Impulse Response discussion

[DrNewcenstein]

Ok, so I've upgraded my Digitech 1101 to vC63, which includes user-made cab options (IRs).

I looked around for some freebie IRs but didn't really know what to get, so I got a set made by a guy named GuitarHack.


Then I found a tutorial on how to make your own, which was quite interesting.

I know there are some companies selling theirs, and yes they're reasonably-priced and I'm sure they're great (Redwirez, etc).


So, looking at the ones from GH, he's done several in each series with various mic placements and even different tubes in the amp. I'm not entirely sure what head/cabinet/mic he used (found the download link from another forum without all the background info).

Anyway, noticing they were all simply wav files of a very short "blip", I loaded a few in XEdit to check them out in the 1101. Still not sure what I'm "seeing" with these, other than what amounts to EQ "effects".

Then I got the bright idea to convert some random wav files for use as IRs.

One of them was a snare hit from BFD2's sample library.
Another was the first thing you hear in Master Of Puppets (everything hitting at once).
Then I loaded a voice sample from Oblivion (yes, the game), and then a sound effect from it.


Tinkering with those yielded results, but nothing where you'd go "hey, that sounds like a Greenback-loaded 2x12 Vintage Fender", etc (then again, it's not like I have one lying around to compare to, so....)


Anyway, I went back to the tutorial I found, which at first read like stereo instructions, and re-read it until I had a more firm grasp of what to do.

Basically you generate a tone (Audition 3 has a built-in Tone Generator - A440Hz, etc etc), then pump it into a power amp+cabinet and record that with a mic, then run another copy of the tone through a software sim (he used Amplitube) with a Clean patch, then something-something-and-so-forth with it... I forget the rest.
It's here if you want to read it:
http://www.guitarampmodeling.com/viewtopic.php?f=32&t=1745&sid=283209b37a9f6b2acbf00b9bad1957d4

So I did a little of that: generated a tone, ran it through a vst of some sort, then ran another copy through another vst, etc etc, then put them both in a multitrack session and mixed them down to one file and used that as the IR.

Interesting results, but again, I can't say if it's related to a real-world cabinet or not.


However, one thing I've always been interested in is these Frequency Response charts you see with almost every piece of gear (cabinets, speakers, mics, heads, etc).
Like these:
http://www.bing.com/images/search?q=frequency+response+chart&qpvt=frequency+response+chart&FORM=IGRE

One thing in particular I've always wanted to do was gather a bunch of them and try to "model" them with EQ (whether in a rack unit or as an EQ preset in Audition), but wasn't quite sure how to go about it.


Until now.


Would I be correct in assuming that these charts are compiled by running a generated test tone through a given item (cabinet, speaker, out of known frfr speakers into a mic, etc) and then measuring the frequency response?

If that's the case, I'm also assuming they pump a full range of tones from 20Hz to 20kHz to measure the response along the spectrum?

If that's the case, then theoretically one should be able to take an existing Frequency Response Chart for a given item and generate a series of tones from 20Hz to 20kHz and tweak an EQ patch to replicate the response chart, and use that for an IR, and thus get an accurate representation of said piece of equipment.

Agree? Disagree?

 

[Warheart]

Re: Impulse Response discussion

on www.redwirez.com they have a sample Marshall 1960A with Celstion G12M's you can download for free to try.

Also, the more samples the better supposedly. I think the GSP only uses 128 or 256 samples per IR.

There are some cabinet IR companies(OwnHammer?) that are doing like 5512 samples and what not. In the case of that you might need software or an Axe-FX to take use of it.

 

[DrNewcenstein]

Re: Impulse Response discussion

I went to Redwirez but didn't see the link for free stuff. I did see that freebie link from another site but it was "email for link to the freebie". I'm not into it.

 

[Warheart]

Re: Impulse Response discussion

...Still not sure what I'm "seeing" with these, other than what amounts to EQ "effects".

If that's the case, then theoretically one should be able to take an existing Frequency Response Chart for a given item and generate a series of tones from 20Hz to 20kHz and tweak an EQ patch to replicate the response chart, and use that for an IR, and thus get an accurate representation of said piece of equipment.

Agree? Disagree?

I agree, but I think its a case of different EQ curves stacked.

IMO it comes down to four factors:
1. Amp model, and what frequencies the tonestack is EQ'd for.
2. Speaker model
3. Microphone model
4. Microphone position.

All of these affect the overall EQ shape.

That is a lot of variables, and I don't think you can replicate that with a simple 31 band EQ.

I liken it to changing pickups in your guitar cause one pickup is too scooped or what not. Regardless of turning up the mids on the amp, you can't get it to not sound like that.

I don't think that running a scooped pickup into a mid heavy amp is the same as running a mid heavy pickup into a scooped amp.

 

[dominus]

Re: Impulse Response discussion

I went to Redwirez but didn't see the link for free stuff. I did see that freebie link from another site but it was "email for link to the freebie". I'm not into it.

http://www.redwirez.com/free1960g12m25s.jsp

You do have to put your E-Mail address in.

