IRs made with tube amps (ML Sound Lab claims)

[HotRats]

Now who’s being pedantic?

I am, no doubts.

 

[Chocol8]

Unless two engineers make IR's of the same cab, using the same gear, then you quite literally have no ability to ascribe tonal differences to the engineer.

I get your point but on the other hand, we have had a ton of people capture thousands (10’s of thousands?) of IR’s of the same handful of 4x12’s with V30’s.

 

[FractalAudio]

Wait, what were we talking about?

Anyways... the reason that I, personally, use the "Mic + DI" method is that it doesn't matter how great your power amp is, there's a cable on its output (and connectors) and that cable has finite resistance.

For example, these vaunted old Crown power amps have advertised damping factors of over 1000. That implies an output impedance of less than 8 mohms. However, a typical speaker cable can have several tenths of an ohm of resistance. Let's assume 0.1 ohm on each conductor. That's 0.2 ohms total. This reduces your damping factor to 40. That's more than an order of magnitude worse.

It may not seem like much but those couple of a tenths of an ohm show up in the measurements. It's not huge, a few tenths of a dB, but it's not negligible either. I did some measurements at one point and the DI signal was definitely not flat. I seem to recall up to 1/2 dB with some speakers (4 ohms), maybe more.

Can you hear it? Dunno, but better to err on the side of accuracy.

 

[Chocol8]

Wait, what were we talking about?

A guy with Freddy Kruger syndrome, selling homeopathic remedies for the side effects of his homeopathic remedies, which then causes pedantic trolling over the inherent artistry involved in pointing an SM57 at a V30.

Come on, keep up!

 

[FractalAudio]

I forgot to add that the Mic + DI method compensates for ALL frequency response distortion, including the signal generator itself, between the signal generator and the amp and inside the amp.

 

[Chocol8]

I forgot to add that the Mic + DI method compensates for ALL frequency response distortion, including the signal generator itself, between the signal generator and the amp and inside the amp.

Now if we could only eliminate the mic and mic pre coloration as well.

 

[Boudoir Guitar]

Demonstrate to me how you know whether that (for example) 3kHz boost in your favourite IR came from a choice the engineer made, or whether it was a by-product of the speaker/cab/ir physical properties.

Exactly?

 

[FractalAudio]

Now if we could only eliminate the mic and mic pre coloration as well.

It's actually quite surprising how different pres can sound. Our Neve sounds considerably different than our API. All our Dyna-Cabs use the API now. The Neve sounds a little dull and bloated in comparison.

 

[Orvillain]

I get your point but on the other hand, we have had a ton of people capture thousands (10’s of thousands?) of IR’s of the same handful of 4x12’s with V30’s.

They all sound different.

 

[Chocol8]

They all sound different.

I haven't tried them all, but I agree many sound "different" and some are pretty "special". The real takeaway is different monkeys with the same gear get different results.

 

[Boudoir Guitar]

TGF approved IR marketing: “try mine. They sound a little different. I don’t purport to know why exactly.”

 

[MirrorProfiles]

What about moveable mic IR loaders? Are any of them actually handling interpolation properly?

Most cab engines normalise their IR’s individually, and then blend several together for each theoretical position. Interpolation works well accuracy wise, but the % of blend between them gets totally skewed by normalising level. That means when you’re blending multiple together, the balance between each goes off quite significantly and when you move to positions in between they’re not really accurate to actual positions. 50% between one and the other isn’t 50% anymore when they’re normalised by different amounts. I’ve heard of some 3D axis type cab engines blending up to 8 IR’s and they definitely normalise theirs. My guess in this is quite common as so many of them feel weird to me to drag a mic around as the frequencies don’t change in level in a proportional way any more.

There’s also the MPT thing which affects things like condenser mics (pressure based) vs dynamic mics (velocity based) which should be 90° out of phase with each other (at comparable positions).

 

[Orvillain]

TGF approved IR marketing: “try mine. They sound a little different. I don’t purport to know why exactly.”

I know exactly why.

 

[Orvillain]

I haven't tried them all, but I agree many sound "different" and some are pretty "special". The real takeaway is different monkeys with the same gear get different results.

It is literally different gear. My handmade neve clone sounds different to a Neve. And an other never.

 

[jay mitchell]

Anyways... the reason that I, personally, use the "Mic + DI" method is that it doesn't matter how great your power amp is, there's a cable on its output (and connectors) and that cable has finite resistance.

Let's investigate this, as we engineering-geek types are wont to do. (Beware: numbers and arithmetic lie ahead.)

14 gauge copper wire has resistance of 2.63 ohms/1000 ft. A 20-ft. cable from amp to speaker (40 feet of wire) of 14 ga. wire will have a resistance of .1 ohms. Using your Crown figure of 8mohm output resistance, that total resistance driving a speaker with a minimum impedance of four ohms will cause .23dB signal loss at the frequency of minimum impedance and about .017 dB at the frequency of resonance, assuming a peak impedance value of ~55 ohms. IOW, the voltage applied to the speaker will be about .21dB greater at resonance than at minimum impedance. If these worst-case numbers concern you, you have the options of increasing the gauge of your speaker cable and/or reducing its length. FYI, if you're testing a guitar cab with a 1/4" jack, odds are that the plug-jack contacts have more than .1 ohm resistance. That's still gonna be there even if you take a DI signal from the cab.

