Specifications

VoiceFinder VoIP Gateway Configuration Guide (APOS 2.0) Release Version 3.1
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of ADPCM voice quality.
z G.723.1 : This compression format is a part of the entire H.323 series standard which
stipulates a technique to compress the voice of multimedia service or other audio signaling
elements to a very low-bit speed. There are 2 different kinds of the bit speed in this coder,
which are 5.3Kbps and 6.3 Kbps. 6.3 Kbps of the bit speed is based on MP-MLP
technology and has an outstanding quality,. As 5.3Kbps is based on CELP technology, it
has a good quality and provides more flexibility to the system designer.
As codec becomes more and more dependant on the subjectively tuned compression techniques,
the quality measurement value-oriented standards, such as the total harmonic distortion or noise
rate against signaling, become less and less relative to the recognized quality of codec.
Therefore, the general bench mark, which is widely used in these days, to digitalize the
performance of the voice codec, is Mean Opinion Score (MOS). Voice quality and sound
quality is different from one audience to another and it is important to get a sample material and
wide range of audience. MOS is carried out by an audience group who ranks from the score 1
(the worst) to 5 (the best) for each voice sample
The table blow represents MOS score for the compression format used most often and required
Processing Power.
Compression
Formats
Bit Speed
(Kbps)
Processing
(MIPS)
Frame Size MOS Score
G.711PCM 64 0.34 0.125 4.1
G.729 CS-ACELP 8 20 10 3.92
G.729a CS-ACELP 8 10.5 10 3.7
G.723.1 MP-MLQ 6.3 16 30 3.9
G.723.1 ACELP 5.3 16 30 3.65
Table 3.1 Compression Formats and MOS Scores
As far as the maintenance cost for configuring the infrastructure, which is required to maintain
the general telephone quality level, is considered, it is effective to configure all the calls by
using a coder with a low bit speed. However, there are some disadvantages over compressing
voice repeatedly many times. As it is shown in Table 3.1, the one disadvantage is occurrence
of Tandem Encoding when coding and decoding is performed. As an example of compressing
voice many times by G.729 Coder, when encoding and decoding is performed 3 times, the
signal of MOS deteriorates its quality from 3.92 (very good) to 2.68 (not to be used normally).