I was reading a technical white paper from Dolby outlining the proper way to monitor and mix 5.1 channel recordings in the studio. There is a fairly detailed section on calibrating levels in the studio...mostly stuff that is pretty familiar ground using pink noise and the Radio Shack SPL meter. But, when they got to the section on calibrating the sub, they said that the Radio Shack SPL meter is not really accurate using bandwidth limited pink noise for setting subwoofer levels. They recommended using 1/3 octave Real Time Analyzers instead. However, they stated that the Radio Shack SPL meter could give a reasonable approximation for setting sub levels if you adjust the sub level some 4 to 5 dB lower than the meter tells you to set it. In looking at some other materials, it appears this is indeed the case -- that the Radio Shack SPL reads 3 to 7 dB too low below 125 Hz. So, an indicated 75 dB on the meter is actually a subwoofer level up around 80 dB -- some five dB higher than it is supposed to be. I spent some time testing this "theory" in my own system tonight and I think it is definitely true. From my normal Avia calibrated sub levels, I backed off 4dB on the sub setting. On the wonderfully recorded DTS 5.1 Paul Simon in Paris concert DVD, the sound improved rather dramatically with the lower sub setting. Voices were much better, imaging was much better. I think that the sub had, indeed, been 3 or 4 dB too hot and that it was masking the midbass harmonics. The bass in the recording -- kick drums and superb electric bass -- was much improved. Interestingly enough, by turning the sub down, there was MORE apparent low bass extension ... again, I suspect because the excessive bass levels were screwing up the harmonics. Has anyone else played around with setting a good subwoofer 3 or 4 dB below what the Avia or Dolby pink noise test tones would indicate on the Radio Shack SPL? As a side note, if you want to hear mindblowing 5.1 channel sound from a concert, get this "Paul Simon in Concert" DVD recorded live in Paris in 2000. It has both DTS and Dolby Digital 5.1 channel soundtracks mixed by an outfit in LA called "5.1 Sound". These people clearly know what the heck they are doing because the mix is just astonishing. Perfect use of the center channel and surrounds -- the speakers completely disappear into one huge cohesive soundfield. I cannot believe that it is live recording (and from a big arena venue, no less) -- it sounds like a polished studio recording. It is a huge (and extremely tight) band -- three guitars, three drummers, horn section, two keyboards. There is a whole bunch of stuff happening at all times and you can pick out every note of every instrument. Amazing. The clarity and dynamic range of the recording is beyond anything you normally hear on a CD. The use of the 5.1 format on this one really shows how it is supposed to be done. No gimmicks, just unbelievable sound. This is the way music SHOULD be mixed. I've been listening to live records and videos since Live at Leeds and Get Yer Ya Ya's out 35 years ago. Somebody finally got one absolutely perfect.