TIA-1017:2005

$29.25

Minimum Performance Specification for the Source-Controlled Variable-Rate Multimode Wideband Speech Codec (VMR-WB) – Service Option 62 for Spread Spectrum Systems

Published By	Publication Date	Number of Pages
TIA	2005	NA

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Category: TIA

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Description

This document specifies the procedures to test implementations
of VMR-WB-compatible variable-rate speech codecs either by
meeting the bit-exact implementation, or meeting recommended
minimum performance requirements. This speech codec is
corresponds to the Service Option 62 described in TIA-1016 [1]. The
VMR-WB codec corresponds to Service Option 62 and is used to
digitally encode the speech signal for transmission at variable
data rates of 13300, 6200, 2700, or 1000 bps. Like some other
speech coding standards, this standard provides a bit-exact method
of testing the codec for minimum performance. In this optional
procedure, a given set of test vectors are input to the test codec,
and the output vectors from the test codec must be bit-exact with
the output vectors generated from the Software Distribution which
is part of this standard. If they are bit-exact, and the test codec
complies with Section 2.1.2, the codec passes the minimum
performance requirement and no further testing is required. The
bit-exact mode of testing, however, is only applicable to codecs
whose design conforms in all respects to the algorithmic
description of the VMR-WB in TIA-1016 [1]. The bit-exact VMR-WB
validation includes specific testing of the OEM VMR-WB to the frame
erasure processing characteristics of the standard VMR-WB. Should
the candidate VMR-WB differ in any of these components, the codec
shall be tested using the objective and subjective tests prescribed
by this standard. That is, VMR-WB compliance of a "test codec" can
be achieved by either:

• Demonstrating bit-exactness according to the procedure
described in Section 3.6, specifically Sections 3.6.5.1 to 3.6.5.4,
or

• Following the objective and subjective testing procedures set
forth in Sections 2.1 and 2.2 of this standard, using processes
additionally defined in Section 3.6, specifically Sections 3.6.5.5
to 3.6.5.8.

With the exception of Section 3.6, the remaining text applies
only to implementations that do not satisfy the requirement for
bit-exactness.

Testing the codec is based on two classes of procedures:
objective tests and subjective tests. In the event that the test
codec fails any of the objective or subjective tests, the test
codec fails the compliance test. Objective tests are based upon
actual measurements from the speech codec function. Subjective
tests are based on listening tests to judge overall speech quality.
The minimum subjective requirement for the test codec is based upon
the ability of the test codec to demonstrate performance equivalent
to or better than that of the VMR-WB floating-point master codec
within a fixed allowable statistical error.

The purpose of the testing is not only to ensure adequate
performance between one manufacturer's encoder and decoder but also
that this level of performance is maintained with operation between
any pairing of manufacturers' encoders and decoders. This
interoperability is a serious issue. Any variation in implementing
the exact standard must be avoided if it cannot be ensured that
minimum performance levels are met when interoperating with all
other manufacturers' equipment meeting the standard. This standard
provides a means for measuring performance levels while trying to
ensure proper interoperation with other manufacturers'
equipment.

The issue of interoperation can only be definitively answered by
testing all combinations of encoder/decoder pairings. With the
number of equipment manufacturers expected to supply equipment,
this becomes a prohibitive task; therefore, the objective and
subjective tests rely upon the use of a "master codec". The master
codec is defined as the floating-point implementation of TIA-1016
[1] written in the C-programming language. The master codec
software, described in Sections 3.4 and 3.5, are used as part of
the interoperability testing. The master codec is available in an
associated Software Distribution as part of TIA-1016 [1].

By convention in this document, the Courier font is used to
indicate C-language and other software constructs, such as file and
variable names.

Additional information