TIA TIA-102.BABB

This document specifies the procedures to be employed to test that implementations of TIA-102.BABA compatible speech codecs comply with the standard. This speech codec is the Improved Multi-Band Excitation (IMBE^TM, a trademark of Digital Voice Systems Inc.) system described in TLA-102.BABA, Project 25 Vocoder Description. The IMBE speech codec is used to digitally encode the speech signal and provide forward error control for transmission at a data rate of 7200 b/s.

The need for this standard arises from the fact that implementations of speech coders do not need to have identical numerical precision in the internal arithmetic operations to be compatible. Since individual designers implement algorithms in different manners, it is not possible to create a standard set of test vectors to assess conformance to a standard. This document describes a series of tests that are used to test conformance to the specification. These tests do not necessarily ensure that the speech codecs operate satisfactorily under all possible input signals and it is still a requirement of the manufacturer to ensure that his implementation operates in a consistent manner. The purpose of these tests is to test for standard compliance. The manufacturer is encouraged to provide the highest possible performance but it is not the purpose of these tests to determine that performance.

The testing of the codecs is based upon subjective tests which employ listening tests to judge overall speech quality.

This standard takes the approach of defíning a reference speech codec and then each manufacturer tests his implementation relative to the reference. All possible combinations of test codec to reference codec are evaluated. The reference speech codec is based upon the Digital Voice Systems Incorporated implementation of the IMBE algorithm on the VC-20 Project 25 hardware card.