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Voice coders (vocoders) quality is usually measured according to a mean subjective estimation – MOS (Mean Opinion Score). MOS is usually calculated as expert estimations of a set of speech signals played by different phones. Each expert gives his score: 1 = bad, 2 = poor, 3 = clear, 4 = good, 5 = excellent. Mean value of the obtained results is taken afterwards.

CISCO Systems (www.cisco.com) gives test results for different codecs according to the clearest speech signal. Further down one can find CISCO test results compared to our automated audio codecs quality tests algorithms (ALG1, ALG2):

Table 1

Codec MOS ALG 1 ALG 2
G.711 4,1 99.38 98.85
G.723; 6,3 3,9 80.49 72.01
G.723; 5,3 3,65 74.56 60.80
G.726 3,85 82.49 78.45
G.728 3,61 71.96 55.76
G.729a 3,7 60.61 44.32
GSM6.10 3,7 72.46 55.38
G.729 3,92 83.4 90.2
AMR-NB 3,847 74 78.6

Table 2 represents mean values of ALG1 and ALG2 scaled down to values 1 – 5 (ALG values) compared to the same CISCO MOS estimations:

Table 2

Codec MOS ALG
G.711 4,1 4.96
G.723; 6,3 3,9 3.8
G.723; 5,3 3,65 3.38
G.726 3,85 4.02
G.728 3,61 3.19
G.729a 3,7 3.9
GSM6.10 3,7 3.2
G.729 3,92 4.17
AMR-NB 3,847 3.93

You can send us your inquiries on testing audio codecs developed by your company or yourself. If you are interested in audio codecs testing software, testing methods and other speech technologies developed by Sevana, please, contact us.

Vocoders Quality Checker

Please click here to download Sevana’s Vocoders Quality Checker demo. The program is a simplified implementation of Sevana’s solution for audio codec quality analyzer software. To start working with it please choose Tests -> Codec Quality. You will have three active buttons. Please push <…> button at Codec Library and choose one of the DLLs you have downloaded from our site beforehand:

“A-Law”
“G.723; 5,3”
“G.723; 6,3”
“GSM6.10”
“Mu-Law”
No “Codec”

which corresponds to voice codecs. Then press OK button. Button Cancel will bring you to the main program window.

After you pushed OK button, the program loads DLL and checks its interface. If the interface is ok, then the following process starts:

  • program requests codec’s frame size and generates a test set of audio data according to the proper frame size;
  • correspondent vocoder is loaded from the DLL and program passes the audio signal array together with all parameters into it;
  • vocoder starts encoding;
  • original and decoded signal are compared using internal audio signal comparison function;
  • window with signal similarity coefficient is displayed. 100% corresponds to identical signals.

Are you interested in testing your own vocoder? It’s no problem doing that even in the demo version of Sevana Vocoder Quality Checker! Please go to Tools -> Generate DLL Header, choose a desired file name and press OK. Include the DLL header file into your project and provide two DLL functions according to the DLL header file. Thus, by implementing your own vocoder as a DLL file you will be able to test its quality using our software. Unfortunately demo version does not allow you comparing two audio files, but this feature is available in the full version of the Sevana Vocoders Quality Checker.

If you have any questions, interested in full version of the Vocoders Quality Checker, or would like to have it integrated into your software please contact us for further information.

The PAD file is available also.

 

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