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Q. How does knowing the key of a song help when mixing?

By Mike Senior

Some audio forums are really keen on pitch/frequency charts as an aid to mixing. I kind of get it: if a song is in A, you’ll have lots of 440Hz, 220Hz, 110Hz, 880Hz, and so on — but so what? What are you supposed to do with that information? And what about all the harmonics? And all the other notes in the key of A, and all their harmonics? So does knowing the key of a song actually help when mixing? Personally, I don’t think so, but I’d be happy to be corrected!

Jonathan Kaspar

If you need to do pitch–correction work while mixing, it can be handy to know which key you’re working in to reduce mistracking by the note–detection algorithm.If you need to do pitch–correction work while mixing, it can be handy to know which key you’re working in to reduce mistracking by the note–detection algorithm.SOS contributor Mike Senior replies: Broadly speaking I agree with you. On the face if it, knowing relationships between in–key pitches and specific Hertz figures might seem potentially useful if you wanted to pick out individual note fundamentals or harmonics for surgical EQ corrections, but those kinds of EQ moves aren’t that common in the normal run of things, in my experience. Even when you do need to find individual harmonics, I don’t think knowing the key makes it substantially easier — personally, I find it quicker to use a high–resolution spectrum analyser plug–in, such as Voxengo’s cross–platform freeware SPAN, because the relevant frequency peaks will usually be abundantly obvious to see (and measure) in the display. Alternatively, where I’m looking to boost a specific harmonic, it’s a piece of cake to just sweep a high–resonance peaking filter around in my EQ to find the frequency I’m looking for. Basically, I can’t see that knowing the key will really save you time in this regard.

However, when you need to apply pitch–correction to any part at mixdown, it’s often a lot quicker to set up the required correction scale if you already know the key of the music, and the same might also apply if you found yourself using any kind of intelligent harmony generator — to surreptitiously thicken backing vocals, for instance.

Another specific situation where it’s useful to know the exact relationship between musical pitches and frequency values in Hertz is if you’re trying to set up a short, high–resonance delay line as a pitched resonator — not exactly an effect you reach for every day, but it can be a surprisingly useful effect on occasion. In this case, you can work out the delay time you need by dividing 1000ms by the pitch’s frequency value in Hertz. So, for example, a 440Hz ‘A’ would require a delay time of around 2.27 milliseconds. Although it might be possible to sweep your delay time control around to find this value, the resolution available via your plug–in’s GUI may not make this very easy at such small delay times.

Published October 2014