Impulse Responses are Just EQ

[ian_dissonance]

What I was thinking is more that guitarists (and I'm speaking about myself here) should get more comfortable with EQ'ing their presets rather than just flipping through (and buying more) IR's. I'm guilty of that for sure. A couple weeks ago I spent 5 minutes with a graphic EQ using the old standard legacy 103 IR which sounded way too dull and mushy, and I had a fantastic tone I was really happy with.

Guitarists would do well to learn as much as they can about audio in general.

 

[Orvillain]

Dan Worrall laughs at your four winds!

 

[Chocol8]

humans are allowing themselves to become stupid.

There have always been a lot of stupid humans. The difference these days is there are no saber tooth tigers for them to pet so more of the stupid ones survive to adulthood and reproduce. They also now have the benefit of the Internet so they can share their stupidity without being filtered by content curators.

 

[CorrosiveMatter]

There have always been a lot of stupid humans. The difference these days is there are no saber tooth tigers for them to pet so more of the stupid ones survive to adulthood and reproduce. They also now have the benefit of the Internet so they can share their stupidity without being filtered by content curators.

We should have let them eat the tide pods....

 

[newholland]

There have always been a lot of stupid humans. The difference these days is there are no saber tooth tigers for them to pet so more of the stupid ones survive to adulthood and reproduce. They also now have the benefit of the Internet so they can share their stupidity without being filtered by content curators.

i was pretending to not be a curmudgeon, but yeah, i aint gonna disagree witcher.

 

[Frodebro]

While this is true from a UI perspective, it is not really true from a DSP perspective.

An EQ filter is an LTI system. Fully described by its transfer function. For minimum phase systems, shifts in the magnitude response also cause shifts in the phase response. The two are inseparably linked; this is known as the Hilbert transform relationship; which only holds for minimum-phase systems.

Whenever an EQ boosts or cuts frequencies, it is simultaneously introducing frequency dependent phase shifts.

So it is literally true that for minimum-phase EQ's (the most common) you simply could not EQ a signal without causing phase alterations.

All-pass filters are another case. They alter the phase response while leaving the magnitude completely flat. So phase manipulation can exist independently, but magnitude shaping without affecting phase is not possible in minimum-phase systems.

In EQ design, the only way to decouple magnitude and phase is with FIR based designs - ie; linear phase EQ's.

Finally, there is some truth to the idea that IR's are just EQ.

- LTI systems. Captures the impulse response of the cabinet+mic+room, etc.
- Convolution with that IR == multiplication of the input spectrum with the IR frequency response.
- In that sense, a cab IR is an arbitrary LTI filter. In practice it captures fine-grained magnitude and phase detail that far exceeds what your typical EQ section would offer. But the underlying DSP mechanisms are the same.

But let's be clear - an IR is not just a handful of EQ bands, as a typical user would understand it. IR's also capture time-domain behaviour. EQ's do not replicate that, at least on the user experience side. IR's are also not limited to minimum-phase filters.

So as ever, it is more complex than a clickbait Youtube thumbnail.

And with a single post our favorite cunt reveals that yes, he was a member of the chess club in school.

 

[AlbertA]

While this is true from a UI perspective, it is not really true from a DSP perspective.

Yes I was referring to purposefully controlling the phase by the user.

An EQ filter is an LTI system. Fully described by its transfer function. For minimum phase systems, shifts in the magnitude response also cause shifts in the phase response. The two are inseparably linked; this is known as the Hilbert transform relationship; which only holds for minimum-phase systems.

Whenever an EQ boosts or cuts frequencies, it is simultaneously introducing frequency dependent phase shifts.

Yep.

So it is literally true that for minimum-phase EQ's (the most common) you simply could not EQ a signal without causing phase alterations.

Correct.

But let's be clear - an IR is not just a handful of EQ bands, as a typical user would understand it. IR's also capture time-domain behaviour. EQ's do not replicate that, at least on the user experience side. IR's are also not limited to minimum-phase filters.

Yes exactly.

 

[Orvillain]

 

[Orvillain]

And with a single post our favorite cunt reveals that yes, he was a member of the chess club in school.

Nah, I'm shit at chess. Too much dimensionality.

 

[Mikael Dez]

Nah, I'm shit at chess. Too much dimensionality.

I beat my step dad in chess so bad he threw the board across the room after a couple hours he was an asshole but I admittedly had a shit eating grin the whole time

 

[Lele]

IR's also capture time-domain behaviour. EQ's do not replicate that, at least on the user experience side.

Okay, but how significant is this behavior when using a speaker/mic simulation with an impulse response that’s only about 20 ms long?

I’m in the camp that sees an IR as essentially a very detailed equalizer with countless tap points—something you generally can’t replicate with a standard EQ. But if you’re okay with some rounding and don’t demand a perfect recreation of a speaker/mic response, then an IR is just an EQ, at least when we’re talking about cab/mic simulation.

 

[Orvillain]

Okay, but how significant is this behavior when using a speaker/mic simulation with an impulse response that’s only about 20 ms long?

20ms may very well under-represent low frequency ringing or port resonances, which matters for bass cabs or open-backed cabs I'd wager.

It also wouldn't give you much room for late reflections, which the further away the mic is from the speaker, the more impact on the final tone it is going to have.

EQ itself won't replicate the group delay effects that affect transient feel. It'll work in a pinch - say the tonematch block on Axe3, or tonematching using Fabfilter's EQ plugin - but it won't be as accurate as a good quality IR.

I think Fractal with their UltraRes resolution - about 170ms iirc - probably captures as much as you'll ever need in most contexts. I don't see any need to go longer than that.

When I compare my own IR's running inside Cab Lab 4, versus running directly on my Suhr Reactive Load IR, I definitely hear a quality difference. The Suhr seems to crop them, and I lose some resolution.