Why do some IR's and DynaCab's seem to compress more than others?

[boyce89976]

Did a search and couldn't find anything.

Over the past few weeks I've been trying to convert my main presets to DynaCabs, while trying some different IR's for a makeshift Matchless ESD cab. I used my latest DynaCab preset live a couple weeks ago. Sounded great at home, felt great... noted I had to increase amp level about 2dB to match my other presets.

Get to the gig, and between sets our FOH guy came up to ask if I was running more compression than usual (he makes his living as a recording engineer... great ear/knows his stuff). I said, no, why? He said, "I'm having trouble controlling your dynamics out front. Usually, I can set your fader and hardly have to touch it, but today I'm having to push you more than usual and pull you back more... I'm riding your fader way more than usual. Normally, you control your dynamics and I don't really have to think about it".

The only change I'd made to that preset was going to DynaCabs. Since then I've noticed some perceived compression differences between stock IR's as I try to construct a Matchless ESD cab. For example, the 4x12 Beatle A51 IR's seem significantly less compressed than the 4x12 Beatle 414 IR's.

I figure it's the IR's impedance interaction with the amp, and the way the amp's speaker compression/speaker drive settings are interacting (none of which was changed when changing from IR's to DynaCabs). Would love to hear some thoughts on this, as I've always thought IR's themselves are immune to compression.

 

[laxu]

Try turning off the "link speaker impedance curve" option and set the amp to something. Then try swapping Dyna-Cabs and see if the problem persists. If it doesn't, then it's basically different speaker impedance curves reacting with the amp.

 

[Smittefar]

Also, check if you have the preamp saturation activated in the cab block.

It could also just be that the new cab had frequencies that poke through the mix more

 

[Chromatizm]

This topic is very interesting to me. I'm looking for ways to get as much "natural" compression, without CMP blocks, as possible from amp and cab, to make legato playing easier and more consistent.
I know a few tricks for the amp block, but would like to understand if some cabs actually add more compression to help with this while not complete smashing the attack. I use preamp section of Cab block, but never thought about differences speakers may introduce to support this.
Would really like to learn if there are some IRs which are better for this.

 

[Dave Merrill]

This topic is very interesting to me. I'm looking for ways to get as much "natural" compression, without CMP blocks, as possible from amp and cab, to make legato playing easier and more consistent.
I know a few tricks for the amp block, but would like to understand if some cabs actually add more compression to help with this while not complete smashing the attack. I use preamp section of Cab block, but never thought about differences speakers may introduce to support this.
Would really like to learn if there are some IRs which are better for this.

Impulse responses do not actually compress, any of them, at all. They operate in the frequency domain only, like a multi-point eq. That's more or less a fact.

Any apparent compression is really just that.

 

[Chromatizm]

Impulse responses do not actually compress, any of them, at all.

Right, this part I understand.
But the speakers which were used to make an IR - they DO compress, don't they? Which naturally converts into IR "compression".
Or not?

 

[scarbodave]

Right, this part I understand.
But the speakers which were used to make an IR - they DO compress, don't they? Which naturally converts into IR "compression".
Or not?

I believe speaker compression is modeled as part of the amp block. The IRs are linear and do not replicate speaker compression.

 

[Chromatizm]

I believe speaker compression is modeled as part of the amp block. The IRs are linear and do not replicate speaker compression.

So to check if I get this correctly: even if the speaker is a low-wattage one which starts to compress/distort quickly, the method of creating/capturing IRs excludes this effect from the end result (IR)?

 

[scarbodave]

So to check if I get this correctly: even if the speaker is a low-wattage one which starts to compress/distort quickly, the method of creating/capturing IRs excludes this effect from the end result (IR)?

I am not certain, but this is my understanding....hopefully someone can correct me if need be.

I believe the IR will capture whatever distortions/compression the speaker is exhibiting at the time of the capture. However, when using the IR in a modeler these distortions are not sensitive to the input signal to the cab block, they are constant. Therefore, you will not experience the speaker compression/distortion in the same way as playing through the original speaker which is sensitive to the level fed to the speaker.

 

[Reet]

I'm also trying to convert my sounds to dyna cabs. What scarbodave said makes alot of sense to me also.

 

[steadystate]

Right, this part I understand.
But the speakers which were used to make an IR - they DO compress, don't they? Which naturally converts into IR "compression".
Or not?

