[Speex-dev] PESQ calculated MoS-Values for Speex

Oliver Martin scholl3ss93 at gmail.com
Wed Jan 9 04:00:28 PST 2013


I just signed up to this mailing-list (note: my first mailing list at all),
because I'm having some problems related to speex.
Let me just introduce you to what I'm doing.

I am writing a short (really short) paper about VoIP techniques, especially
audio codecs for speech.
I pointed out basic technologies behind audio codecs; vector quantization,
lpc, long-term prediction and some more.

I planned to compare G711(.1 eventually) and speex with reference to
(which is a bit weird, since the encoded g711-files are 6 times larger than
the original wave files - but this is another matter), MoS value,
and a subjective opinion, wether I can still understand the file, or not.
The MoS value is (or rather *should be*) calculated by PESQ (ITU P.862:
(I know the pesq scale ranges from -0,5 - 4,5, where MoS is usually from 0
- 5)

*Pesq Settings:*
R2a: Sampling Rate: 8kHz, Overall bit rate: 80kbit/s
R3: Sampling Rate: 16kHz, Overall bit rate: 96kbit/s

*Pesq Results:*
R2a (mode 2) of G711 returned Mos-Values from *0.656* to *3.33* (parameter
+8000 in pesq)
R3 (mode 4) of G711 returned Mos-Values from *3.981* to *4.269* (parameter
+16000 in pesq)

*Speex Settings:*
To get comparable results I decided to use settings that conform with the
G711 ones. Command-Line Parameters:
"mode 2": "-n --comp 10 --quality 10 --bitrate 80000"
"mode 4": "-w --comp 10 --quality 10 --bitrate 96000"

*Speex Results (this is where it starts to be weird):*
mode 2: Mos Values from *2.541* to *3.211* (parameter +8000 in pesq)
mode 4: Mos Values from *2.045* to *3.355* (parameter +16000 in pesq)

I tried to get better values, at least in mode4, for like 2 hours, but I
did not get something that corresponds to this:
http://speex.org/comparison/nb_codecs_small.png (Speex.org Website).
The fact, that a bitrate of like 25kbit/s results in a score of nearly 4,5
is confusing me like hell. (compared to my results)

First thing I tried was just "speexenc origfile.wav destfile.spx", but the
result did not satisfy me.

The used wavefiles are created in Cubase5.1, 16bit and 16kHz.
Im using 1.2rc1, compiled with cygwin, running on Windows 8.
The 1.2beta3 kept crashing on Win8 and Win7 using the same audiofiles.
I also tried using 1.0.5, but the (MoS)results were not satisfying.

I have no clue why the score is at such a low level (compared to the
graphic below).

Let me already thank you for your help.


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