I think some good points have been raised here. Mixing in key can be more or less important dependent on the kind of music you play. For instance, if you play really minimal music that is mostly rhythmical with very little tone, there is far less propensity for clashing between tracks, however, If the kind of music you play has any tonal elements or progression to it (which i personally consider to be nearly everything, even drum sounds play back with prevalent frequencies which ultimately equal tone), then mixing in key is absolutely essential.
I always equate this to the idea of going to see a band perform. If the guitarist played all the songs in one key, and the singer sang them a semitone out, and the bassist played them another three semitones up from that, it would sound like a hideous mess and most likely a lot of people would think ‘This sounds like shit, i’m not sticking around to listen to it.’ Even if you have little to no intrinsic understanding of harmonic relation, most people can just instinctively feel when something sounds clashing. With that in mind it has always puzzled me that generally DJ’s don’t seem to be held to a similar kind of standard. I understand that a DJ should be lauded for lots of reasons, like their track selection and ability to read the crowd and so forth, but it still seems like quite a rarity that people are really given credit for finding songs that work so well together that it sounds like they could have been made as one thing.
Someone also mentioned that it’s less common for people to think about conflicting drum grooves. This is so on point. Two clashing grooves can completely strip the energy out of what’s going on, even if the two tracks sound great harmonically…
There have been plenty of discussions regarding key detection software, but my two pence on it is this. If you can learn to (or naturally) do this by ear, it is the single most effective way of doing it, and a worthwhile endeavor if you’re serious about the concept. No key detection software is infallible, because it is not actually ‘listening’ to the music, it’s just analyzing the prevalent frequencies in a waveform, and that in no way means that those frequencies have to equate to the root note of the track (ie: the key). They will most likely form part of the major or minor chord of that key, for instance, a track in C minor/major could have a lot of these notes in it: C - D Flat - E - G, and if the software picks up on any of those occurring frequently, it might label the track as that note being the root key of the track. So, while it might have a harmonic relation to the actual root key, you’re going to start mixing between tracks with essentially inaccurate information. Mixed in Key gets so much love, but i think that it’s not all it’s cracked up to be. It will label things as a fifth out from its actual key (as per what i mentioned above) too much to really be considered accurate. If it labels 5A as being 6A then thats fine when you mix 5 to 5 or 5 to 6, but if you try to mix 6 to 7 (which would be permissible under the theoretical concept) and the reality is that you’re actually mixing 5 to 7 then the likelihood is that the mix won’t sound very good… MIK are so precious about nobody stealing their ‘special’ algorithm that they make you connect to the internet to use their product, which i think is quite a big ask on the part of the consumer. It would be more deserved if their software wasn’t so frequently inaccurate. Also, modulating key by 5ths is not the only way to move around keys. Mixes with other intervals such as 3rds and 7ths can also sound pleasing (although they’ll almost never follow progressions together), and can help stop you from being slaved to playing a track just because the key is right, and not necessarily picking the right tunes for the moment. Invariably though, tracks with little to no tonal content in their intro/outro are the best way of modulating from one key to another…
The one good thing i will say about MIK is that the system of replacing keys with number values is actually quite handy. Especially if you’re looking down a list of a lot of tracks. Picking out a number at speed is far quicker than picking out a letter and then potentially a flat or a sharp symbol, especially as the number sticks out starkly from the letters of the track name/artist. If you do need to pick a key detection software, from the results i’ve seen i’ve found rekordbox to be more accurate than MIK. I’ve not tried keyfinder, so can’t make any comment as to it’s accuracy.
Lastly (and as a shameless plug) If you’re interested in the concept of harmonic mixing or want examples of it, it’s worth checking this out. It’s just under 3 hours and 166 tracks worth of harmonic eargasming goodness.
https://soundcloud.com/stereotypemashup/songs-in-the-key-of-fuck-yeah
Thanks for reading my diatribe/essay/novella…
I just wanted to talk … ??