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IR Length

Rex

Legend!
I guess my point is exactly what Rex said, that "there is no single inherent eq curve for a speaker" and when you listen to an actual speaker, you never here a single freq curve (except perhaps in the studio, where addition eq'ing is typical). However, present day irs do exactly that, they pick a single point. This makes me wonder if all the detail that an ir provides around a single eq axis is really necessary to represent the essential sound of a particular speaker. Maybe it does. But, to me, something seems limited by the way we are doing it.
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.


I'm just thinking... and I have already been warned about that, ...many times.
Never stop thinking. :)
 

RDH

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.



Never stop thinking. :)
Exactly! This is what I was getting at about different length frequency waves. You explained it much better. This has much more effect on what we hear in a room.
 

ChainOfThought

Experienced
So is there a difference in capturing room reflections on an ir VS traditionally recording a cab where reflections are happening in real time? Is there an audible benefit (subjectively) to recording a real cab and having those reflections on the recording? Does it basically just amount to a little bit of room reverb?

is the whole point here to remove any reflections from an ir so that we can go from there with a ‘dry’ signal and add back what we want? And basically some of the above is true, then the only way to model that would be absurdly long ir files which would introduce a slew of other issues, right?

i think I’m understanding it all but now I’m trying to take all this theoretical discussion and bring it back to practical application of what we have available now.
 

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?
 

AZG

Inspired
Lots of interesting discussion in this thread that has a lot of overlap with the thread over at TGP. Discussing it is fun, but nothing shows the value of far field reflection free IR like actually trying them for yourself. IMO letting the room you are actually playing in add the reflections or a reverb usually sounds better. TGP member gigsup has been kind enough to post some great far field IR to test for free. I recommend testing them with the 20ms/1024/normal setting.
 
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Admin M@

Administrator
Fractal Audio Systems
Moderator
So is there a difference in capturing room reflections on an ir VS traditionally recording a cab where reflections are happening in real time?
I don't think so, aside from the effect of the IR being a window. You will hear reflections in any "normal" recording. The point of this discussion though, I think, is that you might not necessarily want an IR to sound like a recording. Rather, you might want it to sound like the speaker itself, and free from reflections.
 

creativespiral

Inspired
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....
Radio controlled blimp with a downward facing microphone attached and small recorder? Point the cab directly up?
 

creativespiral

Inspired
then the blimp be be causing reflections :tearsofjoy:
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?
 

jon

Fractal Fanatic
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?
Well we can do like it has always been done since the first recording-point a mic and record/record that IR!

All we should do is like what Cliff was telling us this whole time - truncate the IR where the reflections start to occur :)

At the same time, he is working on something he had an 'eCliffany' about and lesson learned by all is that IRs should be shot in as LARGE a space as possible.

That's pretty much this thread in a nutshell :tearsofjoy:
 

creativespiral

Inspired
Well we can do like it has always been done since the first recording-point a mic and record/record that IR!

All we should do is like what Cliff was telling us this whole time - truncate the IR where the reflections start to occur :)

At the same time, he is working on something he had an 'eCliffany' about and lesson learned by all is that IRs should be shot in as LARGE a space as possible.

That's pretty much this thread in a nutshell :tearsofjoy:
Yeah, I get the truncating solution as an immediate improvement. That's a great insight.... and it sounds like we may see some ways to streamline or automate that truncation point soon.

But it seems current IR recordings must all be getting significant floor reflections... as Cliff mentioned, the idea of angling the cab slightly upward might improve IRs. I was just brainstorming on that and thinking, what about pointing cabinet directly upward 90 degrees and somehow getting mic up in the air above. That would remove floor reflections that may cause some additive or subtraction interference, and other early reflections, given the right space.
 

Rex

Legend!
is the whole point here to remove any reflections from an ir so that we can go from there with a ‘dry’ signal and add back what we want? And basically some of the above is true, then the only way to model that would be absurdly long ir files which would introduce a slew of other issues, right?
The point is to remove reflections from the IR. Because when you play through the IR, the room you’re in has reflections of its own.

But remember that you usually don’t hear these reflections as echoes. They come too fast for that. Instead, they sound like EQ added to your signal.
 

Rex

Legend!
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.
 

FractalAudio

Administrator
Fractal Audio Systems
Moderator
Yeah, I get the truncating solution as an immediate improvement. That's a great insight.... and it sounds like we may see some ways to streamline or automate that truncation point soon.

But it seems current IR recordings must all be getting significant floor reflections... as Cliff mentioned, the idea of angling the cab slightly upward might improve IRs. I was just brainstorming on that and thinking, what about pointing cabinet directly upward 90 degrees and somehow getting mic up in the air above. That would remove floor reflections that may cause some additive or subtraction interference, and other early reflections, given the right space.
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.
 

FractalAudio

Administrator
Fractal Audio Systems
Moderator
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.
 
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yeky83

Power User
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.
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?
 

ChainOfThought

Experienced
The point is to remove reflections from the IR. Because when you play through the IR, the room you’re in has reflections of its own.

But remember that you usually don’t hear these reflections as echoes. They come too fast for that. Instead, they sound like EQ added to your signal.
Gotcha, I only think of IR’s in terms of recording so I don’t really consider or care about what an ir sounds like in a room. I also fully realize I’m probably in a minority there, I play through an amp & cab for rehearsal and I don’t play live at all.

eta: and I definitely do get that you don’t hear them as echoes unless maybe you’re recording in a cave or a canyon. I’m kind of just trying to figure out how an ir that has one reflection captured works when compared to a real-time recording that’s catching all the reflections as you go. It’s basically a curiosity though, it’s not like I think the current recordings I’m getting from the axe2 sound or feel deficient to me in any way.

I think there’s something about ‘how’ ir’s work that I’m missing and creating a disconnect on the why for a lot of this stuff. On the plus side, it’s irrelevant because I’m not making or selling these things and cliff’s tips are easy to apply without digging this deep. It’s been a fun discussion though,even with the misinformation.
 
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jon

Fractal Fanatic
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 would say yes. Traditionally, recordings were typically done in large studios and recording spaces, and there's lots of reasons for that. The sound engineers back then had the right idea. Nowadays we are recording in bedrooms and offices and garages - all of which are great, as it affords the small man like you and I a chance to not have to sell our souls for enough to record an album, but it also is terrible for a lot of things - recording cymbals, vocals, choirs, you name it.

I can't remember a successful album recorded in a closet, the concept is the same here. Look at Van Halen in studio - not exactly a small space! (Or a clean space either, but that's another topic :tearsofjoy: )
 
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