How to create an impulse

Speaker Cabinet Impulses

How to create an impulse

Postby Alu » Sat Sep 29, 2007 10:39 am

Ok guys, it seems pretty simple... it took me a few minutes to understand it, and I've tested the method "impulsing" an amplitube 2 cab... it works!

So just download Voxengo Deconvolver:
http://www.voxengo.com/product/deconvolver/

The demo version works perfectly for what we have to do, so you don't need to have a registered version (but the demo will allow you to create 3 impulses per session, so, after 3 impulses, you have to restart the program :) )

Open Voxengo Deconvolver.

We need a "TEST TONE", basically a sine sweep containing al the frequencies we can hear... just click on "Test Tone Gen", use the default settings (24bit, 44100Hz (or superior, best is 96000Hz), mono,12 sec., DON'T CHECK "apply fade in-out for reverse" ) and click on "generate".

Create an impulse response from a real gear

Ok, now we need to route that wave file inside the Cab/Mic we want to capture... so you have to route the file inside the power amp of your head (fx-return or power-amp in) and record the cab output with the mic...
Just connect your soundcard output to the poweramp and record the mic signal (you could need 2 pc or a soundcard that allows you to play and record at the same time... you could do that with a DAW). Beware the clipping of the Test Tone!!! It doesn't have to clip!!! Lower the volume!!!

Create an impulse response from a software sim

It's more or less the same thing, just easier!
We need to open our DAW and create a mono track, then load the Test Tone on it.
Now we have to open the VST from which we want to take the impulse response in the track insert, for example GR.
Now we have to close or bypass all the components we don't need (stomps, amps...) and activate only the cab+mic section.
Play the Tone Test now to see if it clips inside our VST. If so, lower the volume or use the "learn" function!
What we hear when we click "play" is just the Tone Test processed by the VST, and this is what we need, so export the file into a .wav file!

For both, then...

Obviously, if you have created a 96KHz test tone, you have to record at the same sample-rate!!!

Export the recorded tone on a 24bit Wave Mono file.
IMPORTANT: when you export, remember to add a bit of silence at the end of the clip you're about to export!!!


The recorded tone will be the "file to process" in Voxengo (obviously the Test Tone File is the Test Tone we have generated a while ago, so the original 12 s sinesweep).

Set "Out Bit Depth" to 24 and select just "Normalize to -0.3dbFS".
You could also check the "MP Transform" option (the manual says that gives more realistic results)

Click process and you'll have a wave file in the same directory of the processed tone.
This is your impulse!

(probably you'll have to tweak the volumes to get the impulse right... so, try, try, try!)

Hope it helps!

For any question, just ask, I'll try to help you!
Last edited by Alu on Tue Jan 08, 2008 8:45 am, edited 3 times in total.
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Postby Tjongan » Mon Oct 01, 2007 4:48 pm

Sweet, thanks for the guide!

Im gonna try this out just for fun..when I see my good old speaker cab again :cry:
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Postby ARIBAI » Mon Oct 01, 2007 6:47 pm

hey alu... very interesting thread!

when you say "record the cab output with the mic" you mean WHILE PLAYIN´A RIFF??

if so: does volume level make any difference? (from the amp that is)
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Postby Alu » Mon Oct 01, 2007 6:58 pm

ARIBAI wrote:
when you say "record the cab output with the mic" you mean WHILE PLAYIN´A RIFF??

No man! I mean you have to send the Test Tone inside the amp and record the output! The output will be the test tone processed by the cab and mic!

Understood?

ARIBAI wrote:if so: does volume level make any difference? (from the amp that is)

Well I don't know... the volume could drive the power amp (fx-return or power-amp in input), but impulse won't capture the distortion...
Is important that the signal recorded from the mic doesn't clip!
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Postby Tjongan » Mon Oct 01, 2007 9:06 pm

I guess the elements works harder and therefore sound better with more volume? as long as it dont clip ofcourse.
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Postby EasySleazy » Mon Oct 01, 2007 9:12 pm

I think GuitarHack had a thorough explanation for all of this stuff when he posted his impulses at Sneap's forum.
ffffffffff
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Postby Alu » Mon Oct 01, 2007 9:53 pm

Tjongan wrote:I guess the elements works harder and therefore sound better with more volume? as long as it dont clip ofcourse.

