﻿Hi and welcome back,
I’ve seen a fair bit of discussion about EQ cramping recently; partly in response
to my bx_console Amek review, in which, spoiler alert, I discover that the high mid band cramps,
even though the high band doesn't… and partly due to a recent White Sea Studio video about the
SSL EQ plugin, under which every other comment seems to be recommending my ReaEQ video.
So I thought this might be a good time to make a short video just about cramping:
what it is, and perhaps, how its commonly corrected, so you don’t have to watch an hour
long review of an unrelated plugin. Ok, here’s a 10k boost in Pro-Q3.
Notice how nice and symmetrical it looks. Thats how its supposed to look.
Ok, now here’s ReaEQ, also doing 9dB of boost at 10k,
and I’ve tweaked the bandwidth to match the width of the bell as best I can.
But notice that I can only get anywhere close to matching the lower half
of the bell… I can get that pretty close… but I can’t match the upper half at all,
because regardless of the bandwidth setting ReaEQ always plunges down to unity at Nyquist.
That gives us an asymmetric bell shape, and also significantly less of the airy
frequencies between 10 and 20k. This is cramping, and its a consequence
of using the bi linear transform to derive the digital version of an analogue filter.
Or to put that another way, its a problem with the basic underlying maths that underpins digital
filters, rather than any specific implementation. All analogue style digital filters will do this
unless you take steps to correct it. There’s more than one way to fix this problem. You
could use a higher samplerate for your project, or the EQ plugin could oversample internally:
this will move the Nyquist limit higher, and significantly reduce the cramping.
If I switch the analyser samplerate to 192KHz… the curves match much better… at least,
once I’ve adjusted ReaEQ again. But oversampling is a bit of a brute force
approach, with several potential downsides including latency and higher cpu use.
Is there a simpler way? Lets turn off this band in ReaEQ…
and replace it with this one… its exactly the same but with less gain, to compensate for the fact
that I’m about to add a high shelf… and suddenly the two curves look a lot more alike.
If I switch to show the phase response… its also very similar…
Now granted, they’re not identical, but there are a lot of variables to tweak:
the frequency of the high shelf, the way the gain is split between the two bands,
the bandwidth; I can’t be bothered to try to tweak all those to perfection if I’m honest.
But it wouldn’t surprise me if, given enough time and patience, I succeeded
in nulling these two bands of ReaEQ against a single band of Pro-Q3 in zero latency mode.
Now that will all change if I switch to Natural Phase mode…
because natural phase mode fixes the phase response in the high end.
Pro-Q3 now gives us a nice symmetrical phase response as well, at least until we get
comfortably above 20KHz, where it inevitably has to return to zero because reasons.
Whereas ReaEQs phase response is shifted upwards: if we turn off Pro-Q3… we can see that at 10k,
the frequency we’re actually targeting, this should be at zero phase,
but it isn’t, its shifted upwards slightly because of that corrective high shelf we added.
And sure enough, the same thing happens with Pro-Q3 in zero latency mode:
10k is no longer at zero phase, and this is what gets corrected in Natural Phase mode.
And in fact thats the only practical difference in Natural Phase mode. I see a lot of confusion
about this online: no it isn’t a halfway house between zero latency and linear phase.
At least, not in practical sense we need to consider as mix engineers. Natural Phase mode
is minimum phase, analogue style EQ, just like Zero Latency mode, and will behave the same way
as Zero Latency mode in every way except that phase response in the high frequencies.
Ok, thats enough for today. Thanks for watching.