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IR Length

joegold

Fractal Fanatic
I'd like to try messing around with this idea, but I'm using a II, not a III.
I have CabLab 3.4.2 also and tons of 3rd party IRs.

Can I use these tools somehow to experiment with shortening IRs (doesn't look like it) or do I need to use an audio app, like Audacity or Logic, to view and then shorten the IRs?
 

NeoSound

Fractal Fanatic
Air is not a dispersive medium at audio frequencies. The velocity is not a function of frequency.
I just learned that different sound frequencies travel at similar velocities through air so that guess was wrong. Still, I believe something that forms the low end of an amp is building before it affects the high end and we are capturing too much of that process with an ir.
 

hussamd

Power User
It would be nice to have a option in the editor to find this sweet spot or have it automatically figured out. I know you can do it :)
 

DLC86

Fractal Fanatic
I just learned that different sound frequencies travel at similar velocities through air so that guess was wrong. Still, I believe something that forms the low end of an amp is building before it affects the high end and we are capturing too much of that process with an ir.
Have you tried non-MPT IRs? Despite the fact that they sound identical to their min-phase version (in most cases) when listening to a recorded track, I find that changes the feel on low notes and the way the guitar interacts with the feedback from the speakers.

Maybe that's what you're hearing and it's actually the only way some frequencies could be heard as slightly delayed (eq and phase alterations happen due to "group delay" after all)
 

shatteredsquare

Fractal Fanatic
The reflections are slightly delayed in the real world but an ir captures that info the same point in time
you're tapping on the core of the idea but it's not frequency delay, it's comb filtering interaction that's constantly swirling, getting summed at the mic capsule, reflections in the real world are being slightly comb filtered constantly in varying amounts....where an IR is a static filter, snapshot. Time image, doesn't move.
 

FractalAudio

Administrator
Fractal Audio Systems
Moderator
you're tapping on the core of the idea but it's not frequency delay, it's comb filtering interaction that's constantly swirling, getting summed at the mic capsule, reflections in the real world are being slightly comb filtered constantly in varying amounts....where an IR is a static filter, snapshot. Time image, doesn't move.
No. The comb filtering doesn't vary. It only varies if the the source and/or receiver move.
 

shatteredsquare

Fractal Fanatic
It only varies if the the source and/or receiver move.
I know beyond the shadow of a doubt you are familiar with sympathetic resonance. At what dB does spl start physically moving stuff in measurable amounts? If a kick drum can rattle a snare, or a garbage truck can vibrate the ground, how much does it take to move a mic on a stand? Before it starts moving stuff around, how much SPL does it take to move a mic capsule? That mic capsule is moving constantly back and forth as it's sending signal, that's a source of modulation/distortion. With an IR, in the span of that ~1000ms window, the movement of that capsule as it got recorded for the IR is on a loop, it's static, and it sounds static, until you add a tiny bit of movement to it and it comes to life.
 

FractalAudio

Administrator
Fractal Audio Systems
Moderator
I know beyond the shadow of a doubt you are familiar with sympathetic resonance. At what dB does spl start physically moving stuff in measurable amounts? If a kick drum can rattle a snare, or a garbage truck can vibrate the ground, how much does it take to move a mic on a stand? Before it starts moving stuff around, how much SPL does it take to move a mic capsule? That mic capsule is moving constantly back and forth as it's sending signal, that's a source of modulation/distortion. With an IR, in the span of that ~1000ms window, the movement of that capsule as it got recorded for the IR is on a loop, it's static, and it sounds static, until you add a tiny bit of movement to it and it comes to life.
The mic doesn't send a signal. It's a receiver. Since the goal is to capture the response of the speaker as accurately as possible you want the mic to be as stationary as possible. If it moves it will distort the measurement. If the mic diaphragm doesn't move then it won't capture anything. That's the whole point. It's a transducer. It converts mechanical movement to electrical energy.
 

200man

Experienced
Yes, if it's quiet.

You could do far-field captures in there and reflection free near-field captures. Do a ground plane measurement for the far-field and raise the speaker well off the ground to do near-field.
hmmmm...way back when...Altec raised their boxes up in the air to measure their response....I looked for a picture, haven’t found it yet.
 

jon

Fractal Fanatic
If it's one thing this thread has taught me, is that everyone has an opinion even if they have no idea, how it works, or even if they hear a difference or not.

Also that some of us definitely were sleeping in physics class.

On a serious note though, if you don't understand what an IR is or what it does or how it works or even physics in general, please do some reading and understanding on the topic, Cliff is giving us great info and insight here and I honestly think the thread is getting cluttered with misconceptions and erroneous statements. Please do some research first and let's have a more informed discussion please guys.

Also, turn a knob and see if it makes a difference to YOU....most people claim to not hear the difference between firmwares but are experts on a couple milliseconds of a reflection? Come on guys.....
 

