Last weekend I played around with using the white-noise-like sound of applause in the hall as source material for more closely EQ matching the perceived response balance between four microphones in a recording array I'm using. I've long been aware that the particular way I have these microphones mounted affects their responses, making them less flat than their native measured response in free space, and in different ways for each pair. Beyond that, I'm not using a closely matched set of four microphones, so there are slight but perceivable frequency-response variations and somewhat larger sensitivity variations between each microphone to begin with.
Listening back and adjusting things later, I typically level balance and EQ by ear informed by memory, hunting for what sounds most natural and pleasing. I do so by soloing each channel and adjusting for anything egregious in isolation before checking as stereo pairs, then adjusting further as necessary with them all in use together. The later stages are an iterative process, and it is clearly apparent when the adjustments approach optimization- everything snaps into place in a natural and relaxed way and I find myself transported back to the time and place of the performance rather than noticing particular attributes of the reproduced sound which aren't quite right. This process improves not only the channel to channel level balance and overall timbrel balance but also the quality of imaging and the general impression of realism. The entire process ends up correcting for the particular response of each microphone itself, the response effects relating to how they are mounted, as well as the particulars of the music, musicians, instruments, room, etc.
This time I used the same process, but instead of level balancing and adjusting EQ while listening to the music itself, I did so while listening to the applause prior to and after the piece being performed, adjusting for naturalness and uniformity of applause timbre. This worked rather well, allowing me to more quickly get a good basic level and EQ balance between all channels so that when I switched to listening to the music itself the needed adjustments were already 80% there and I could more rapidly home-in on what was most natural sounding and correctly balanced.
I surmise this is due to a few attributes peculiar to recorded applause (perhaps classical applause stereo-typically, in that it seems to be more uniform, steady, and extended in time than the applause in other musical genera). Those attributes being: a relatively balanced, wide-spectrum source of noise; relatively even source distribution throughout the space so that it acts as a diffuse source; and a relatively even balance between impulse and steady-state noise components. I sat for a while considering the implications of seeking out highly diffuse noise environments in which to make recordings used specifically for calibration purposes, and what such a process would involve.
Here's the basic flow chart of what I'm doing now-
Raw recorded microphone outputs > channel balance and EQ corrections as necessary > corrected individual channel source material ready to be mixed/mastered
What I'm proposing is breaking down the middle correction part (in italics) into a couple separate sequential steps like this:
Raw microphone output > corrections for individual mic variation and their mounting > additional corrections as necessary > corrected individual channel source material ready to be mixed/mastered
Once determined, that first correction step can be reused for all recordings made through this setup until the microphones or the array in which they are mounted are changed. This thread relates specifically to that first correction step.