I guess you should have less attenuation, so more low-end and more definition... just try different settings and see how it changes...
Remember that in many amps, the presence knob acts after the fx-return, so it will affect the overall eq!
The normal tonestack (low,mid,treble) instead, is in the preamp section, so, using the fx-return or power-amp in, it should be uneffective (always depending on the circuit, there could be some rare exceptions)
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Postby hockeyguy88 » Sat Oct 20, 2007 7:04 pm

Excellent tutorial... Should probably have the post stickied so it's easy to find down the road
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Postby Alu » Thu Oct 25, 2007 12:28 pm

Updated with infos about gettina an impulse from a software sim!
Check the first post!

Can someone sticky this?
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Postby asynd » Thu Oct 25, 2007 9:30 pm

eeh just tried again and still had the same warbly effect in the impulse

am i supposed to run the single directly into the cab and not go thru the amp?
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Postby Alu » Fri Oct 26, 2007 10:57 am

If you don't use the power amp, your signal will be to "weak" to push the speakers, so it will not work!

Did you check if there is something clipping in your chain? Maybe the mic-preamp?

Can you upload the warbly impulse please? I want to check it out!
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Postby asynd » Sat Oct 27, 2007 2:01 am

yea i lowered the volume of it, still not all sure what im doing wrong lol

http://www.esnips.com/doc/6b9dc119-a0e8 ... mptes1t_dc


hmm ive noticed i get Audio dropout soon as i load the impulses that ive made too, sometimes it happens but with the recent one i made soon as i hit start, audio drops :/
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Postby Alu » Sat Oct 27, 2007 10:05 am

:shock:
WTF is that?

Really strange man, expecially if you compare the signal with the other impulses...
Sounds like a fast sweep...
There is something wrong...

When you export the cab+mic processed Test Tone, check if it starts at 0, like the original Test Tone! I mean that there must be silence at the end of the processed Test Tone but not at the beginning (I think...)

Can you share the processed Test Tone that you use to deconvolve?
I could try to deconvolve it!

EDIT: I've just noticed that the impulse is 48.000Hz! Remember that the test tone is 44.100, so use always 44.100 as bitrate in your project!
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Postby asynd » Sun Oct 28, 2007 9:58 am

hmm, ive noticed that my cpu usage jumps to 90% or more when i load the ones i made :/


[url]this is the sweep tone it generated
http://www.esnips.com/doc/2a5ce686-fae5 ... -24-M-3.0s[/url]

and yea i have been recording a few seconds after the tone goes thru the amp
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Postby Alu » Sun Oct 28, 2007 11:05 am

Sorry man, you misunderstood me...

I mean the Test Tone PROCESSED by the cab+mic! This is the one automatically generated by Voxengo, right?

So you run this .wav file inside your fx-return and record the output from the cab with the mic... right? I want the recorded one!

Thanx for the effort man! I know it's boring...
Keep it up
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Postby asynd » Mon Oct 29, 2007 4:01 am

oh haha. i was wondering why you would want that tone haha.

http://www.esnips.com/doc/36840d36-56ac ... 6/imptes1t
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Postby Alu » Mon Oct 29, 2007 8:20 pm

Ok man, found the problem!
Use ALWAYS 44.100 Hz as your recording bitrate if you use a 44.100 Hz tone test! If you use different bitrates the lenght of the tones (the Test one and the recorded one) will be different and the deconvolution will be "strange".

When you open your DAW, create a new project, set 44.100 as bitrate, then record the signal!

I've tweaked your processed tone and finally got the right lenght with the right bitrate and this is the resulting impulse...
It sounds a bit fizzy and a bit hollow on the lows and mid-lows, but it sounds ok... just download and try it
http://www.esnips.com/doc/32991ecd-b9a7 ... yndImpulse

The things I've done to make it right could have changed something, so this impulse could be not "true" and that's why it sounds ok but not that good...

So man, remember to use always the same bitrate!

Keep it up man!

Thank you!
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Postby asynd » Tue Oct 30, 2007 12:42 am

ah ok

here are two i just recorded using different volumes on the output of the sweep. trying to figure out how much of a difference the output of the sweep effects the impulse

first one is -12db.
http://www.esnips.com/doc/7b1a6b9e-2082 ... mptest2_dc

second is -3db.
http://www.esnips.com/doc/26108311-772b ... 058/3db_dc


its just a center mic position on the topright speaker with the sm57
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Re: How to create an impulse

Postby ruisealman » Tue Jan 29, 2008 8:21 pm

This thread should get a sticky.

