TIA-127-E:2012

Service Options 3, 68, 70, 73 and 77 provide two-way voice
communications between the base station and the mobile station
using the dynamically variable data rate speech codec algorithm
described in this standard. The transmitting speech codec takes
voice samples and generates an encoded speech packet for every
Traffic Channel frame.† The receiving station generates a speech
packet from every Traffic Channel frame and supplies it to the
speech codec for decoding into voice samples.

Speech codecs communicate at one of four rates corresponding to
the 9600 bps, 4800 bps, 2400 bps, and 1200 bps frame rates.
However, Service Options 3 and 70 do not use 2400 bps frame
rate.

The specifications defined in Sections 4 and 5 of this document
provide the detailed algorithmic description of the EVRC. In the
case of a discrepancy between the floating point and algorithmic
descriptions, the reference floating point c-code will prevail. The
specifications defined in Input Signal Preprocessing (see 4.4),
Determining the Data Rate (see 4.8), and Adaptive Postfilter (see
5.9 and 5.10) are optional for implementations intended for varying
operational environments (such as in-vehicle hands-free). Any
implementations which deviate from the algorithms specified in this
standard, shall meet the minimum performance requirements defined
in the associated Minimum Performance Specifications.

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