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):


Test Signal

 

 Send Loudness
Rating (SLR)
 Receive Loudness
Rating (RLR)
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
Figure 2 G.711 Sine Wave Send Response Figure 3 G.729A Sine Wave Send Response
Figure 4 G.711 P.50 Artificial Voice Send Response Figure 5 G.729A P.50 Artificial Voice Send Response

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