What’s the roll-off of that slope?
“Roll-off this sound, but watch the slope” – you don’t hear this kind of advice all that often. Certainly not, when it comes to mixing, mastering. Or music in general. Maybe it’s too technical for most people. And the good artists, with great ears don’t need it. I mean, they don’t need to know the technical details. They can achieve it with simply listening to the whole thing. And sometimes it’s not really a control thing. Sometimes you just have to accept that this or that has a certain roll-off curve. Are you confused yet? Just bear with me, it’s nothing mysterious.
Rolling shit off – it’s fun
You may have heard about the Izotope Ozone mastering plugin, or happen to have it. It’s got two guide lines in their spectrum analyzer. The -3dB and the -6dB guides. It means the fall of these lines are -3dB and -6dB per octave. These are good visual guide lines for what you need to approach with the sound. Why? Because sounds with a curve like these tend to sound natural and pleasant to our ears. I could say all the silly things like “warm”, “phat” or “punchy”, but I’ll refrain from that. In (audio) physics, there are noises with certain colors. Pink noise happens to have a -3dB per octave drop. It sounds pretty much like waterfalls, or ocean waves. There’s also a red- or Brownian noise with a -6dB per octave roll-off. It sounds like a somewhat muted waterfalls. Or ocean waves. Listened from a distance. You get the idea. Interestingly, an acoustic guitar has a frequency fall-off pretty close to a perfect -6dB per octave one. Generally. No wonder it works so good as an accompaniment. Or a one person band.
Getting the natural curve
Anyway, when we have a complete and complex music with many different instruments, some kind of random thing happens to the frequencies. Not unlike the random movements in the Brownian particle theory. Hence the similarity in their roll-offs. Use such guidelines cautiously though. Even if they provide great visual help, you shouldn’t rely on it without doing it the hard way. That’s using your ears. And your brain power. Why the cautiousness? Well, imagine a song that doesn’t have hi-hats. Or shakers. Or tambourines. Or an acoustic guitar. And really, nothing that can provide those truly high, “air” frequencies. Now you start mixing and mastering the tune. You’ll sweat monkey pee while trying everything. Just to pull up that top end, to match the fukken guide line. You end up adding a lot of hissing noise. Yet the meeting of the two just ain’t ever gonna happen. The bottom line? Screw the slopes and use your ears, b00v.