This exceptionally affordable device only switches between inputs.
You'll still have to do volume matching the same as you would if you didn't have a handy little switch box.
I use a free iPhone app SPL meter by JL Audio, in combination with a lapel mic that I place between the ear pads while the headphones are resting on the desktop, undisturbed. I play a white noise WAV file first through one chain, adjusting the volume to 85.0 dB, then through the other chain, again adjusting the volume to 85.0 dB.
Leaving the volume control(s) where it (they) need to be for each chain, I'm ready to make comparisons - with the headphones on my head.
Edited by zilch0md - 5/5/13 at 6:51pm