¯\(°_o)/¯ How the heck can a frequency cut cause clipping?

SimonTaddio_Qc

SimonTaddio_Qc

Headbanger
Feb 25, 2010
616
0
16
Quebec, Can
I was reading stuff on the internet about limiting and mastering, and came across this weird thing in the Waves L1 ultramaximizer manual, which can be found at:
http://www.waves.com/Manuals/Plugins/L1.pdf

This is straight from the manual
What is far less obvious is that applying an EQ cut also runs the risk of causing clipping. To prove this would take a
lot of math, but the following description should help get the point across.
At any instant, the peak level of a signal may be the result of several components at different frequencies and at
different phases relative to each other. Some components will add while others will subtract, but what happens if
you ‘EQ out’ a frequency that would otherwise be subtracting from the peak level by virtue of its phase? The peak is
now higher than it was.
Click to expand...

Ok, so I've done all my maths and all, and I know that substracting a negative number turns into a positive one, but...does someone can explain to me in what kind of situation this could happen?
They say in the manual that it rarely gives more than a 0.3 db boost, but that the effect can potentially/theorically be way more drastic than that.
So...anyone knew about this already? This is more curiosity than anything else, tho I find this subject real cool, lol.
 
I guess there is some truth to it. If you have two waves that are completely out of phase of each other. No sound will be heard. But if you eq one wave out, aka removing it, that other wave will start to be heard.
 
Pretty cool!


Think of two tones. Both have a peak frequency of 1khz. If they are pushed out of phase(either partially, or completely like Plankis said), there will be some destructive interference, and the overall volume will be lowered. If you then perform a cut of 1khz in one tone, there will be less destructive interference, and therefore, more overall volume.

I think that is the simplest example.







I think that is right anyway.
Its been a few semesters since Physics I :tickled:
 
you're correct, but this is not quite what they're talking about.

To understand this properly you have to stop thinking in the fourier transformed, frequency spectrum, eq display way about the signal and concentrate purely on the waveforms themselves

this isn't an ideal diagram but it might help:
FourierSeriesSquareWave_800.gif


imagine your signal was the black line. Now if you apply a low pass filter to that square wave, you'll get a signal that looks something like one of the coloured lines. As you can see, the peak level of the lowpassed signal is higher and could get clipped

edit: sorry, expected the diagram to have a background. I hope it's still readable

also, if you don't believe me then go try it with a square wave. The peak level will increase as you sweep the low pass lower and lower (until it starts to affect the fundamental, after which it will drop)

edit2: having said that you need to ignore the fourier transform, i then took a diagram from a page on the fourier series....oh well, the point still stands
 
It's been a while since I've done differencial/integral calculus and physics, but still I get the technicality of it.
But I wouldn't have thought of it this way by myself, but I'd have suspected more the phase thing, wich, you have to admit, is easier to understand as well :lol:

So all in all, if I get it correctly, cutting frequencies can boost your signal even on a single mono track, and it has nothing to do with the lowering of volume between 2 out of phase tracks, right?

Seriously, you guys are genius sometimes.
Cheers
 
The two things aren't really two separate issues. What comes out of your speaker is still one waveform, remember, (well two in stereo but ignore that for the time being, doesn't affect this) so whether this waveform is a single, mono square wave, or a combination of 8 tracks of various instruments, it's still a single waveform and still ultimately composed of sine waves. Phase interference between two guitar tracks and phase interference between the infinite sin waves making up a square wave is fundamentally the same thing.
 
I think you guys are making it more complicated than it really is. If the a low frequency is causing the peak, and you take it out, then you are dealing with the next highest peak, which the plugin may handle differently, and in fact cause it to clip.
 
Genius Gone Insane said:
I think you guys are making it more complicated than it really is. If the a low frequency is causing the peak, and you take it out, then you are dealing with the next highest peak, which the plugin may handle differently, and in fact cause it to clip.
Click to expand...

negative.

Read the OP again
 
kass said:
negative.

Read the OP again
Click to expand...

yeah, it's definitely not that. Clipping isn't something that only happens to the loudest frequency component of a signal. As a matter of fact, clipping of a complex signal is a nightmare to explain in the frequency domain, about the best you can do without serious mathematics (way beyond my understanding to explain) is go "it always introduces some higher order harmonics"
 
SimonTaddio_Qc said:
It's been a while since I've done differencial/integral calculus and physics, but still I get the technicality of it.
But I wouldn't have thought of it this way by myself, but I'd have suspected more the phase thing, wich, you have to admit, is easier to understand as well :lol:

So all in all, if I get it correctly, cutting frequencies can boost your signal even on a single mono track, and it has nothing to do with the lowering of volume between 2 out of phase tracks, right?

Seriously, you guys are genius sometimes.
Cheers
Click to expand...

it is to do with phase as well, the amount that the peak increases or decreases when you apply eq would depend heavily on the phases of the component frequencies.

also, boosting is the wrong word. If you make an eq cut, you'll definitely be reducing overall volume. You do have a chance of increasing *peak* volume though
 
John_C said:
yeah, it's definitely not that. Clipping isn't something that only happens to the loudest frequency component of a signal. As a matter of fact, clipping of a complex signal is a nightmare to explain in the frequency domain, about the best you can do without serious mathematics (way beyond my understanding to explain) is go "it always introduces some higher order harmonics"
Click to expand...

One way to sort of introduce the idea is that:

a.) A perfect square wave is made up of an infinite number of sine waves (every waveform possible can be deconstructed into sine waves - this is what happens when you look at a frequency spectrum analyser). It's hard to explain why on the internet but if someone really cares I can probably try.
b.) Therefore a partially square wave (i.e. a sine wave with the top half clipped off) must be made up of a far higher number of sine waves than the original (which in this case, was just 1), as it is characteristically similar to a square wave. The same thing applies to any waveform that has its top clipped off.

NB: this isn't aimed at you, as you clearly understand what's going on, more so at anybody else that's curious ahaha
 
i'm actually studying theoretical physics at university at the moment :p just coming up to 2nd year exams now. I did a module on fourier transforms a couple of months ago.

that page explains the sine wave summing -> square wave thing very nicely though, exactly what i was looking for as a demonstration.
 
waltz mastering said:
The increase in amplitude is caused by phase distortion above the shoulder frequency of the filter. Won't happen with linear phase eq.
Click to expand...

that's another effect entirely..... a completely genuine one but not actually the same

Hez said:
i'm actually studying theoretical physics at university at the moment :p just coming up to 2nd year exams now. I did a module on fourier transforms a couple of months ago.
Click to expand...

me too, although i'm just straight physics, not specifically theoretical :)
 
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