View Full Version : Impulse files - how-to?

07-05-2002, 09:50 AM
Impulse files are new to me, so I hope somebody can enlighten me about the best way to use them. I was able to work with them enough to see that they\'ll be very useful indeed - I got a very good effect without any of the strange artifacts that I sometimes hear in regular software reverbs. But I\'m pretty sure I\'m not using the impulse files correctly, so....

First, some general questions. Should the impulse files be applied after all other effects? I\'d assume so, since it\'s such a \"global\" change, but maybe there are things that would make sense to do afterwards.

Should impulse files be applied to the completely-mixed wav, or to the parts, or both? My assumption is that you\'d use something like Cakewalk\'s soundstage plugin to place instruments at various points in the room, then use an impulse file to put the players in a big hall.

Finally, Cool Edit Pro is the only program I have that knows what to do with these things, but I don\'t think I\'m using it right. I load in one of the impulse .wav files, then go to Transform|Special|Convolution. I click \"Add Sel\", which lets me turn the wav into a .imp file. That all works, but if I apply the resulting .imp to some other wav, the result is almost inaudible! On the \"Add Sel\" Dialog, I can change the Global Setting for volume to 500% before saving, and then I get an audible (but still very quiet) result when I process another wav. If I mix this with the original dry wav, again pumping the volume way up on the processed file, I can get a very nice, natural sound. But this doesn\'t seem right at all - the impulse files that come with CEP don\'t produce such quiet results. There must be something I\'m doing wrong when converting the .wav to a .imp; either that or CEP is expecting the .wav file to be \"special\" somehow.

Any advice appreciated!

Tom Hopkins
07-05-2002, 08:41 PM

There are at least a couple of ways to use the impulse files. The most obvious way is to apply the impulse to the full stereo mix, adjusting the wet/dry ratio to taste.

It is also possible to mix section by section, placing each instrumental section in its desired position on the stereo stage and then processing that section with the impulse file. I suggest you not write the impulse processing to the section file itself, instead . . . write each “all wet” version to a separate stereo file that can be mixed, in level, like a reverb “return.” Also, I’ve had better results creating the “all wet” impulse file from a summed mono version for sections that are greatly panned. Keep the file stereo but with identical summed left and right channels. This way sections with instruments drastically panned to one side will return acoustic “reflections” from all points across the entire stereo stage, rather than favoring the side to which the instruments are panned. By having separate “return” files for each section you have considerably more control over layering your soundstage. This can give a more detailed impression of variations in the depth of field compared to a single application for the entire mix.

If you use Cakewalk’s Soundstage I recommend that you use somewhat higher settings for “absorption” and “trapping.” This lets Soundstage control the instrumental positioning while the impulse files supply most of the (more natural-sounding) reverb tail.

Since I use SoundForge’s Acoustic Mirror to apply the impulse files, someone else will need to give you detailed suggestions for Cool Edit Pro.


07-05-2002, 10:02 PM
Thanks Tom! That\'s a *big* help. As for CEP, I learned a bit more about it - there\'s a \"scaling\" factor that you have to play around with. I\'m not sure exactly what it does, but smaller values make a louder result, so now I can get processed files at a reasonable volume.

This update is just amazing. So many things that I wanted, so many other things I didn\'t know I wanted, but now I couldn\'t live without! Thanks and kudos to Gary, Tom, and everybody else involved in the update.

07-06-2002, 12:28 AM
I have tyo say that these are some of the best impulses I\'ve ever heard.

I\'ve been a big fan of Acoustic modelor, and convolution, but have my problems with linear convolution as a whole.

However, these are the most fantastic I\'ve heard.

I\'ll be checkingou altiverb first hand soon and will be able to compare. And hopefull, if its algorithm is actually that much better, I\'l try these out in that.

*MANY* thanks to Gary and (ahem) whoever tweaked those impulses for us images/icons/smile.gif

Adam Frechette
07-15-2002, 06:16 AM
Oh that is what it is for eh, I was using Sf 5\'s acoustic mirror to produce special effects with different sfx I have made, well now I know it can be used in conjunction with soundstage I will need to try it out.