/sticky
/sticky

:D :D :D
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Re: How to create an impulse

Postby Jakerock_ » Sat Mar 15, 2008 4:59 pm

Hey all...
Been using impulses for awhile, but trying to capture stuff for the first time...
The most useful thing I could have right now would be an impulse from my Boss Octave pedal.
Its what it sounds like, a stomp box for guitar that outputs a lower note...
Image


Im getting terrible results, and am hoping that you all might have a clue as to what I am doing wrong here!
Thanks for reading this!

Heres what I am doing:

1.) I make a (24 bit) 12 second test tone with Voxengo Deconvolver

2.) Import it into my DAW, and record it thru the pedal to another track (starting @ 0:00), leaving silence @ end
Image

3.) Export the recorded octave sweep (24bit), and process it with Voxengo Deconvolver, using these settings
Image

The file that Voxengo gives me is very short (bottom waveform)...
Image

The resulting convoloution, when applied to a previously recorded DI guitar track with S.I.R. is a quieter, seemingly non effected signal, with a ghost of a delay on it...

Heres the results
D.I. guitar Uneffected
http://shup.com/Shup/29779/TELE_RAW.mp3

Same guitar, playing the impulse back thru S.I.R.
http://shup.com/Shup/29780/TELE_SIR_AND_IMPULSE.mp3

Here are the wav's:
test tone: http://shup.com/Shup/29785/TESTTONE.wav
recorded thru octave pedal: http://shup.com/Shup/29787/THRUOCTAVE.wav
voxengo deconvolve output: http://shup.com/Shup/29789/record-sine_dc.wav

Here is a zip containing all the audio files above:
http://shup.com/Shup/29795/Jakerock_OctaveImpluseProblems.zip

Thank you very much for your time and insight into what I am doing wrong here!!!
-Jakerock
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Re: How to create an impulse

Postby Alu » Sun Mar 16, 2008 9:56 am

Seems all ok...
Try to check the MP Transform and Normalize button... sometimes the MP Transform is the only way to make things work...
Anyway, I've tried the MP Transform on your sweep, it doesn't change anything...
The recorded sweep seems distorted... lower the input signal that enters in the octave and try again.

I don't know if impulses can capture the sound of an octave pedal btw...
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Re: How to create an impulse

Postby Jakerock_ » Sun Mar 16, 2008 2:26 pm

Alu,
Thanks for you help on this!

Im getting the impression that the Octave just wont be convolved...
Something about the way it processes the lower note that doesnt jive with how impulses work...

The pedal tracks best with staccato playing, and theres nothing staccato about a 12 second sweep!

Which brings me to another question if you dont mind...

I have heard that there is an alternate signal to send thru non acoustic gear (compressors, etc...)
Something about a "one sample pulse" or something like that...
Anyone have any details about that, or know when this kind of signal is more appropriate than a sweep?

Super glad to have found this forum!
(Found it thru a Reaper forum post about guitar presets)
http://www.cockos.com/forum/forumdisplay.php?f=19

Thanks alot!


-Jakerock
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Re: How to create an impulse

Postby Alu » Sun Mar 16, 2008 2:29 pm

The simple pulse is a Dirac impulse... you could search it on the net, but I doubt it would work...
You can use all the signals as test-tone, but they should give you the same result...
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Released Plug-Ins: NRR-1 | TS-999 SubScreamer | The Anvil | SHB-1 | PTEq-1a | TSB-1 Tyrant Screamer
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Soundcard: M-Audio Profire 610
Monitors: ESI nEar 08 eXperience | AKG K141 Studio Headphones
Studio Software: Cubase 6 | Overloud BREVERB | PSP sQuad | Steven Slate Drums 3.5 Platinum | Toontrack SD2.0 | URS Channel Strip Pro | VescoFx Provoker | Voxengo Curve Eq | Voxengo Elephant 3
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Re: How to create an impulse

Postby Jakerock_ » Sun Mar 16, 2008 2:39 pm

Thanks again Alu!

Yeah, I dont think that the other type of "short burst" signal will work either...
But still wondering if there are situations where this is the best signal to use?

-Jake
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Re: How to create an impulse

Postby Jakerock_ » Sun Mar 16, 2008 2:44 pm

"Here we're talking only about some time invariant FX like Reverb and Delay. Dynamics, Pitch Shifter and modulation FX in general won't work. That means you can capture something, but when applied, the result sounds different than the original."
from http://www.noisetime.com/impulsecreation.html

That makes sense, considering my results with the octave pedal...
But I have heard some compressor impulses that seem to do what they advertise...
Although I dont have the real gear to A/B...

Is is generally considered impossible to capture a compressor?
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