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*FREE* Far-Field Session #2 Cab Pack for Axe-Fx Users

Lilarcor

Inspired
I'm wondering whats going on with the Recto cab IRs at 0° angle. Both A and B seem really thin, trebly and scratchy compared to those IRs shot at an angle. The other cabs don't show this behavior. Is it because this Recto cab is just a lot more directional than the other cabs?
 

Corinthian

Regular
Hey Leon, Can you do a Vdo about this topic.? That will really help some of us understand what's it all about?
Here's a simple, if a little long-winded, explanation:

The premise is that close micing a cab is problematic (from a technical standpoint at least... you might like the sound and it's what engineers have been using for years) for a few reasons:
  • Speaker cabinets produce sound from more than just the speaker and when you listen to a real cab in a room you're hearing the sound coming from the cab as a whole, not just the speaker. Close micing picks up very little of the sound from elsewhere because the mic is close to the speaker.
  • If the cabinet has multiple speakers the mic only picks up sound from one.
  • Many mics exhibit proximity effects increasing the bass response when they are close to the sound source.
  • The sound from the speaker bounces off the floor causing peaks and nuls in the waveform because of phasing (meaning that some frequencies are pronounced and others too quiet in an unnatural way.
So the obvious solution would be the move the mic further from the cabinet, and that does solve the issues above, with the exception of the floor reflections. But... as you'd probably expect, micing a cabinet from a distance introduces reverberation from the room which has its own issues. Enter reflection-free far-field impulse responses.

Simply put, taking an FFIR involves three things:
  • Moving the microphone further away from the cabinet, eliminating the first three problems discussed above.
  • Placing the microphone on the floor so any reflections from the floor only affect very high frequencies that don't matter for our purposes.
  • Using a short impulse and a large space so that the entire impulse reaches the microphone before any reflections from the room can.
The result is a 'pure' capture of the sound of the cabinet in its entirety and with none of the room. The benefits being:
  • It is a truer representation of the way the cabinet sounds.
  • Which in turn means when it's played through FRFR speakers it sounds more like a cabinet in the room.
  • A sound that usually doesn't require high and low cuts that most of us routinely apply to close-miced cabinets.
Jay Mitchell is the biggest force behind reflection-free FFIRs (I want to say he came up with the idea, at least for modelling, but I might be wrong) and he has a long and fascinating threat over at TGP called IR Properties. It's worth a read if you want to understand it deeper.
 

peteri

Inspired
Stupid question of the day - would the best way to record these not be in one of these 'dead' rooms the microphone manufacturers use? I.e. completely sealed and reflection free
 

Corinthian

Regular
Stupid question of the day - would the best way to record these not be in one of these 'dead' rooms the microphone manufacturers use? I.e. completely sealed and reflection free
For impulse responses, no, not really. Anechoic chambers are never completely anechoic and they aren’t necessary if you have a sufficiently large and quiet space.
 

FractalAudio

Administrator
Fractal Audio Systems
Moderator
Here's a simple, if a little long-winded, explanation:

The premise is that close micing a cab is problematic (from a technical standpoint at least... you might like the sound and it's what engineers have been using for years) for a few reasons:
  • Speaker cabinets produce sound from more than just the speaker and when you listen to a real cab in a room you're hearing the sound coming from the cab as a whole, not just the speaker. Close micing picks up very little of the sound from elsewhere because the mic is close to the speaker.
  • If the cabinet has multiple speakers the mic only picks up sound from one.
  • Many mics exhibit proximity effects increasing the bass response when they are close to the sound source.
  • The sound from the speaker bounces off the floor causing peaks and nuls in the waveform because of phasing (meaning that some frequencies are pronounced and others too quiet in an unnatural way.
So the obvious solution would be the move the mic further from the cabinet, and that does solve the issues above, with the exception of the floor reflections. But... as you'd probably expect, micing a cabinet from a distance introduces reverberation from the room which has its own issues. Enter reflection-free far-field impulse responses.

