This is a spin off thread of the "do you use a sub when mixing" poll I posted this morning. I thought it appropriate to mention and to discuss. This method of mixing was something my instructor used to talk about years ago; in that the key signature of a song could often determine resonant / fundamental frequencies in the mix - mostly in terms of them being "too much" - although I suppose it's entirely possible that they could be too shy at times as well. For example, let's say you're mixing a song in the key of A. It's more than just "probable" that the bass guitar will be hitting the fundamental frequency of 55 Hz throughout the song ( this is the frequency of an open A string on a 4 string bass, or the 5th fret of the G string). The octaves of that are 110 ( A on the G string) along with 220, 440, etc. But, the resonant center frequencies of those octaves can also come into play as well: for example, the related center frequency between 55Hz and its octave, 110, would be 82.5Hz. ( let's just call it "82".) So, knowing this, when mixing, do you ever pay attention to those resonant center frequencies on their respective instruments as well? It's food for thought, especially when you might have other instrumentation playing related frequencies and resonant center frequencies with (and possibly against) each other. In the key of A, the octaves would be 27.5, 55, 110, 220, 440, 880, etc. The possible resonant center frequencies of the above would be around 82, 124, 186, 280, etc. (I'm rounding off here again). And, we haven't yet taken into account the intervals of those notes - for example, the 5th to an A would be an E, so you could possibly have some harmonic overtones happening within the E's various resonant frequencies as well... Honestly, I don't mix too much with this in mind - it's pretty scientific, mostly I usually just use my ears and rely on what 'sounds good" to me, but... I do believe that it helps to know those notes and their related frequencies, if for nothing other than as being a good place to at least start at, when sculpting the EQ on a track, or when trying to tame certain frequencies that might be too resonant in a mix. Now, there are other variables too - I haven't included the possible harmonics that can be attributed to using certain input gain staging; like tubes, transformers; or tape saturation (or emulation), or even certain EQ's designed to emulate older classic analog pieces ( such as Pultec, SSL, Neve, etc.). No doubt it's a deep subject, deeper than I could ever really get into, but the basics of frequencies and related fundamentals is a valid point to consider, IMO. More info here: http://www.engineeringtoolbox.com/octave-bands-frequency-limits-d_1602.html and here: http://www.bass-guitar-info.com/FrequencySpectrum.html Anyway... just thought I'd bring it up as a talking point. Thoughts?