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Default systems files are delivered in the GSM format. In order to improve the quality, you must source all those files and replace them. There are two types of sounds: 1) Prompts Default prompts come in all needed formats (ulaw, alaw, gsm, g729) to avoid transcoding. (Look under System -> Sounds to change the format) The quality of these sound files is easy to test: Make an extension and force its codecs to 'gsm'. Dial *123 and browse the prompts. Now edit the extension and force codec 'ulaw' or 'alaw' (disable all other codecs). Dial *123 and you will notice the difference. This should be done with a standard hardphone (such as Polycom) rather than a softphone on a PC. If you want to upload a new prompt/greeting, you should use the 'Sound Converter Wizard' which will convert a high quality WAV to a set of native formats in the PBX. There is only one case in which the prompt is only 'gsm' and that is when you create it with the phone (but that will be of poor quality anyway). 2) Music on Hold Music on Hold can use MP3, but we strongly advise not to. Even though we do not use an external process (such as mpg123, aplayer, etc) to transcode MP3, we have had numerous crashes on high-load call-center systems. We decided to create a tool which will be a front-end for the best Open Source tools available on the market and will convert the MP3 to native formats. Such a tool for the MP3 format is 'lame' (there is no better encoder/decoder than lame) and the 'WAV' produced by 'lame' is converted to native formats with 'sox' (there is no better tool for the job). Such music can be easily tested by dialing *388. The highest quality will be if you use either 'ulaw' or 'alaw' codec. You must test 1 and 2 locally and sound should be good. If you have problems dialing through a provider, that is a separate issue. We had a problem in the past where the client was using a provider with Silence Suppression and the quality of MoH was low. There is no need to search for other ‘converters’ because the Sound Converter is enough.
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