Simply put, taking an FFIR involves three things:
  • Moving the microphone further away from the cabinet, eliminating the first three problems discussed above.
  • Placing the microphone on the floor so any reflections from the floor only affect very high frequencies that don't matter for our purposes.
  • Using a short impulse and a large space so that the entire impulse reaches the microphone before any reflections from the room can.
The result is a 'pure' capture of the sound of the cabinet in its entirety and with none of the room. The benefits being:
  • It is a truer representation of the way the cabinet sounds.
  • Which in turn means when it's played through FRFR speakers it sounds more like a cabinet in the room.
  • A sound that usually doesn't require high and low cuts that most of us routinely apply to close-miced cabinets.
Jay Mitchell is the biggest force behind reflection-free FFIRs (I want to say he came up with the idea, at least for modelling, but I might be wrong) and he has a long and fascinating threat over at TGP called IR Properties. It's worth a read if you want to understand it deeper.
1. Close-micing a cabinet is not problematic. It's been done for years and solves a lot of technical issues. It may sound different than listening to that cabinet at distance but it's no more right or wrong than any other micing technique.

2. Far-field has nothing to do with the picking up the sound from multiple speakers and "hearing the sound of the cab as a whole". Many cabinets have only one speaker. The far field of an acoustic radiator (i.e. speaker) is the point where the sound waves coming from the speaker behave as though the radiator is a point source. In the far field the intensity falls off by the inverse square of the distance.

At distances less than the Fraunhofer distance the field is characterized by widely varying intensity due to interference. To calculate near field beam patterns you can treat the transducer as a lot of smaller point sources and find the contribution of each point source at a given point. As you move around in the near field each point source has a different phase and intensity due to distance and angle. This interference causes the intensity to vary widely as you move around.

3. You can measure the far field response of a speaker in a number of ways. One way is a free field measurement. The speaker and mic are suspended far above the ground so that the multipath from the ground occurs after the direct path IR has decayed fully. This is obviously difficult.

Another way is using a ground plane measurement. The microphone is placed on a smooth hard surface either outside or in a large enough room so that any reflections occur after the direct path IR has decayed. Placing the mic on the floor effectively removes the floor reflection as the direct path and reflected path are the same.

4. There is no such thing as a "short impulse". An impulse is, by definition, infinitely short. Regardless, impulses are almost never used to measure IRs. Almost everyone uses sine sweeps or other wideband waveforms (PRN sequences, etc.). The length of the sweep does not need to be short and, in fact, can be quite long. The longer the sweep the better the SNR.

5. A far-field IR is not a "truer" representation. It is simply the response of the cabinet in the far field. A near field IR is equally "true", it just sounds different. Far field IRs are not a panacea either. They're difficult to obtain for speakers with multiple drivers, i.e. 2x12, 4x12 because the far field is extremely far away. At 10 kHz the far field for a 4x12 is something like 100 ft. (too lazy to do the math right now).

When we listen to multiple driver speakers we are typically in the Fresnel zone. If you take an IR of a multiple driver speaker in the Fresnel zone there will be deep notches in the spectrum due to the different path length of each driver. We don't hear this though because we have two ears and our aural processing averages things out.
 

Moeed Kazi

Inspired
Here's a simple, if a little long-winded, explanation:

The premise is that close micing a cab is problematic (from a technical standpoint at least... you might like the sound and it's what engineers have been using for years) for a few reasons:
  • Speaker cabinets produce sound from more than just the speaker and when you listen to a real cab in a room you're hearing the sound coming from the cab as a whole, not just the speaker. Close micing picks up very little of the sound from elsewhere because the mic is close to the speaker.
  • If the cabinet has multiple speakers the mic only picks up sound from one.
  • Many mics exhibit proximity effects increasing the bass response when they are close to the sound source.
  • The sound from the speaker bounces off the floor causing peaks and nuls in the waveform because of phasing (meaning that some frequencies are pronounced and others too quiet in an unnatural way.
So the obvious solution would be the move the mic further from the cabinet, and that does solve the issues above, with the exception of the floor reflections. But... as you'd probably expect, micing a cabinet from a distance introduces reverberation from the room which has its own issues. Enter reflection-free far-field impulse responses.

