TIA/EIA-102.BABC:1999

This document specifies one method that may be employed to test
that implementations of TIAEIA-l02. BABA compatible speech codecs
meet recommended minimum performance requirements. This speech
codec is the Improved Multi-Band Excitation (IMBE^TM )
system described in [2]. The IMBE speech codec is used to digitally
encode the speech signal at 4400 bps or decode the speech signal
back to analog audio. Forward error correcting codes (FEC) are
added to this to increase the signaling rate to 7200 bps. Most of
the tests in this document are for the speech codec, and some of
the tests verify the conformance of the FEC. All of the tests use
an interface operating with the combined FEC/codec signal at 7200
bps.

The need for this procedure arises from the fact that
implementations of speech coders do not have to be bit exact to
achieve compatibility. 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 which are used to test
conformance to specific aspects of the specification. These test 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 minimum performance levels and the manufacturer should
attempt to provide the highest performance possible.

The testing of the codecs described in this document is based
upon quantitative tests with specific pass/fail criteria. The major
purpose of these tests is not to assess the performance between one
manufacturer's encoder and decoder, but to assess the Performance
between any pairing of manufacturer's encoders and decoders. This
interoperability issue is of a critical nature to end users. The
overall purpose of this standard is to provide a means for
measuring performance levels while trying to ensure proper
inter-operability with other manufacturer's equipment.

The issue of inter-operation can only be definitively answered
by testing all combinations of encoder/decoder pairings. With the
number of equipment manufacturers expected to supply equipment this
may well be a prohibitive task. This standard takes the approach of
defining a reference speech codec and then each manufacturer tests
his implementation relative to the reference. Specific parameters
identified by the developer of the speech codec are then compared
against the reference. The speech codec is said to be in
conformance once the objective performance requirements have been
satisfied.

This document requires use of proprietary test equipment which
may be purchased from Digital Voice Systems Incorporated. An
alternative method of testing using Mean Opinion Scores (MOS) is
described in [4].