IR Length

[RDH]

No, I'm just talking about the distance it takes for 100hz to travel one complete cycle. Now whether or not it effects the curve we capture from a cab closer than that distance, I have no idea.

Basically, IIRC the length of a sound wave gets shorter as the frequencies get higher. Close mixing won't be affected much because the waves reach the Mic relatively at the same time, as well as a distance at the same time, however the effect of the different wave lengths show their stuff when they start reflecting off surfaces ex: a 20hz wave will reflect once at a distance of 20 ft where a 20kz wave will reflect many times the effect is in the reflections.

 

[VidarAus]

Are people removing low cuts on heavy, chugger-chugger type presets and still getting good results? Or is this working better for other styles?

 

[bdrepko]

As I stated over at The Argument Gear Page:

Now that funny!

 

[guitarmike]

Basically, IIRC the length of a sound wave gets shorter as the frequencies get higher. Close mixing won't be affected much because the waves reach the Mic relatively at the same time, as well as a distance at the same time, however the effect of the different wave lengths show their stuff when they start reflecting off surfaces ex: a 20hz wave will reflect once at a distance of 20 ft where a 20kz wave will reflect many times the effect is in the reflections.

From Jay Mitchell:
"When you place a mic in the near field of a speaker, the response at low frequencies is its half space response (as if the speaker had been recessed into a wall). That adds 6dB to the low frequency level as compared to the free field response. Furthermore, when you close-mic an open back cab like this one, the cancellation of low frequencies that acoustic dipoles naturally produce is absent. There is also the proximity effect of the microphone, which exaggerates low frequencies when the mic is close to the source. That effect will always be present with a directional mic (not with an omni, though)."

Maybe this is why I find ir's bass heavy... Perhaps close micing and the distance it takes for a freq to complete a full cycle does matter. It is pretty well know that close miking is usual in recording studios, but they are also known for cutting lows. In the quest for the perfect representation of the cab eq curve, wouldn't this need to be addressed?

 

[Perdikament]

I've been playing with ir length and the cab block again. The air parameter set to about 60%, then setting the ir length to add desired bass content and cab flavor (longer is bassier) sounds the most natural and clear as far as tube amp sounds imo. My guess as to why it responds this way would be that high frequency content from a real amp hits our ears faster than the bass content and an ir is capturing all of this information at the same point in time which causes all kinds of phaseyness. We probably still get this phaseyness and bounced around lows with a real amp but slightly after getting the high frequency content?

Adding “Air” is just bypassing the cab block. That’s what the Air parameter does, it’s like taking a line straight off the head & directly into the board, no speakers.

 

[jon]

Maybe this is why I find ir's bass heavy... Perhaps close micing and the distance it takes for a freq to complete a full cycle does matter. It is pretty well know that close miking is usual in recording studios, but they are also known for cutting lows. In the quest for the perfect representation of the cab eq curve, wouldn't this need to be addressed?

In my experience I have found the opposite to be true - amp and cab tend to be more 'bass heavy' than the axe and IR....what are you running the axe through? The HS8's?

 

[antcarrier]

Maybe this is why I find ir's bass heavy... Perhaps close micing and the distance it takes for a freq to complete a full cycle does matter. It is pretty well know that close miking is usual in recording studios, but they are also known for cutting lows. In the quest for the perfect representation of the cab eq curve, wouldn't this need to be addressed?

The time-of-flight distance required for a a specific frequency to complete a cycle does not matter. Low frequencies can be captured accurately in an IR without extended distance. That is, they are accurate to where the mic is positioned relative to the cab. What determines the accuracy of low frequencies in an IR is the length of the IR. You may prefer the sound of a far field IR at 3 meters (some of my favourite IRs are at 3m distance), but it doesn't have anything to do with completed cycles of low frequencies in the time-of-flight.

 

[Perdikament]

yes, but it has a selectable frequency and it does add clarity.

I didn’t know if you knew that’s what it does, a lot of people don’t... that’s why when ya said 60% I was thinking that was pretty high as I know when I messed with it a few times I thought 15% was kind of getting to be too much. I forget exactly what freq I had it at, I think it was somewhere around 3-4K, but ultimately it’s just something I never use.

 

[antcarrier]

Here is an example of what room reflections do:

Here is a reflection free IR windowed to 37ms:


Here is the same IR windowed to 45ms. There are significant room reflections from 41ms.

 

[guitarmike]

In my experience I have found the opposite to be true - amp and cab tend to be more 'bass heavy' than the axe and IR....what are you running the axe through? The HS8's?

Yep...