I did, and I think I've gotten one E-Mail from them since then.

I bought the Recabinet IRs when they were IRs and $15 or something. Downloaded every free one I could find too.

I don't care where they came from, or what cabinet they are, as long as I get a good sound. Right now I'm using some Mesa 2x12 IR that fits my style just fine.

Here's some more free Mesa ones:

http://signalsaudio.com/index.php?option=com_content&view=category&layout=blog&id=8&Itemid=21

 

[wahwah]

Re: Impulse Response discussion

The difference between the Redwirez IRs and some of the freebies like the GuitarHack stuff is the equipment and room they're using to record their IRs. The Redwirez guys really seem to know what they're doing, not only with their speaker and cab selections, but with the range of mics they have chosen. Where else are you going to get your hands on a Neumann U67 that's already been placed at various points around a bunch of different cabs and speakers? Or to be able to switch straight from that to a Royer 121, AKG C414, Neumann U87, U47, Coles 4038, etc. We're talking about a $50,000 + mic kit there alone. Add to that the fact that they are then using Prism AD/DA converters and Neve 1073 preamps to capture their samples, not to mention a great sounding room, and it's no wonder their stuff sounds so good.

The notion that you could replicate those results by studying frequency response curves with a white noise generator and fiddling around with a third octave graphic equalizer, is akin to entering a Fiat 500 in a Formula One race on the principle that it has wheels and an engine.

The problem you might have is with the limited number of samples available for IRs in your unit. This will effectively strip the Redwirez IRs of their room reflections, which may be ok for the closest mic'ing positions, but will drastically truncate any that have more room sound in them. According to aleclee's information, the Axe-Fx II has just doubled the number of available samples for user's cab IRs from 1024 to 2048, and it would have been for this reason.

I've applied the Redwirez IRs to quite a few different software modelers, including those in Logic, Revalver Mk III.V, Amplitube Fender and LePou (which don't have cab sims to start with), and they have improved the results without fail, every time. The ability to change a cabinet, mic or mic position at mixdown by simply changing the IR in a convolution plugin is worth every cent of the small amount they are charging for the meticulous work they've done.



Cheers........................................ wahwah

 

[DrNewcenstein]

Re: Impulse Response discussion

http://irlibrary.org/index.php?cat=microphones

 

[dominus]

Re: Impulse Response discussion

I've applied the Redwirez IRs to quite a few different software modelers, including those in Logic, Revalver Mk III.V, Amplitube Fender and LePou (which don't have cab sims to start with), and they have improved the results without fail, every time. The ability to change a cabinet, mic or mic position at mixdown by simply changing the IR in a convolution plugin is worth every cent of the small amount they are charging for the meticulous work they've done.

That right there sums it up. The amp sims all seem to be the same boxy sounding lackluster simulator until you try some 3rd party cab IRs and then they open right up.

 

[wahwah]

Re: Impulse Response discussion

http://irlibrary.org/index.php?cat=microphones

Yep. There's some IRs of three different condenser microphones. I'm not sure of the relevance of your link to this discussion, unless you intend getting IRs of a cabinet captured with one microphone, and running them through IRs of a different microphone. Which would be kinda odd. Especially when there are already great IRs available that capture the three vital elements, speaker, cab and microphone, all in the one IR. 4 vital elements including the room, if you use an IR of a mic set back from the cab.

The beauty of the better IR producers is that they have chosen microphones renowned for being great on guitar and bass cabs. The best of the ribbon, condenser and dynamic mics that are commonly used on cabinets by the vast majority of producers. The Redwirez IRs come with combinations of...

AKG C414B-ULS
Audix i5
Beyerdynamic M160
Coles 4038
Neumann U47
Neumann KM84
Neumann M8/CMV563
Neumann M7/CMV563
Neumann U87
Neumann U67
Royer R121
Sennheiser MD421N
Sennheiser MD441
Sennheiser MD409
Shure SM7
Shure SM57
TAB-Funkenwerk SM57
Electrovoice RE20
Earthworks TC30/M50
Lawson L47
Blue Bottle/B4 (Room only)
Blue Bottle/M7
Heil PR30

That's some serious mic kit. Combine that with a serious collection of great speakers and cabinets, a great room, first class signal path and AD/DA conversion, and the picture emerges. What an amazing resource.




Cheers.......................................... wahwah

 

[DrNewcenstein]

Re: Impulse Response discussion

Some of those at IRlibrary work well with the 1101, though they do require some manual editing (cut off the leading silence, convert to stereo) but they load just fine. I like the Plexi 57 offaxis better than what comes with the 1101.

Haven't tried using them in Audition yet.


Maybe when I get that big pro studio gig I'll go for the big pro studio IRs, but as of right mow, as far as I'm concerned, most folks won't know the difference once it's all mixed.