and software products to DSP designers worldwide.

Contact:	Atlanta Signal Processors, Inc.
		1375 Peachtree St. NE, Suite 690
		Atlanta, Georgia  30309-3115
		(404) 892-7265
		Fax: (404) 892-2512
		e-mail: aspi@aspi.com