Simply put, taking an FFIR involves three things:
  • Moving the microphone further away from the cabinet, eliminating the first three problems discussed above.
  • Placing the microphone on the floor so any reflections from the floor only affect very high frequencies that don't matter for our purposes.
  • Using a short impulse and a large space so that the entire impulse reaches the microphone before any reflections from the room can.
The result is a 'pure' capture of the sound of the cabinet in its entirety and with none of the room. The benefits being:
  • It is a truer representation of the way the cabinet sounds.
  • Which in turn means when it's played through FRFR speakers it sounds more like a cabinet in the room.
  • A sound that usually doesn't require high and low cuts that most of us routinely apply to close-miced cabinets.
Jay Mitchell is the biggest force behind reflection-free FFIRs (I want to say he came up with the idea, at least for modelling, but I might be wrong) and he has a long and fascinating threat over at TGP called IR Properties. It's worth a read if you want to understand it deeper.
Thanks Mate for taking out the time to explain this, I really appreciate your help.

Makes more sense to me now, when I understand it well.

Thanks once again.
 
The hard part is defining the problem.
Apparently, we're trying to get speaker B (the FRFR speaker) to act like speaker A (the original speaker).
If the two speakers have different radiation patterns (and they probably do), then it's not possible to do it exactly.
So what do we want to preserve ?
The power response ?
The on-axis frequency response ?
Something else ?
 

666was999

Forum Addict
There's these guys that aim their knees from behind with their guitar cabs. Because they stand way off-axis they have to compensate for missing highs, so they crank them up on the amp. Then they move around in front of their amp until they find a place where they like what they hear, their sweet spot.

Since everybody has a different sweet spot, it's hard to define what that actually is. It's even more chaos when they move around in front of their cab since the sound constantly changes then. Some might even move to different positions when they switch channels to find the best sound instead of tweaking the amp controls.

I wonder if FF-IRs can substitue all of that.
For the different sweet spots you'd need different off-axis IRs...so far that's doable.
But how do you emulate moving around in front of the cab? Maybe we'd need some IRs from different positions that constantly morph from one to another? Adding comb filter triggered by an LFO? A comb filter triggered by a GPS sensor and a compass? Yeah, that'll do the trick.

I have a different suggestion. Aiming at your knees with a cab and moving around until a bad sound starts to please you was wrong. Get over it. Get used to the sound that the audience is used to. It can't be that bad when the audience loves it.
 

shatteredsquare

Forum Addict
compliments to the mic placement chief, these are by far the clearest, crispest, smoothest, most detailed IRs i have ever heard or paid for, even the stupid dark ones are all in phase to let the highs through to still be usable...how do they do it?? Not having much luck mixing them with anything, the comb filtering turns it all into mush, but by themselves I've never heard anything so clear.

When are the Factory IRs going to come out as Non-MPT? These sounds amazing!
 

mikeyg

Inspired
Is there anything additional required in the IR capture process for an open back cab? Micing front and back?

When I tried my first FFIR I immediately noticed the punch and pop that I was missing from my favorite 2x12 Celly Blue open back cab. My axe 3 is waiting unopened at home, and the first thing I am trying is these FFIRs!
 

666was999

Forum Addict
Is there anything additional required in the IR capture process for an open back cab? Micing front and back?

When I tried my first FFIR I immediately noticed the punch and pop that I was missing from my favorite 2x12 Celly Blue open back cab. My axe 3 is waiting unopened at home, and the first thing I am trying is these FFIRs!
You can capture the frequencies of your open back cab and use any FRFR cab to display them. But it will not punch and sound the same. You can't capture the way an open back cab spreads it's sound in the room.

When you prefer 2x12" open back cabs get an 2x12" open back FRFR cab, that might be the closest you can come to it using IRs. Don't use such an FRFR to tweak DI signals for the FOH...the open backs don't display the lows flat enough.
 
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