Attempting to get accurate SPL levels is the biggest mistake users of REW make! Do not fall in that trap. There is no useful information in there. Getting accurate levels is possible but requires extensive detective and configuration work with no net value. Get an SPL meter if you want to calibrate your system.
this can't be entirely accurate, misleading at best for new users, or perhaps i just fall into a specific subset of REW users
i use a PC --(USB)--> udac8 (bought before i saw the review on asr) --(RCA)--> icepower 500asp (2x500a) for LCR fixed gain and 2310ci for SUR volume set to -75 on the receiver and two iNuke NU3000DSP (knobs set to +15, no dsp processing)
my PC uses EqualizerAPO for all aspects of my tuning, as well as is my volume control
using my UMIK1, and my computer volume set to 52, which equates to -10dB in the udac8, i know exactly where i stand in the dB FS scale
that means when i play a -12dB FS test signal in REW, my TARGET output should be -22dB FS (-12 from the signal + -10 from the volume control) or 83dB as measured by REW (+/- for the respective house curves and such). Personally i measure at a nicer level with a -22db FS test signal for a 73dB target
after measurement, i have the possibility to read well over said target, in the EQ, i then set for my target DB, and the EQ pulls down all respective frequencies to match (no boost)
i now have an appropriate SPL level set on my setup
i will agree that those who have multiple volume/pots in their chain there is some additional setup that needs to be done
for instance, i used umik1 with pink noise set at -22dB FS and sent the signal to each SUR speaker, i then bumped up the volume knob until i was about +5dB hotter than my target, this way i knew there was enough head room, and the EQ would bring it down
for the iNukes, with no load hooked up, i ran a -0dB FS 100hz sine wave signal to it, and with the iNuke software i monitored each knob count until i began to clip the signal, then went two less than clipping. that ensured i was gain matched, and the EQ again would ensure my target level was matched
so i can't fully agree to this statement, while there is plenty to be done, encouraging folks to discard their SPL data can't be a good thing to do
