How-To: Simulate the sound of a telephone line

To make the caller sound like they were on a phone you can do one of two things:

1. Record the audio from the other end of a phone call.
2. Record it normally and then post-process it.

Option 1 is ok, so long as you have a good way to record from a phone. If you have a phone with a headphone port then you can plug into that and record.

Option 2 is more flexible, letting you easily add background effects, and will give you a better quality sound with more control over the final output. You can also do it live if you have a suitable graphic equalizer.

A standard phone line carries sound in the 300Hz to 3400kHz range, which is sufficient for the human voice. It is the cutoff at both ends that gives a phone-call its distinctive sound (not the phone itself), removing the high and low frequencies from the voice of the caller.

So, to simulate a phone line, just apply a frequency filter (in software or using a graphic EQ), setting all the frequencies below 300Hz and above 3400kHz to zero. If the effect is too strong then you can tweak these levels.

That is probably good enough for a live performance, remember we still want the audience to understand the caller. If you want to add more realism, add a slight echo before you apply the filter, or a subtle bed of white noise to make the line sound a bit rough.

I have also found that applying an audio compressor (again in software) can add to the effect by flattening the voice further. This can also make it easier to set a level for live playback, as there is no volume fluctuation during the “call”.