If you like to pretend that damping factor has real meaning, the above scenario reduces DF - which is frequency dependent, a fact that is widely ignored - from 500 to 35.5 at the frequency of minimum impedance and from 6875 at resonance (by far the most important region for DF) to 485. Neither reduction is consequential.

For example, these vaunted old Crown power amps have advertised damping factors of over 1000. That implies an output impedance of less than 8 mohms. However, a typical speaker cable can have several tenths of an ohm of resistance. Let's assume 0.1 ohm on each conductor. That's 0.2 ohms total. This reduces your damping factor to 40. That's more than an order of magnitude worse.

First, your cable resistance numbers are off. Not "several tenths," one tenth. There's a meaningful difference. And that's if you use a wimpy 14-ga. lamp cord that's 20 ft. long to drive a four-ohm speaker. Second, if the DF due to the amp is several orders of magnitude greater than it needs to be in order not to affect the speaker's response - it is in the case of the Crown - then reducing it an order of magnitude is inconsequential. If you use a shorter length of 12 ga. cable, the reduction in DF is even less.

It may not seem like much but those couple of a tenths of an ohm show up in the measurements. It's not huge, a few tenths of a dB, but it's not negligible either.

Given that test-to-test repeatibility of loudspeaker measurements - including any form of IR acquisition - is at least 1dB, and that 1-dB narrowband response deviations are inaudible, the difference you allege is negligible.

Pro tip: if you're truly concerned with acquiring the most accurate IRs possible, response changes due to speaker cabling are among the least of your worries. There are far bigger fish to fry before you obsess over minutia like this.

I did some measurements at one point and the DI signal was definitely not flat. I seem to recall up to 1/2 dB with some speakers (4 ohms), maybe more.

Can you hear it? Dunno, but better to err on the side of accuracy.

See above. The greatest possible response deviation - with 14 ga. lamp cord driving a four-ohm speaker - would be .21dB. There are quite a few areas in which accuracy could be improved with audible benefit. Speaker cable impedance is not one of them.

Another pro tip: a major challenge in engineering to identify the parameters that matter and those that don't and devote your resources to addressing the former.

 

[jay mitchell]

TGF approved IR marketing: “try mine. They sound a little different. I don’t purport to know why exactly.”

Silly as it sounds, that would amount to an unprecedented level of honesty.

 

[ian_dissonance]

(Thank you for your service.)

 

[jay mitchell]

What about moveable mic IR loaders? Are any of them actually handling interpolation properly?

Given that that is a physical impossibilty, no.

Interpolation works well accuracy wise,

Actually, it doesn't, and it can't.

There’s also the MPT thing which affects things like condenser mics (pressure based) vs dynamic mics (velocity based)

You got that wrong. The different mic types are directional (e.g., cardioid, hypercardioid, figure-of-eight) vs. pressure sensing (omni). Directional mics respond to acoustic [article velocity, whereas omni mics respond to acoustic pressure. Dynamic and condenser mics can be either cardioid or pressure sensing. A figure-of-eight mic is a ribbon type and must be dynamic.

 

[Sascha Franck]

Using a special "colorful" mic pre typically used for recording a guitar cabinet does not translate to IR capture.

It does, as long as it's a non-dynamic process happening.

Using a magic room known for great guitar cabinet recordings does not translate to IR capture.

And even that would do in case the maximum IR length would be sufficient.

Use of a "colorful" amp to record a guitar cabinet does not translate to IR capture.

Basically that's true as pretty much any amp has it's special dynamics, obviously that's especially true for tube amps.

However, I actually found myself ending up with some power amp coloration mixed into some self-shot IRs and liking it. So why not?

ain't nobody got time to try out every IR captured in a new and slightly funky way just to see what happens.

That's actually not true for me, the only difference being that I did the funky things on my own (but I also tried some other stuff, such as "no character" IRs and what not - and also liked some). The IRs I've used the most by an extremely wide margin over quite some years by now are 2-3 that are in no way what you'd usually get in any "typical" IR pack.

but what I'm definitely NOT missing out on is an IR that can give me something that sounds and feels more like playing through a tube amp because he used a tube amp to capture the IR.

That however is absolutely true.

 

[MirrorProfiles]

Given that that is a physical impossibilty, no.

Actually, it doesn't, and it can't.

You got that wrong. The different mic types are directional (e.g., cardioid, hypercardioid, figure-of-eight) vs. pressure sensing (omni). Directional mic respond to acoustic [article velocity, whereas omni mics respond to acoustic pressure. Dynamic and condenser mics can be either cardioid or pressure sensing. A figure-of-eight mic is a ribbon type and must be dynamic.

Cool. Well my questions still stand. And it’s all the more reason for mics to retain their original phase response.

Without going off on a tangent, what about condenser mics that have a figure of 8 pattern?