Mid Range = Mud Range
Sound is energy. It requires energy in order to create sound, and sound waves can be harnessed to create energy. Low frequency waves contain more energy than high frequency waves. That’s why a subwoofer will often have a more powerful amplifier than the main speakers.
Because these lower frequencies contain more energy, as you blend multiple sounds together, the amount of energy in these frequencies accumulates unproportionally. Higher frequencies blend nicely together, but lower frequencies get muddy.
Another reason for the lower frequency mud is the physical shape of the waveform does not allow the possibility of adding very many similar waveforms.
Let’s go over this exercise for example, as I play a low note, and add another to it, Or as I play this note at 200hz, and add another 200hz note to it with a 10 ms delay. It just doesn’t work. Here’s what the waveform looks like. When adding these 2 nots together, you don’t get both notes, neither do you get either of the notes, what you do get is one messed up note that’s all muddy. This doesn’t really happen in the higher frequencies because higher frequencies are spread out more, therefore there’s less adding of similar frequencies.
As you can see, lower frequencies have less tolerance for being blended together than high frequencies. Within music, there’s usually not a lot going on below 100 hz, it should be just kick and bass in most songs, so we don’t have to worry too much about it getting muddy, however around 100 hz is where the bottom end of the frequency range is for human voice, and a lot of accompaniment instruments, such as guitar, piano... etc. So from 100hz up there’s all of a sudden multiple sounds and instruments being blended together, and it tends to get muddy, gradually clearing up as the frequency gets higher. For the purpose of drawing a line somewhere, I say it’s around 400 hz that it starts to clear up. So that’s why I consider 100-400 hz to be the mud range.
In the context of mixing a song, it’s pretty obvious that you are blending many tracks together, but I want to point out another source that causes mud, that is often overlooked. Room acoustics. As you saw previously, if I take. Note at 200 he, delay it by 20ms and blend it with itself, it sounds bad. If we delay it by the right amount, it can double up on itself, or cancel itself out. If we delay a different note by the same amount, it will behave differently.
Here’s a song with a graphic eq showing the peaks. Now I’ll play the same song, blended with itself on a 20 ms delay. You can hear it sounds wired. Let’s take a look at the EQ’s peaks, and we can see it has changed. Let’s do this example with white noise just to show it better. Now we can see the peaks going up and down. This is called comb filtering. this is exactly what happens in your room when the sound reflects off a wall. This affects both the recording, and what you hear from your speakers. It’s most prominent in the frequency range of 100-400 hz, and it contributes to the mud. But it’s never just a single reflection in a room. There’s multiple walls, floor, ceiling, and it will reflect from one wall to another, and then off another, and off another. So the sound being blended with itself multiple times creates muddiness.