Customizing ring tone for console/dsp?

I have set up a custom console/dsp extension for an overhead paging/ringer system.

It works well, except for one thing: the ringer sound is extraordinarily annoying. I have searched and searched, looking for a way to customize the ring tone, which is either generated or played by the server, since that is where the extension resides (in other words, it’s not sending a “ring” command to an external phone…it is the phone itself, and sending the audio to the speakers).

Does anyone know from where these sounds come? I looked at indications.conf, but that seems to be for the handset ringer sound that is played to a caller.