I'm using SpectraLab, but unfortunately, this is a commercial package and it costs money (or you can just use the free trial version)...I haven't found any freeware programs, but I'm sure they exist...maybe not. :-) I'm using the Radio Shack analog SPL meter which has an RCA output, going into the line-in jack on my laptop. Unfortunately, the signal-to-noise ratio is horrendous, and I'm only getting maybe 20dB of headroom above the noise floor...however, this solution is more accurate than just using your ears.

As far as whether or not you want a perfectly flat freq vs. amplitude, that's up to you...ideally, we'd match the freq response of the studio recording/mixing equipment, but different studios use different setups... perhaps some of you are capable of adjusting your eq's to compensate for aberrations that you hear...I am not. I can tell generally what range needs to be boost/cut, but the exact frequency range is difficult to pinpoint. This frustrated me so badly that I finally got a makeshift RTA system setup - in general, my adjustments were on the right track, but I could never match the improvement in SQ that I could using the RTA. In reality, I wasn't calibrating my car system to a flat response, but rather, to a home system that I know sounds good.

But the bottom line is that if whatever you have sounds good to you, then don't worry about it. NONE of my friends can tell the difference between a high-end setup and a mediocre setup, although they can "feel" differences in bass...maybe. If you're not anal retentive about sound reproduction (like me), then I say just enjoy the music. :-)

Valsalva