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G.729A
for the IP-II Phone Test System Microtronix
Systems Ltd. is now offering the G.729A Codec for the IP-II Phone
Test System.
The TIA-810-A standard, “Transmission Requirement for Narrowband Voice
over IP and Voice over PCM Digital Wireline Telephones”, states that tests
are to be performed using a G.711 codec. Telephone designers or manufactures
may want to perform additional testing on the telephone using a different
codec. The G.729A codec is one that is commonly available in VoIP telephones.
Since the G.729A codec has a much lower bit rate than the G.711 codec,
the test results may be affected. Care is required when making measurements
with high compression codecs. During our investigation of testing with
the G.729A codec, we found that different stimuli produce different results.
Microtronix
measured the Send and Receive Frequency Response and calculated the Loudness
Rating of a VoIP telephone. Figure 1 shows the differences in Loudness
Ratings for the G.711 and G.729A codecs with various stimuli.
All the test signals give similar results when used with the G.711
codec. With the G.729A codec, measurements made using Loudness Ratings
the different test signals varied. Frequency response measurements
made with a sine wave test signal exhibits variations in the response
at the lower frequencies, but the loudness ratings are very close
to the P.50 Artificial Voice. The Multi-Tone results were not repeatable
and the loudness rating results were too quiet with Pink Noise. Below
are example responses of G.711 and G.729A using Sine Wave (Figure
2 & 3) and P.50 Artificial Voice (Figure 4 & 5): |
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Test Signal
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Send
Loudness
Rating (SLR)
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Receive
Loudness
Rating (RLR)
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| G.711 |
G.729A |
G.711 |
G.729A |
| Sine Wave |
16.6 dB |
17.4 dB |
-12.7 dB |
-12.1 dB |
| Multi-Tone |
16.6 dB |
19.1 dB |
-12.7 dB |
-10.0 dB |
| Pink Noise |
16.6 dB |
20.4 dB |
-12.9 dB |
-9.3 dB |
P.50
Artificial
Voice
|
16.5 dB |
17.1 dB |
-12.6dB |
-12.1 dB |
Figure
1 Example Loudness Ratings
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Figure
2 G.711 Sine Wave Send Response
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Figure
3 G.729A Sine Wave Send Response
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Figure 4 G.711 P.50 Artificial Voice Send Response |
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Figure
5
G.729A P.50 Artificial Voice Send Response |
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Microtronix
recommends that those who wish to use the G.729A codec should use
the P.50 Artificial Voice, Real Voice or Sine Wave responses. However,
the test signal selection becomes an important issue with the increasing
complexity of IP phones.
Spectrum Analysis
The Spectrum Analysis software provides the ability to play an audio
file (e.g.: P.50 Artificial or Real Voice) through the Artificial
Mouth or to the telephone. Spectral analysis techniques applied to
the audio file and the measured signal allow the Test System to display
a frequency response.
Requirements
The G.729A Option requires the IP-II Phone Test System.
G.729A License
The customer must have a G.729 license from the patent holders. Microtronix
must obtain the customer name and address to allow us to enable the
feature in your IP-II Phone Test System.
Order Information
G.729A Codec Option: SW-G729A
(Includes G.729A Software Key and Custom Test Program)
Spectrum Analysis Key: SW-SPECTRUM
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Copyright © 1994-2004
Microtronix Systems Ltd.
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