OBi1032 Voice Quality Lower than OBi202
SteveInWA:
Geoff, what's your analysis of the issue?
Charlemagne:
Thank you both for your responses. I appreciate the additional information on the 1032, and will be interested in hearing the clarity of the Opus to Opus connection.
Since my original post, I have bypassed the Voice VLAN switch entirely, connecting directly to an unoccupied router port, pointing Voice VLAN traffic there as well. I also did a factory reset of the 1032, configuring only SP1 with GV, with no other SPs present. In both instances, Call Status still reported deficiencies, e.g., MOS-LQ 4.09 / Packet Loss Rate 1.27 (with that number declining during the progress of a 5 to 10 minute call to maybe 4.34 / 0.25%. Tolerable perhaps, but not something I'd want to subject a conversation to, if I could avoid it.
I haven't limited my efforts to self-testing. I've also called out and received calls from others. They can hear on their end of the conversation the voice quality issues I observe concurrently on the Call Status page. So, I find a reasonable correlation between the Call Status statistics and the voice quality perceptions.
So, I am back fundamentally to where I started, but a little more knowledgable.
Any further thoughts or ideas would be most welcomed.
SteveInWA:
Go do some research on MOS. The term refers to a "Mean Opinion Score", which was a method developed during the old Bell System days, well before VoIP and computer testing. A panel of actual human listeners was used to listen to the sound quality of phone calls. Much like the Olympic ice skating judges, each panelist would give their subjective opinion of the call quality, and then those scores would be averaged. It is difficult to get above 4.0 on the PSTN; calls at MOS 4.0 or higher are considered good audio quality.
MOS calculated by algorithms may not represent nor agree with human opinions. The ITU specifically includes a statement that MOS results may vary from one experiment to the next.
See: https://en.wikipedia.org/wiki/Mean_opinion_score
Bottom line: a) I have no idea what is causing your particular observation, and b) there are several audio parameters that can influence your perception of audio quality, most notably amplifier gain/overdrive/clipping. If you believe that your OBi IP phone is defective, get it replaced.
Charlemagne:
Thanks you. I provided the MOS info not because it's conclusive or because I'm relying on it in substitution of my own judgment, but because OBi selected it for inclusion, presumably as a standardized measurement, and as a reported variable to assist in analysis. The Packet Loss Rate provided may be a more direct indicator. Perhaps not coincidentally, when the Call Status readings are better (including among others, the subjective MOS, the Packet Loss Rate, etc.), the voice quality is better too. The noticeable voice quality issue, observed by me and those with whom I speak by phone, naturally preceded my effort to quantify the deviations relative to the OBi202's higher quality - using those tools which OBi provides to end users.
I will try TX and RX levels too. My experience with altering the defaults (on the 202) has not be particularly productive.
You may be right that mine is simply a defective unit. Of course, under the circumstances it's difficult to know in advance whether replacing it would indeed solve the problem.
Thanks again for your help.
SteveInWA:
Incidentally, I should have mentioned:
The theoretical maximum MOS for the G.711 CODECs is 4.4. Anything in the range from 4.0 to 4.3 is considered a "satisfied listener" score.
RE: experimenting, if you have a friend who is patient and has as much time as you to work with test calls, the first thing to figure out is whether the perceived call quality is poor when you are the listener on your end, or if the person on the other end is listening and evaluating. If their voice sounds good to you, but your voice sounds bad to them, then fiddle with the microphone gain settings. There is a narrow range between the level being too soft, and being overdriven/distorted/clipped. If it sounds bad on your side, and you have tried a few volume settings, then it's probably some other issue.
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