I don’t really know much about the process of remixing a song but I can imagine it is a process that is like editing a video – layering tracks, adding beats, etc. They are clearly not doing that kind of editing live so they are basically playing something that’s already had some amount of that already done.
So what are they doing live besides maybe mixing between songs?
I just don’t understand what all the knob fiddling is about.
Yes, they are mostly mixing between songs. Doing that well and smoothly requires a certain degree of skill and experience. But the real skill of a DJ isn’t mixing, it’s song selection. Knowing exactly what song to play next based on the crowd and the flow of the set so far. Guys like Tiesto rose to fame in the 90’s/00’s based on their song selection ability rather than their technical mixing ability.
As for the knob fiddling, here’s a good firsthand overview: https://www.youtube.com/watch?v=nBlgwO8Fd-E&list=PL-IaIfDYdsAkuIDGKc78TP7aFI9kULp2N&index=3
In order to get a basic understanding, imagine a DJ standing in front of actual turntables. They start playing a song, and it has a downbeat (imagine if you’re bobbing your head to a groovy song, when you bob down, that’s the downbeat). As that song nears it’s end, the DJ doesn’t want dead air, so they choose a song that has the same beat. They put the record on the other turntable, and listen to it with their headphones. They listen and slow down/speed up the second song until the beat lines up perfectly, then fade the volume of the first song down while fading the second up. That way you’re listening to a new song, but the transition was so seamless, your head bobbing hasn’t stopped, or even been noticeably altered.
A skilled DJ can fade back and forth between two or more songs, do things like slip the hook from one song into the place where the hook would have been in a different song, and all sorts of other tomfoolery. The more sources of songs, samples, and sounds, the more knobs they need for volume, tempo and effects.
Then imagine someone mixing the sound for a live band. They have a slider for how loud the drums are in the house speakers, how loud the vocals are in the speakers playing back to the band. The DJ needs these too, so they can alter what they are hearing and what the house is hearing separately.
The music is composed of multiple elements each with their own instruments and sound. Some of them are looping elements to create rhythm and some are triggered manually to add highlight or voice to the music. When you are mixing a song you are adjusting the values between these different tracks, starting and stopping the tracks at the right points, modulating the tracks in various ways, etc. And when a DJ is performing he is doing this live in front of the audience. Even if he is performing an already finished piece he can still be a bit creative with it live on stage and follow the mood of the audience. Maybe it fits a bit better to extend one part of the track a bit more, maybe the timing of the dropp can be a bit sooner with the current audience, maybe the buildup can happen over a longer time, perhaps it would fit better to go back to another part of the track and improvise an ending instead of the planned ending since this audience responded better to the first part rather then the one used for the end, etc. They can change and modify whatever they need and create new elements or remove old ones as they see fit. Sometimes you even get to hear music that is yet to be released as it is a work in progress, the DJ might be trying it out for the audience to see how they respond. There is a lot of things which can be done differently in a live performance then a recorded one.
That being said it is fairly easy for a DJ to just put on a prepared playlist and just do nothing for the rest of the night. It can be hard for most of the audience to notice when this is done. And most DJs do play prerecorded tracks for part of the night so they can get some rest in between their performances, but the music can not stop.
Follow-up question: as someone who has enjoyed going to live concerts in other music genres, how does going to an EDM concert compare? Does seeing a DJ live substantially change or improve your appreciation for the artist? Do musical skill and personality shine through the same way it can for other musicians? Is the overall vibe closer to a rock concert or a big club?
The knobs could be panning between sounds or tracks, filter sweeps, adding or taking away frequencies in the eq, boasts to certain tracks, live looping, triggering parts of the song, depends a lot on the artist set up. A dj can be doing a lot with knob fiddles or just pretending they are doing something. Depends on the act