MOH Distortion on Cell Calls 2

[hawkflorida]

This problem has to do with MOH distortion on cell phone calls. The units are MICS and CP. When a cell user calls into MICS the AA picks up all the recordings are fine. When the caller is put on hold there is an extreme distortion of the music. Multiple cell provider calls have been made with the same results. Land line calls have no distortion on MOH. When this site had a non-Nortel KSU there was no distortion on MOH. Any ideas would be appreciated. I apologize for not having the SW levels or type of MOH source yet. I will get those details ASAP. Thanks for any ideas you may have....

Consulting -
If You're Not A Part Of The Solution, There's Good Money To Be Made In Prolonging The Problem.

 

[norstarboy125]

If you press f86 from a set is the music clear...

 

[misseditbythatmuch]

I am still learning about this, so the best I can offer now is this experience.

An 824 I support with Flash vm had the same symptoms when MOH was recently added.

After talking to different support folks, I got the following explanation, and here it is in a nut shell.

Cellphones are using codecs that are increasingly bandwith sensitive and convert audio analog signals to digital in a compressed format generally ranging from 13k to 8k and pushing ever smaller to conserve bandwith. The upshot is that the algorithms for the codecs are getting more and more fussy with what is rejected as non-voice signal. Music on hold that deviates from the range of conventional voice range frequency and saturations is increasingly rejected or processed as "noise."

8 and 600 ohm sources are weak to start with and contain significant noise (some inaudiable, some audible) this adds to the amount of rejected sound samples. Some samples will be suppressed by the codecs and treated as if they were background noise. End result is choppy sound with volume swings. So, when it meets a cell station to be encoded, the codec rips out the perceived "noise" and mutes the background noise and leaves a "moth-eaten" soundtrack for the recipient.

A copper land-line caller, when put on hold, was directly switched to the analog source, and the signal was unfiltered by any codecs. This allowed for a "good" sounding MOH.

I did some testing and found that if I used MOH that relied on very simple vocals, I had very little loss to cellphone callers. When I used instrumentals, especially classical music, most the the accoustic range was trimmed off by the codecs.

As for your experience, with a non-Nortel system not creating the drops/choppiness, I do not know why different. However, a few years ago the cell phone codecs allowed more bandwidth so that may have helped it. If it was more than a few years back, you may also have been working with analog cellphones, so no codecs. Also, if the other system used any hardware settings to clean up the source, it may have encoded better. It may also be that the actual music was closer to conversation that what you have now.

As a test, try a conversation level MOH source. (I used a CD with classic Military Cadences). You could even hook up a cassette player and a book-on-tape reading as a test signal. Does that sound better over cell phones ? In my case, it made a noticeable difference.

I realize this is not diagnosis of your system problem, but it may help provide some more data to frame the discussion.

 

[hawkflorida]

Thanks for the information misseditbythatmuch . That was quite helpful.

Consulting -
If You're Not A Part Of The Solution, There's Good Money To Be Made In Prolonging The Problem.

 

[SupportDude]

To simplify that answer ...
Don't complain when you're calling on a cell phone.

For crying out loud ... You're calling from your car, a park, the golf course, your girlfriends house, the parking lot, the bar, etc., etc.!!!! What the heck do you want?

Just the fact that it works should tickle you to the point that you wet yourself!

Sorry ... I grew up in the age where color TV's and 8 track players were a big deal.

-SD-

http://www.mysupportguy.net

 

[hawkflorida]

Support Dude... I totally agree on cell phone expectations and offer those same sentiments often enough myself. The explanation researched by misseditbythatmuch answered the question perfectly. I too remember the "good old days" but when a KSU is changed out with another product line and then suddenly shows a problem some sort of explanation is in order. This customer is now using Classical Music for their MOH source. I'll suggest a change. Thanks for your .02 worth though. Every "little" bit helps.

Consulting -
If You're Not A Part Of The Solution, There's Good Money To Be Made In Prolonging The Problem.

 

[SupportDude]

LOL ... sorry about the rant and I totally understand you position as we've all been there ... and what you really want to say is, "Well, this isn't your old system!".

I found the info provided by misseditbythatmuch educational and informative myself.

Thanks misseditbythatmuch!

-SD-

http://www.mysupportguy.net