Not.

 

[Dave Merrill]

Not.

^^^ This.

 

[Greg Ferguson]

I am not certain, but this is my understanding....hopefully someone can correct me if need be.

I believe the IR will capture whatever distortions/compression the speaker is exhibiting at the time of the capture. However, when using the IR in a modeler these distortions are not sensitive to the input signal to the cab block, they are constant. Therefore, you will not experience the speaker compression/distortion in the same way as playing through the original speaker which is sensitive to the level fed to the speaker.

As I understand it…

The IR is basically an EQ curve and is linear. It doesn’t affect compression or distortion or feel.

The speaker impedance curve is applied inside the amp block and affects the power-amp, which is where the compression and clipping occur and those affect the feel.

Both are important, but in different ways, and both together affect the authenticity of the sound and feel of the Amp+Cab block. Matching the SIC and the IR is usually desirable so the firmware now tries to make that easier for us, but we might not always want that because we might want to emulate the sound of a stock cabinet that has different speakers in it, so we can pick the IR for the cabinet and the SIC for the speakers and land somewhere in-between.

There’s a lot of information about this in the Amp and Cab block pages in the Wiki.

 

[boyce89976]

Impulse responses do not actually compress, any of them, at all. They operate in the frequency domain only, like a multi-point eq. That's more or less a fact.

Any apparent compression is really just that.

This is my understanding, but in practice there are definitely some differences in the way the IR reacts and feels under the fingers. If I have some time I'll post a couple presets with the two cabs I've found with the biggest differences in feel.

 

[randocaster]

I remember Jay Mitchell saying that loudspeakers are very linear up to the point of basically blowing up. And a properly functioning speaker does not compress.

 

[NotGlenn]

I remember Jay Mitchell saying that loudspeakers are very linear up to the point of basically blowing up. And a properly functioning speaker does not compress.

He may have been talking about PA speakers, because guitar speakers definitely do compress and distort to varying degrees depending on the type of speaker and level being fed into it.

 

[unix-guy]

He may have been talking about PA speakers, because guitar speakers definitely do compress and distort to varying degrees depending on the type of speaker and level being fed into it.

Which is why the Amp block has a setting for speaker compression

 

[randocaster]

He may have been talking about PA speakers, because guitar speakers definitely do compress and distort to varying degrees depending on the type of speaker and level being fed into it.

This is one of the posts I was thinking of:

"Speakers "compressing" is a myth. Compression is a change in gain in response to the envelope (which only can occur over several cycles) of a signal. Speaker nonlinearities are all responses to peaks that occur within a single cycle. Any such nonlinearities would therefore constitute clipping. In case anyone doesn't know this, I'll point out that clipping and compression sound very, very different."

And this:
"

Don't speakers compress mechanically?

No. They have a limited range of linear travel, but driving them beyond that range causes clipping, not compression. I refer you to the post of mine you quoted for the difference between the two.

They can mechanically clip when driven to extreme possible positions, but even within those extremes there are softer non-linearities.

Soft clipping is still clipping; it is quite different from compression.

Near the end of its travel in both directions, it faces more mechanical resistance than it does at the middle or resting position.

You're unintentionally misusing the phrase "mechanical resistance." Mechanical resistance is proportional to velocity of motion, not displacement from rest. In fact, velocity - and therefore the force due to mechanical resistance - reaches zero at maximum displacement. The phrase you need is spring constant. While it is true that the restorative force due to the spring constant of the suspension increases with displacement from rest, it is also true that this force is linear and therefore causes no nonlinear behavior, as long as the cone's displacement lies within its linear range. Displacement beyond the linear range in a guitar speaker only occurs at low frequencies and causes obvious and objectionable distortion. That sound is not part of any iconic guitar tone."

YMMV and all that.

 

[Stratoblaster]

This is my understanding, but in practice there are definitely some differences in the way the IR reacts and feels under the fingers. If I have some time I'll post a couple presets with the two cabs I've found with the biggest differences in feel.

This mirrors my experience with IR's; over the years I've chosen certain ones to work with based on the feel I got when using them, irrespective of amp tweaks, etc. Even though IR's are just high-res EQ's, in a sense, and linear, IME they can, and do, affect the feel.

 

[giantslayer]

IR’s are more than just an EQ curve. There is also a time component. Heck, IR’s can even be used to create reverb.