help on impulses and convolution

[fliffo]

I'm new to impulses and convolution and I'm just starting to be familiar with this concept.
One thing I don't understand is this:
There are different plugins that can load and apply impulses, so we have reverbs (like SIR, altiverb), amplifiers (like voxengo boogex). They seem "specialized" for a task (reverberation, distortion etc) BUT on the other hand you can get an impulse from virtually any hardware audio device on earth (an effect unit, a compressor, a preamp, a mic etc...) So why there are such "specialized" plugins instead of just a generic one that simply loads impulses (no matter their nature) and makes the convolution thing?
What appens if, for istance, I load a reverb impulse into an amplifier plugin? Or a compressor impulse into a reverb plugin?

[TechNoiZ]

[greendoor]

Try it and see! You are right, in that you can put any impulse into these. You can even use wave files that were never intended to be an impulse, and get really strange effects. Two things to consider - you need to be very aware of the difference bettween Insert and Send effects. An Insert effect is where you process the whole signal, and use the 100% wet output of the effect. Usually, distortion, EQ, compression etc are Insert effects (maybe called Channel or Pipeline or Signal Processing). The other type of effect is a Send effect (maybe called layering or sound-on-sound), where the effect creates a 100% wet sound that you then mix over the top of your original dry sound.

Some of the convolution impulse processors allow you to mix Dry and Wet. Others, like the Voxengo AF Impulse and Boogex, are purely Wet. The Boogex, being a guitar amp sim, has distortion and eq designed for guitar, so probably not ideal for normal reverb apps - but try it and see. Just be aware of what type of impulse you have, and whether you need to mix wet and dry, or not.

[fliffo]

ok, agree with the dry/wet point
...but i'm afraid of this:
Let's say I have a wonderfull impulse of an old good vintage chorus unit someone gave me, where do i load this one? If I load it into (let's say) Voxengo boogex will it apply any colouring to the original unit sound due to the fact that
"being a guitar amp sim, has distortion and eq designed for guitar"?
Around I've seen many kind of impulses from many kind of audio equipment (also microphones) but on the other hand just convolution-reverbs/amplifiers plugins...what about those non-reverb or non-cabinet impulses? Where to use them? Are they usable into convolution-reverbs/amplifiers plugins without colouring the original sound?

[greendoor]

There are plenty of 'generic ones' - so just use them. The aren't just suitable for reverb. Boogex is a guitar amp sim, so unless you want a guitar amp sim - don't use it. I think using a cabinet impulse is ideal for DI guitar, so it's a brilliant feature for a guitar amp sim. SIR is a good choice for any type of impulse. Just remember to turn off the dry sound for your pipeline impulses. I believe a vintage chorus impulse would probably be a pipeline one - so turn off the dry sound. (I could be wrong there - depends on the unit and how it was samples).

[fliffo]

Ok...that's what I needed to know, Thanks greendoor.

[dburgan]

Let's say I have a wonderfull impulse of an old good vintage chorus unit someone gave me, where do i load this one?

Typically, plugins that are marketed as convolution 'reverbs' are really just generic convolution engines. Plugins like SIR and Convo Boy and Pristine Space load WAV files directly. Other plugins can 'import' WAV files, and once imported they'll do the same as SIR, etc. So check those out.

A word of warning: convolution is time-invariant. That means that any process that is time-variant (e.g. compression, etc.) will not be accurately modeled by recording an impulse response of the process. So you probably will not get the results you intend by loading a 'vintage chorus' impulse response. Most likely you'll get something that approximates the EQ change the vintage chorus imposed on the signal along with some kind of weird digital modulation artifacts.

But that said - definitely give it a try. The result may not sound like vintage chorus, but it very well may be interesting in its own right!

[fliffo]

thanks for the good infos!

[Midiworks]

Distortion, compressors, modulations can NOT be captured.
For a compressor you would just get the caracter of the unit,
not the compression.

[Rangtangtang]

But some of them come installed whith the unit to protect against theft. Like those tube and amp emulation ones. I assume that those types of impulses are very small, compared to reverb.

Latency is an important consideration, it depends if you think its more important to have real-time use or quality.

[Midiworks]

Theft ?
Simply send a spike through it and record the output,
bingo, you just created a new impulse response.

Senseless to start a wrong/right discussion.