Convolution is the Next Big Thing

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stubbsonic
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Convolution is the Next Big Thing

Post by stubbsonic » Wed Aug 15, 2018 6:36 pm

Convolution processing is an obvious choice for effects processing. It is often used for reverb, but can also be used for speaker emulation, resonator simulation, amp sim and many other things. However, it is very processor intensive. The convolution process takes an input signal and "convolves" it with an "Impulse Response" (IR) which is usually a short audio file that in some sense, contains the "essence" of a vibrational system (like a hall, a speaker, an instrument resonator, etc.). Creating a "formal" IR involves sending a full spectrum signal sweep or burst into a sonic "process" (like a room, or speaker, or resonator, etc), and then if necessary applying some post-processing to make it into a single "click" with a "tail" but really any audio file can be used as an IR. The longer the IR, the more CPU muscle it requires.

I also don't know how much standard convolution is used in Zoom and other gear-- I suspect it is part of at least some modeling processes. It would be great to see a true convolution processor in a small to medium format stomp or multi-effect. However, I don't know if processors are up to it.

One of the limitations of convolution processing is that it can lack some of the dynamic response of the original. Some vibrational "systems" behave differently according to dynamics and other factors. An IR does contain all the possible frequency content, but only under one level condition. That's not to say that it doesn't work well. Convolution reverb is stunning, and very convincing. It acts dynamically-- but while the reverb itself changes level along with the input source level, it doesn't change character. Still it works well.

I don't know if what I'm hinting at would be called "Dynamic Convolution" but some kind of more advance process that takes input level into account.

An iPad can do convolution, so I suspect it wouldn't be impossible to see a proper standard convolution processor in a stomper, but probably not soon.

It hasn't really hit the mainstream as a processor, but I suspect it will. It is relatively new, but super versatile. Weird it hasn't caught on yet, but it will.

EDIT: I did just find a product by Logidy called EPSi, which looks interesting http://www.logidy.com
Last edited by stubbsonic on Thu Aug 16, 2018 3:33 pm, edited 1 time in total.
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stubbsonic
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Re: Convolution is the Next Big Thing

Post by stubbsonic » Thu Aug 16, 2018 10:00 am

If I understand correctly, the EPSi can be loaded with two different versions of the firmware. One version allows for longer IR files, up to 6 seconds (for longer reverbs) but the drawback is that there is more latency. The other firmware allows for low latency by only allowing shorter IRs of 1.5 seconds, like cab sims and room reverbs.

Ideally, it would be good to see a hybrid firmware that adjusts latency based on IR length, however, I can imagine they would have done that, if it was easy.
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stubbsonic
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Re: Convolution is the Next Big Thing

Post by stubbsonic » Fri Aug 17, 2018 11:27 am

Once again, it would seem that the iOS solution is most cost effective (if you already have an available iPad).

AltiSpace and Mobile Convolution are two that allow you to load IRs. The former has more tweakable parameters. I haven't run any tests yet to see how they run on low buffer (low latency) settings.

The one worrying thing is that neither app appears to have been updated in a while, and it's unclear if they are still actively supported.

Another interesting one is Fiddlicator, which is designed for short IRs, like those to convolve stringed instrument resonators or cabs. It's not been updated in a long time either. If I have time I might test that as well.
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