Freesound Forums

Impulsions for reverbs...

Started February 7th, 2007 · 6 replies · Latest reply by UncleSigmund 17 years, 9 months ago

Glaneur de sons

112 sounds

41 posts

17 years, 9 months ago

I don't know if it's the right place to post it, but...

Does anybody knows about impulsions for convolution reverbs ? You know, the "accoustic mirror" effect in Sound forge...

These programs use the sound of environnements. For example, a guy records a gunshot, or any type of short sound with most of the frequencies (20 Hz to 20 kHz), edits it, cut the original sound and keeps the reverberation. Then he loads this sound in the plugin and here it is, he can apply the reverberation of the place to any sound he has.

I searched the web for info, impulses, how-to's, and found some cool stuff (I'll add some links tomorrow), but does anyone of you knows more about it ?

I'd like, for example, to make the sound of somebody shouting outdoor, far away, and I was never able to have something convincing enough. Any ideas (please don't answer "record the guy shouting outdoor" :lol: ) ?

I tried to search for impulses here, and it appears there are some interesting stuff I'll try.

But maybe somebody could write an article about it (don't ask me : I'm as bad in English as in explaining stuff !) ? That type of sound might be really interesting !

HardPCM

0 sounds

215 posts

17 years, 9 months ago

First, sorry for my english too, I"m a french from Canada...

Ok, first convolution is an statistical method for create reverbs or eliminate reverb
but i know too that convolution can be used for filters too or other things.

Now there is somes mathematics. I think you already know this
but in statistic if we do convolutions of a sound of 44100 samples with
an inpulsion of 100 samples the result is about 44200 samples but the first 100
and the last 100 samples of the result are not good/valid (duh!!!) and the only
solution to solve this situation is to put 100 sample muted at the start and the end
of sound to process...

before, this is stupid, but in convulsion/electronics you must know that impulsions
by definitions are on/off states...

for instance create on sound forge a file named toto.wav 16bit mono 44100Hz,
with a time of exacly 88200 samples(2sec), mute it completely,
set the time mode to "Option/Status Format/Samples",
go in "Edit/Go to" and in position box put 0, now in the tool bar there is the "Pencil Tool"
and try to draw the sample (sample 0) to more higher you can and only samples 0
save it
now take/make a drum loop and apply the "Accoustic Mirroir" with the impulse file toto.wav
if you do correctly the job you will see that the sound dont change,
its stupid but very important for the next step

in fact an basic impulses file have an impulsion of len 1 at position 0

now draw another sample at position 44100(1sec) to the max and
redo the job,
now you will see that the first and the last 2sec of the result are normal but the rest
is changed (on this situation you should hear repetition on each 1sec)

if this don"t work just shoot/email/post me picture/SNDfile of your work...

I can recommend for you to read DSP books, because this is a long but usefull method to
learn about convolution. I"m a electronic student its more easy for me to understand but
i dont think you studie this so i can recommend to you to learn more about convolution...

For my experience, i do research on the net for DSP docs and
found less than I expexted so You must go on google in the section BOOK and search
somes DSP books, if you dont know google offer limited or full access to many
commercial books...

good job!

[ :evil: ]_[ hock: ]_[ :twisted: ]

digifishmusic

614 sounds

274 posts

17 years, 9 months ago

Glaneur de sons
I'd like, for example, to make the sound of somebody shouting outdoor, far away, and I was never able to have something convincing enough. Any ideas (please don't answer "record the guy shouting outdoor" :lol: ) ?

To make an impulse you need to record the sound of an impulse sound in the environment then trim off the impulse itself and record the reverb.

So take a starters pistol, or some pieces of wood (slap together)...and 'Crack Shhhhhhhhhhhhhhhh h h h ", save the "Shhhhhhhhhhhhhhhh h h h " as a wave file.

The distance would be adjusted by the relative mix of the source sound against the convolution reverb of the same sound.

Some good sites...

http://noisevault.com/index.php

http://www.xs4all.nl/~fokkie/IR.htm

...this looks like what you are after...

http://www.xs4all.nl/~fokkie/Files/forest.sit

but needs to be converted from .sit to something you can use.

digifish

Glaneur de sons

112 sounds

41 posts

17 years, 9 months ago

Thanks for your answers, that was all what I need !

And the guy from the Belle Province has a level of english good enough for me!

I still think that a website like freesound should definitively have a section about impulses (documentation, tags, etc.). This is exactly the ultimate kind of sounds : the sound print of any kind of space !

Wandering on the web, thanks, to your links, I found a really good and huge library of impulses here (the vss3/vss3_32bit.zip file). Exactly what I was looking for !

I'll try to make some impulses myself, and post them here.

Thanks again !