MOH over cell phone

I have local MP3s as well as a streaming source and both sound GREAT over a POTS line or internally, yet over a cell phone the sound quality is horrible with static an chop. Im running Asterisk 1.6 and based on my research it seems to be the compression/decompression multiple times and the fact that cell phones are not made to play music, BUT… Has anybody had success with settings changes or anything to make it better? Everything else runs great but every time the office puts me on hold it bothers me since I’m the one in charge of fixing it! Thanks for any help!

It’s the vagaries of the cell system. Audio is highly compressed, bandwidth pinched. Frequency response is probably only in the range of 200-2500 HZ!


The default music that comes with FreePBX (I’ve never changed it) sounds ok on my mobile.

Do a test, calling your mobile from the office phone. Reject the call (or don’t answer) and start leaving yourself a voicemail. Put the call on hold for a while. Take it off hold and press keys to review the message. You should hear the music without cellular codecs and without any RF path impairments. If it’s still choppy, debug that first.

IMHO: Avoid streaming, unless the content is very predictable. Use an audio editor to prepare your music files. Start with instrumental content that does not depend on heavy bass or extreme highs, has a limited dynamic range, and doesn’t play too many notes at once. Filter it to remove what the mobile system can’t reproduce. To avoid artifacts caused by “brick wall” filtering, roll off e.g. from 300 to 250 Hz, and from 2500 to 3000 Hz. Convert to mono with a sample rate of 8 kHz. Adjust the level so peaks are about 10 dB below full scale. If it sounds ok on the computer, save the file in 16-bit wav format, upload it to your PBX and test on the cell phone. You may need to readjust the level and upload again.

That’s great advice on recording the MOH. One other thing that I would add is to compress it very hard. Dynamic range is also at a premium. I would compress it to the point that the loud vs. soft passages are with 3 db of each other.