Aha! Found some help on the Mitel switch page - It suggests using Cooledit 2000 and gives the following instructions -

Click Transform, click Amplitude, and then click Amplify.

After the Amplify window opens, click the 'View All Settings in db' check box. Click the Constant Amplification tab and type -15 in the 'dB' text field.

So.

It is indeed -15 (Although in truth the instruction was split with the '-' on one line and the 15 on the next so it wasn't easy to spot. That's my excuse anyway:-) )

Them were words of more than one syllybub, Bernard! But I think I'm begining to get the picture. On WavePad it gives percentages so If I take it to, for instance, 25%, of the original how many dBs would I be reducing it then? Or is it not that easy?

It may take me a while but I'll get there eventualy...

:D