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IR Length

creativespiral

Inspired
The problem with pointing it straight up is that it limits the mics you can use. Ribbon mics don't work well when oriented horizontally. The ribbon is designed to be vertical. Also, pointing straight up exaggerates the ceiling reflection.
Yeah, I guess it wouldn't be optimal for ribbon mics, but for dynamic/condenser? Also, was thinking of an open roof type of stadium situation... or out in the desert on a calm and quiet night, where you have no ceiling? I dunno - have never done IR recording myself... just brainstorming possibilities to eliminate floor reflections, which I assume must cause some fairly substantial additive and subtractive interference in IR recordings.
 

CodePoet

Power User
Would it be correct to takeaway that this is a good practice not only in capturing IRs but also when mic'ing guitar amps in general for recording/playing?
I think it depends on what you're after and I don't think this changes general recording practices. Micing an amp has always given you some room flavor - that's part of the sound you get when doing it. Pulling the mic back to get more room is certainly a technique that's used.

I think the discussion here is if you're after the most unaffected/direct cab sound then work towards eliminating your early reflections. This allows you the cleanest signal to add in your own room sound if you wish. But it's all what you think works for you. Cliff was stating he was preferring the sound of some IRs when they were shorter and eliminating those early reflections may be the reason why.
 

VidarAus

Inspired
Cover the room in corrugated foam. It'll be dead. My bedroom is this way. Dead.
I imagine it would be dead for higher frequency ringing/flutter (like, dead from reflections when clapping hands). Is probably super uncomfortable to be in for long periods. But bass build up would be unaffected. I used to have a room like this and thought for a long time that it sounded good. It didn’t. Did some mic measurements which confirmed my eventual feeling on the matter. Got rid of the foam. Decided I had to do it properly or not at all - and properly would kill my wallet and my wife would kill me ;)

Not saying this is your room, as I have no idea how you have it treated. Just adding to the off topic idle musing in this thread.
 
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VidarAus

Inspired
The takeaways from this are simple:
1. Minimize reflections as much as possible when capturing IRs. Shoot them in the largest room you can find. Elevate the speaker off the floor or angle it back to minimize the floor reflection. Make sure there is ample distance behind an open-back cabinet.

2. For existing IRs that may have prominent room reflections try different IR lengths to trim out the reflections.
Great summary - thanks Cliff. And if you happen to add an algorithm to automatically trim for us (user selectable of course!), or provide graphing functionality in Axe Edit, we can confirm visually as well ;)
 

lauke-lux

Power User
My opinion is that you arrive at the limit of what can be measured or simulated. Ideally an enormous capture room would permit to capture ir's wo réflexions. But then there's cab reflexions, which explains why we better like some speaker in other cabs than other speakers (or some girls mothers better than other girls mothers). Hence I guess even the density or water weight (Not RH which is a bad inducator) of the air does impact listening expérience. Aren't we on the limit of what numeric calculations can achieve ?
 

Corinthian

Inspired
Hmm... yeah, I was thinking unidirectional mic, but even in that case, I guess you have sound reflections back from behind the mic (off of a theoretical RC blimp)?

Mic and small recorder suspended from a cable over/across a stadium?... Cab pointing upward to suspended mic.

Just brainstorming options to get rid of floor reflections (and other early reflections). Not saying they're cheap or easy options, but what would be the "ideal control setting" for IR recording?
Avoiding floor reflections (at least in the frequencies we're concerned with) is quite simple: https://www.prosoundtraining.com/2014/04/24/ground-plane-measurements/
 

Stratoblaster

Fractal Fanatic
And that brings me back to question about the possibility of a "Modeled IR" -- zero reflections.
I've been experimenting with generated/modeled IR's for a few weeks now and am starting to think this may be the way to go for many reasons. I've gotten some amazing results with them and am now preferring them over conventional/captured IR's somewhat. At my last gig I used a generated IR exclusively and am absolutely enthralled with generating them now.

I have to play around with them more but frankly, I've never heard my Fractal gear sound as good as it does now with the results of my latest iteration. I love being able to control, at a deep level, the entire process which negates reflections and the many artifacts (proximity, excessive comb-filtering, etc.) that affect mic captures. They have an overall clarity, richness, and detail that I've not generally found in conventional IR's and again, I can control/tweak at a 'root' level. I'm very excited about all of this...

Promising stuff for sure...I can see synthetic IR's gaining traction as things develop...
 

VidarAus

Inspired
I've been experimenting with generated/modeled IR's for a few weeks now and am starting to think this may be the way to go for many reasons. I've gotten some amazing results with them and am now preferring them over conventional/captured IR's somewhat. At my last gig I used a generated IR exclusively and am absolutely enthralled with generating them now.

I have to play around with them more but frankly, I've never heard my Fractal gear sound as good as it does now with the results of my latest iteration. I love being able to control, at a deep level, the entire process which negates reflections and the many artifacts (proximity, excessive comb-filtering, etc.) that affect mic captures. They have an overall clarity, richness, and detail that I've not generally found in conventional IR's and again, I can control/tweak at a 'root' level. I'm very excited about all of this...

Promising stuff for sure...I can see synthetic IR's gaining traction as things develop...
How do you generate a synthetic IR? What tools are you using?
 