 

[FractalAudio]

Here is an example of what room reflections do:

Here is a reflection free IR windowed to 37ms:
View attachment 59764

Here is the same IR windowed to 45ms. There are significant room reflections from 41ms.
View attachment 59765

That's the point of this thread. It's a shame it didn't stay on topic.

 

[guitarmike]

The time-of-flight distance required for a a specific frequency to complete a cycle does not matter. Low frequencies can be captured accurately in an IR without extended distance. That is, they are accurate to where the mic is positioned relative to the cab. What determines the accuracy of low frequencies in an IR is the length of the IR. You may prefer the sound of a far field IR at 3 meters (some of my favourite IRs are at 3m distance), but it doesn't have anything to do with completed cycles of low frequencies in the time-of-flight.

In what way have I misinterpreted what Mr Mitchell stated in his post that was referenced by DLC86?

 

[Johnny Rigs]

So, reading past the noise, my understanding is that the point of this thread is: your longer length IRs contain some amount of early reflections in them. If you want to cut their effect out, reduce the sample length of your IR.

This currently seems more feasible than reflection-free IRs, due to availability and selection.

 

[guitarmike]

That's the point of this thread. It's a shame it didn't stay on topic.

Those are significant room reflections? This amount of eq curve difference is audible?

 

[jon]

Here is an example of what room reflections do:

Here is a reflection free IR windowed to 37ms:
View attachment 59764

Here is the same IR windowed to 45ms. There are significant room reflections from 41ms.
View attachment 59765

Man, that red for me is REALLY hard for my old eyes to see, can you post it back up in white or something pretty please?

 

[antcarrier]

Those are significant room reflections? This amount of eq curve difference is audible?

Actually, because of the type of the window used, the room reflections at 41ms were attenuated to -43db.
Now in white - here is the same IR with a 45 ms rectangular window (not good practice). The room reflections now have a maximum amplitude of -32db.



For reference, 37 ms again, reflection free. For a fair comparison a rectangular window is also appleid.



Note that this is a far field IR. With near field IRs, room reflections will be of significantly less amplitude.

 

[jon]

Hey thanks @antcarrier! That white pen is WAAAAAY easier to see! Very obvious now, appreciate it!

 

[yyz67]

There is no single inherent EQ curve of a room, just as there is no single inherent EQ curve of a guitar cab.

Yes. Nor of a guitar. Nor for any extended source, i.e. real object or real room/space.

@guitarmike To experience this for yourself in a room, generate a sine wave at a fixed freq and play it through your sound system or rig (mono through one speaker is ideal but stereo can work). If you walk around your room you can hear peaks and notches. Bass buildup in corners can be particularly loud.

You can use a "room mode" calculator to help find frequencies that are resonant with your room like http://www.mcsquared.com/modecalc.htm. It won't be perfect but it can give a starting point for particularly resonant (and anti-resonant) freqs.

 

[guitarmike]

Yes. Nor of a guitar. Nor for any extended source, i.e. real object or real room/space.

@guitarmike To experience this for yourself in a room, generate a sine wave at a fixed freq and play it through your sound system or rig (mono through one speaker is ideal but stereo can work). If you walk around your room you can hear peaks and notches. Bass buildup in corners can be particularly loud.

You can use a "room mode" calculator to help find frequencies that are resonant with your room like http://www.mcsquared.com/modecalc.htm. It won't be perfect but it can give a starting point for particularly resonant (and anti-resonant) freqs.

Yes you are right! I have even measured it. It really is amazing how much the room affects the sound. I think I have actually tried the "mcsquared" modeling and a few others. It seems best to do actual measurements...methodically all over the room. Especially where I'm sittin'. I typically use the "room eq" software.
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. Of course there are work arounds and the Fractal provides all the tools needed to produce state of the art guitar sounds. I wish I was smart enough to figure it, but alas, I'm a dumb ass. Good thing smart people like Cliff are on the job. I really don't have to worry about it because the state of the art will continue to pour out from this company reguardless of my input. I'm just thinking... and I have already been warned about that, ...many times. Cliff, sorry to take this off track.

 

[jon]

Yes I think you're starting to get it a bit now

I think you may still be missing the point on what an IR is in the first place, but you're starting to see the light.

If you want to 'average out' the sound of the speaker like you want to do, why not try a mix of several IRs of the same speaker at different distances and angles? That's as 'average' as you can get with the existing technology and the laws of physics right now.

Lots of users have done this too - use a far field IR together with a close mic'd IR of the same speaker. You want an average, so take many IRs of the same speaker at different angles and distances and there you go.

Not quite what this thread is about, but we're all learning here! Try it and see if it works for you.

Edit: a tool like cab lab should give you the results you are looking for