NeoSound

Fractal Fanatic
If it's one thing this thread has taught me, is that everyone has an opinion even if they have no idea, how it works, or even if they hear a difference or not.

Also that some of us definitely were sleeping in physics class.

On a serious note though, if you don't understand what an IR is or what it does or how it works or even physics in general, please do some reading and understanding on the topic, Cliff is giving us great info and insight here and I honestly think the thread is getting cluttered with misconceptions and erroneous statements. Please do some research first and let's have a more informed discussion please guys.

Also, turn a knob and see if it makes a difference to YOU....most people claim to not hear the difference between firmwares but are experts on a couple milliseconds of a reflection? Come on guys.....
even though there is science for most of this discussion, there is not for part of it. it's good to hear different opinions, even if not text book ones (imo :)) because if it was figured out and perfect already this thread and many others wouldn't exist. the technical background and terminology are nice to have so we don't go over things that have already been covered/discovered but that still doesn't make an opinion less valid until all is perfect (which may never happen?)
 

jon

Fractal Fanatic
Ideas, questions, insight and stuff like that are great tools that the non-technical can bring to the table....some great ideas are born that way!

However, arguing moot points and making uninformed statements that could be avoided with a little reading really is cluttering up a useful thread with nothing that adds value. Pretty sure if a little reading and understanding was done this thread would be half the length.....
 

Smilzo

Power User
The mic doesn't send a signal. It's a receiver. Since the goal is to capture the response of the speaker as accurately as possible you want the mic to be as stationary as possible. If it moves it will distort the measurement. If the mic diaphragm doesn't move then it won't capture anything. That's the whole point. It's a transducer. It converts mechanical movement to electrical energy.
Perhaps the OP was trying to suggest some kind of imperfection in the transducer that affect the capture of the IR with such level of details.
 

zenaxe

Fractal Fanatic
Thanks for clarifying, Cliff! Just wanted to make sure I was following along... It is definitely cool to hear your thinking and observations as you continue to explore (and push ;) ) the boundaries of modeling technology.

The cool thing about science and an open mind is you can change your point of view.

Edit: also, much of this is about personal taste. Which, of course, changes over time.
As noted, I was trying to clarify my understanding of Cliff's current thinking relative to prior developments or discussions. I am in science/technology myself (but not in audio, per se, hence wanting make sure I was following) and agree that it is completely counter-productive and anti-thetical to science to expect ideas to never change or never challenge them; in fact that would stop progress cold and is completely opposed to what the Fractal philosophy is and has what has made this place so great.
 
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jon

Fractal Fanatic
I know beyond the shadow of a doubt you are familiar with sympathetic resonance. At what dB does spl start physically moving stuff in measurable amounts? If a kick drum can rattle a snare, or a garbage truck can vibrate the ground, how much does it take to move a mic on a stand? Before it starts moving stuff around, how much SPL does it take to move a mic capsule? That mic capsule is moving constantly back and forth as it's sending signal, that's a source of modulation/distortion. With an IR, in the span of that ~1000ms window, the movement of that capsule as it got recorded for the IR is on a loop, it's static, and it sounds static, until you add a tiny bit of movement to it and it comes to life.
Perhaps the OP was trying to suggest some kind of imperfection in the transducer that affect the capture of the IR with such level of details.
In my understanding I think that he was implying that a loud noise would 'move' or shift the mic, resulting in an imperfect IR?
 

peteri

Experienced
This is a really interesting thread even if lots is over my head.

One question and sorry for dumbing it down. I’ve been using RAW format IRs when available over MPT. Now thinking this wasn’t the right idea?

Sorry to high jack the thread
 

fractalz

Experienced
I've been experimenting with IR length lately and keep finding that I like a shorter length. So I gave some thought to it and I think the reason is that a shorter IR trims off the early reflections.

As I stated over at The Argument Gear Page:
Aren't these artifacts mirroring what typically happens in a studio environment? Maybe the "free space" ones would sound "better". I'm just pointing out that it would no longer be the sound of a mic'd cab as we know it.

looking forward to the results of this thread. Maybe we'll get reflection-free IRs and wall/ceiling/floor distance parameters :)
 

FractalAudio

Administrator
Fractal Audio Systems
Moderator
This is a really interesting thread even if lots is over my head.

One question and sorry for dumbing it down. I’ve been using RAW format IRs when available over MPT. Now thinking this wasn’t the right idea?

Sorry to high jack the thread
Raw is technically "better" but the difference between raw and MPT is minimal. The disadvantage of raw is that you have to manually align them if you are mixing IRs.
 

peteri

Experienced
Raw is technically "better" but the difference between raw and MPT is minimal. The disadvantage of raw is that you have to manually align them if you are mixing IRs.
Thank you. Not only for the quick reply but also because I don’t need to reload them all!

After 10. I’m usually only using 1 IR so no harm done!
 
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