<font color='#000000'>I forgot the name of the disc, but there used to be a test disc that had a reference card with it.
On that disc you would go to the 20khz to 20hz sinze wave, and watch the time on the CD player. Once you find the spots where the sound is reasonably audible and where it stops being so, look at the card, and it had the frequencies that were covered in those spots.
I think the disc was 40-50 bucks if memory serves me right.</font>