Corinthian

Inspired
That doesn't work for near-field measurements and you need a really large space or you need to do it outdoors. We tried it in our warehouse and the results still had reflections.
Yes, not practical for near field.

What caused the reflections in your warehouse? Weren’t there some roof struts or something?
 

Stratoblaster

Fractal Fanatic
How do you generate a synthetic IR? What tools are you using?
I'm using this absolutely fantastic freeware (IR Workshop):

https://github.com/ValdemarOrn/IRWorkshop

The user guide:
https://github.com/ValdemarOrn/IRWorkshop/blob/master/Guide/Readme.md

It's complex and has a bit of a learning curve, but you can do a lot of deep tweaking with it. It's very option rich and I'm getting killer results from it. You can do so much with it to process/manipulate/generate IR's.

I export the IR as a .wav, load and convert it to .syx with CabLab. A bit of a process but I've got a fairly efficient workflow going with the various pieces.

One thing I'm finding is that I'm preferring the overall sound of a PEQ block before the AMP block to add girth/fatness around ~500Hz -> 600Hz vs baking that in post-AMP in the CAB block.

Again, I'm finding impressive results with it, and my time spent refining and playing with IR Workshop is paying off big time. I have astounding control over the generating process with the software, and I can't help but think generated IR's can be 'a thing' and maybe an evolution/addition to the all important IR component in cab modeling.
 
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Joe Bfstplk

Fractal Fanatic
You're right. An IR cannot fully capture the sound of a speaker cab in a room. But it's not that the detail in an IR is too much information. Rather, it's incomplete information. All those different EQ curves and levels — the sound coming straight down the bore of a speaker, the sound radiating at different angles, the sound coming off the back of the cab — form a complex soup of different sounds that radiate out, and bounce off the walls, floor and ceiling in different amounts and at different times and phases. The way those sounds mix is different at every point in the room, and it changes as you move around. An IR can't capture all of that. It is, as you say, a single capture of some of the many things that the cab does.
With that in mind, I would think a good close mic'ed IR or two ought to be best to bring the sound of the source into whatever room it is being played into, which would support the "cut it off before the first reflection" viewpoint.
 
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jon

Fractal Fanatic
Very valid point - recordings of amps and cabs in a studio would be FULL of all these reflections. Never stopped anyone from making recordings all these decades.

Ideally there would be no reflections in an IR but this would be quite challenging to practically achieve. Sound travels at about 343m/s, so even at 40ms, sound has already travelled roughly 14m! A typical 500ms IR would mean the sound has traveled over 170m! (1m = 3.2ft) An IR of 100ms means it would have travelled 34m.

So you see the challenge - having NO reflective surface would mean suspending a cab high up in an aircraft hanger or football field! Not really practical unless you happen to have a football field and a blimp at your disposal....

Also goes to show you - most of us never gave this a fleeting consideration before Cliff mentioned it. Now we're nit picking about something that has existed in recordings from the dawn of recording time, insisting that it's the cause of all our tonal woes. Irony no?
With that in mind, I would think a good close mic'ed IR or two ought to be best to bring the sound of the source into whatever room it is being played into, which would support the "cut it iff before the first reflection" viewpoint.
Being closer to the source makes no difference- as I was discussing in my earlier post - sound travels so fast that even for a 40 ms IR you need a room 50ft large! And the cab suspended or angled somehow so the sound reflection from the floor doesn't enter the picture....not really practical.....hell even when Cliff tried shooting it in the warehouse he was getting reflections...sound travels too fast, which is a point I think most of us are missing here....

The best solution so far is truncation of the IR like Cliff was saying or the synthetic IR seems to have some potential there as well...
 

Joe Bfstplk

Fractal Fanatic
There are situations, though, where you might actually want to keep those reflections. Like when you’re playing an outdoor gig, and there’s no room causing reflections in the first place.
Seems like a case for setting up a reverb block right after the cab with a knob on the performance tab, set up with just early reflections, so you have easy access to liven up a dead space or outdoor area.
 

AZG

Inspired
Being closer to the source makes no difference- as I was discussing in my earlier post - sound travels so fast that even for a 40 ms IR you need a room 50ft large! And the cab suspended or angled somehow so the sound reflection from the floor doesn't enter the picture....not really practical.....hell even when Cliff tried shooting it in the warehouse he was getting reflections...sound travels too fast, which is a point I think most of us are missing here....

The best solution so far is truncation of the IR like Cliff was saying or the synthetic IR seems to have some potential there as well...
My understand is that 20ms is enough to capture the cab. Almost everything after 20ms is room, and you need far more than 40ms or even 200ms to actually capture the room. Capture just the cab and let the room you are playing in add the room or use a reverb. Try out the free far field reflection free IR from my earlier post and see for yourself. https://forum.fractalaudio.com/threads/ir-length.155295/page-8#post-1849010
 

yeky83

Power User
Seems like a case for setting up a reverb block right after the cab with a knob on the performance tab, set up with just early reflections, so you have easy access to liven up a dead space or outdoor area.
For just the early reflection stuff, options are already available within the cab block itself! :)
 

Joe Bfstplk

Fractal Fanatic
For just the early reflection stuff, options are already available within the cab block itself! :)
True.

Question is, are those able to be put on the performance tab? I haven't tried, so I don't honestly know.

Other question, if you have two cabs, do you need two knobs?
 
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