Ok. I know you didn't want feedback on the mic, but I waited all day patiently until answers were provided, and being someone who records vocals and mixes tracks, I'm going to speak.

I understand what you're trying to do, but as you may know, you'd be better off with a dB sound sensor module along with an ADC (Analog to Digital Converter), you can get this working very reliably with pretty accurate results on a Raspberry Pi. If you use an Arduino board, it has no problem with analog signals, so you don't need the ADC (but then, you wouldn't be able to use Perl...).

Because it would connect to the GPIO (SPI) and not via USB, you'd need a Perl library that can manage that. A search through the CPAN should turn up a few libraries to at least get started.

This info isn't here to chastise. It's here in case anyone in the future that is using Perl wants to do the same thing you want to do.

disclaimer: I've never done this with my Pi (I know others who have though), but I have several ADCs, so I think I'm going to test this out to satisfy my own curiosity.