Hey! Didn't I EQ that?

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Beaches077

Member
I know it's good practice to high pass basically every other sound in a mix so that it won't interfere with your bass sounds (Kick drum, Bass, Sub Bass). And, I also know that high passing the bass sounds is crucial for developing a clean and manageable lower end as well. Yet for some reason after I apply an EQ 8, for example, to the kick drum to carve out the super low frequencies when I look at the signal through Live's spectrum analyzer (or even another EQ 8 placed right after the initial one) I can still see those low, carved out frequencies in the signal. Albeit they are reduced they're still there. I use Ableton Live and I know that the program has some bugs/glitches and that very well may be responsible for the anomaly. However, if not a bug, what else could it be? Could it possibly be a by product of the algorithms used in Ableton's EQ 8? Should this be cause for concern?
 
Filters (and EQs) attenuate, they don't really cut stuff out outright. This is not buggy behaviour, it's math.
 
Steffo said:
But why isn't there an EQ that does cut out outright?
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I'm not so well versed with the math involved to actually explain it very well, but apparently the steeper the filter slope, the more "ringing" you get and the more f*cked up your phase gets. There are some plugins with really steep slopes, but haven't had the need to try them really...
 
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Right, the behavior of the EQ and ultimately it's signal processing capabilities boil down to how it was engineered (which algorithms it uses). My question now is: Could you run multiple instances of an EQ plug in order to further reduce unwanted sub frequencies? I know someone is going to ask: why not simply adjust the parameters on one EQ? If I were to attenuate the sub frequencies with an EQ by using a steep slope at the cut off frequency, could I then add another EQ that does the same thing to attenuate the signals even further? There seems to be situations in which you put an EQ either before or after a compressor. What if you attenuate the lows with an EQ, send the signal through a compressor and then place another EQ after the compressor to attenuate the same frequencies. Since the sub frequencies aren't completely gone the compressor will bring them up a bit so you would have to attenuate them again post compression. I've seen people debating whether to insert the EQ before or after the compressor. Wouldn't you always just use two EQs, one before and one after the compressor?
 
I don't think there's anything to "discuss", opinion-wise, about pre or post EQ - it's clear that they will produce different results and it's common practice to have first a corrective EQ, then your other fx, then an "artistic" EQ (which might slot in somewhere in the middle as well). But yeah, you can use multiple EQs if you want to. Stacking filters will steepen the slope, but I'm not entirely sure how the side effects behave when used like this.
 
There's multiband compression, and hardware-wise, there used to be something called a notch filter, which was a very surgical EQ (not saying there isn't a software version, but I've never seen one). You can try those, you can stack EQ's pre or post, you can use shelving EQ/high-pass/low-pass, but the reality is as krushing said-- you're not going to remove a frequency entirely, it's just not done. And if you could, you would be severely affecting the adjacent frequencies and causing yourself more trouble that would be harder to fix in the long-run.
Better to try and shape the sound at the source, whether through tweaking with a software or hardware synth, or mike choice and placement with a real recorded instrument or voice, as attenuating or enhancing the presence of those frequencies in your signal to begin with is preferable to trying to add or subtract with EQ.
 
rhythmgj said:
and hardware-wise, there used to be something called a notch filter, which was a very surgical EQ (not saying there isn't a software version, but I've never seen one)
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Really? I'm pretty sure almost every one of the modern freeform EQs (FabFilter's Pro Q or DMG's Equilibrium for example) include a notch mode...
 
See? I just never saw one (don't have either of those and don't work primarily in-the-box).
 
Beaches077 said:
My question now is: Could you run multiple instances of an EQ plug in order to further reduce unwanted sub frequencies?
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No. It's an inherent part of the way the filters work; the steeper the filtering, no matter how it's achieved, the more you end up boosting around the cutoff. I don't understand exactly why but you can't circumvent it.

You can use what's called a 'linear phase eq' which will let you get steep cutoffs without messing up your spectrum, but then you get a load of problems with transients which are imo worse- not to mention the fact that linear phase eqs use a lot more CPU than normal EQs

Another thing you can do is use bands rather than highpass/lowpass filters. This way you can make them very steep and you don't get any weird boosts around the cutoff.

My stance on it has always been that those tiny residual frequencies don't matter. Sure, you can see them, but you can't hear them much and they don't affect your mix in any noticable way. The spectral analyser can hear things a lot quieter than any human can
 
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You can fix this by not looking at an analyzer. I'm being half-sarcastic. Although an analyzer can serve its purpose as a learning tool you can't always take it at face value as a means to guide you as to what to do with your corrective tools. If something doesn't look right in the analyzer but it sounds right then it's probably right.

I think it serves as a great tool to see what the EQ is doing but I don't think it's a good idea to start putting in EQ's and filtering aggressively.
 
sleepy said:
You can fix this by not looking at an analyzer. I'm being half-sarcastic. Although an analyzer can serve its purpose as a learning tool you can't always take it at face value as a means to guide you as to what to do with your corrective tools. If something doesn't look right in the analyzer but it sounds right then it's probably right.
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Exactly - people have developed a whole new set of problems that only exist because they can see the spectrum; they process for the sake of getting the waveform to look nice and forget to listen :)

I'm not saying you shouldn't highpass & get rid of excessive bass, but there's no need to try and get rid of all of it.
 
I suspect an infinitely steep filter would require infinite processing power or create some infinite other effect like infinite phase distortion or something. Steeper filters usually mean more phase distortion.

Linear phase EQs introduce latency, presumably that latency increases as you make a steeper filter. I don't think it's a processing power issue, I think they are window based. You'd assume the window would getting bigger as the filter steepness increases (since zero steepness requires zero size window) which implies in infinite steepness phase linear filter would require an infinite latency.

Now that I think about it this could be why constructing a kick from multiple components is even more beneficial: you can keep the click part of the kick out of the EQ chain thereby keeping it's phase intact and precise.
 
^Yup, regular EQ plugins cause "phase smearing" because the part of the spectrum that's boosted or cut gets delayed a bit (because DSP always takes time) - linear phase EQs get around this simply (ok, probably not that simple) by delaying the whole signal so the phase stays intact.
 
I don't think it's really a CPU latency issue... it's from the maths. A LP filter takes a weighted average of the current and previous sample. The more of the previous sample you take the lower the cutoff frequency. I don't know how linear phase filters work but I assume they take a much bigger window ...use a furrier transform or something.
 
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If you really wanna get rid of lower or high frequences you need to use more then 1 EQ over and over again. But I dont see need to really get rid of the sounds ear cant hear.
Also, I think Izotope ozone can cut you frequences you desire.
 
It's also worth noting that those spectrum things are never accurate. They can give you high time precision or high frequency precision but not both. Short events will often appear as having a wide range of frequencies that don't really contribute much to the overall sound. Those extra frequencies might extend below the cut-off.
 
Thank you guys for sharing your knowledge with me on this matter. I didn't realize that it was standard practice to incorporate two EQs on a track with one being functional and the other being artistic. It's something that I'll have to start looking into. I tend to over-complicate things sometimes when producing or mixing music. The advice yall gave me will help to combat this tendency. Again, Thank you.

https://soundcloud.com/chazmblue/strangelights128final2017
 
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