TIA TIA-718-C

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This document specifies the procedures to test implementationsof EVRC-A, EVRC-B, or EVRC-WB compatible variable-rate speechcodecs either by meeting the bit-exact implementation, or meetingrecommended minimum performance requirements. The EVRC-A is theService Option 3 (SO 3) speech codec, the EVRC-B is the ServiceOption 68 (SO 68) speech codec, and the EVRC-WB is the ServiceOption 70 (SO 70) speech codec, all described in [1]. Theprocedures specified in this document for the SO 3 speech codec arefully consistent with those contained in [3]. The SO 3 speech codecis used to digitally encode the speech signal for transmission at avariable data rate of 8550, 4000, or 800 bps. The SO 68 speechcodec is used to digitally encode the speech signal fortransmission at a variable data rate of 8550, 4000, 2000, or 800bps. The SO 70 speech codec is used to digitally encode the speechsignal for transmission at a variable data rate of 8550, 4000, or800 bps.

Like some other speech coding standards, this standard providesa bit-exact method of verifying the test codec for minimumperformance. In this optional procedure, a given set of testvectors are input to the test codec and the output vectors from thetest codec must be bit-exact with the output vectors given in thesoftware distribution which is associated with this standard. Ifthey are bit-exact, the test codec passes the minimum performancerequirement and no further testing is required. The bit-exact modeof testing, however, is only applicable to codecs whose designconforms in all respects to the algorithmic description of thespecific EVRC service option, including the noise suppression, ratedetermination and post-filter components.

Should the candidate EVRC differ in any of these components, thetest codec shall be tested using the objective and subjective testsprescribed by this standard. That is, EVRC-compliance of a “testcodec” can be achieved by either:

• Complying with Sections 2.1.1 and 2.1.2 (SO 3), or Sections2.2.1 and 2.2.2 (SO 68), or Sections 2.3.1 and 2.3.2 (SO 70), anddemonstrating bit-exactness according to the procedure described inSection 3.1.4 (SO 3), or Section 3.2.4 (SO 68), or Section 3.3.4(SO 70), respectively.

• Following the objective and subjective testing procedures setforth in Sections 2.1.1 and 2.1.2, or Sections 2.2.1 and 2.2.2, orSections 2.3.1 and 2.3.2 of this standard.

With the exception of Sections 3.1.4, 3.2.4, and 3.3.4, theremaining text applies only to implementations that do not satisfythe requirement for bit-exactness.

Testing the codec is based on two classes of procedures:objective tests and subjective tests. In the event that the testcodec fails any of the objective or subjective tests, the testcodec fails the compliance test. Objective tests are based uponactual measurements from the speech codec function. Subjectivetests are based on listening tests to judge overall speech quality.The minimum subjective requirement for the test codec is based uponthe ability of the test codec to demonstrate performance equivalentto or better than that of the specific EVRC floating-pointbit-exact codec within a fixed allowable statistical error.

The purpose of the testing is not only to ensure adequateperformance between one manufacturer’s encoder and decoder but alsothat this level of performance is maintained with operation betweenany pairing of manufacturers’ encoders and decoders. Thisinteroperability issue is a serious one. Any variation inimplementing the exact standard must be avoided if it cannot beensured that minimum performance levels are met when interoperatingwith all other manufacturers’ equipment meeting the standard. Thisstandard provides a means for measuring performance levels whiletrying to ensure proper interoperation with other manufacturers’equipment.

The issue of interoperation can only be definitively answered bytesting all combinations of encoder/decoder pairings. With thenumber of equipment manufacturers expected to supply equipment,this becomes a prohibitive task; therefore, the objective andsubjective tests rely upon the use of a “master codec”. The mastercodec is defined as the floating-point implementation of specificEVRC written in the C programming language. The master codecsoftware which is described in Section 3.1.3 (SO 3), Section 3.2.3(SO 68), or Section 3.3.3 (SO 70) is used as part of theinteroperability testing.

Edition:

C

Published:

04/01/2008

Number of Pages:

146

File Size:

1 file , 550 KB