Creative convolution: share your impulse responses!

I was inspired by this post to start a thread about the many creative uses for convolution, beyond just the common uses of recording amplifiers and spaces to create realistic emulations. I think it would be fun and enlightening to share IR’s we’ve found or made and the approaches we took to making them.

Here’s a good example of what I would call unconvential use of IR:

My process of creating a good sounding IR I find is almost the opposite to a good sample.
Any resonant frequency or bass that would make a sample sound good makes a muddy IR with peaks that cause clipping. Noisy, washy sounds that sound really thin as a sample can sound really big when you run a synth through them as IR’s.

At the moment I enjoy making washy unrealistic reverbs and delays, often using filtered white noise with various envelopes applied to it, like an exponential attack to get a modern, more hifi version of those 80’s reverse reverbs.
Another thing I like doing is multitap delays where each tap has a different EQ profile, perhaps also with some diffusion.

Here are some I made:


How does everyone else here use convolution? As much as I enjoy these approaches, I would like to branch out in my use of these techniques.

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Great idea for a thread!

I have only used convolution for “amplifying” non-acoustic instruments so far or if I record something really too dry (which is better than my not-so-great room).

Would love to try out some more experimental IRs though. Right now, I’m mainly using the M4L Convolution Pro. Works great for the most part but it can be picky about which IRs it likes. Not really sure what the issue is.

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Do you know of a good tutorial for using the M4L Conv. pro or convolution in Ableton in general? I’ve not much experience with convolution other than flailing around in the dark and seeing what happens.

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I do not but could use one myself. I was able to successfully create a “handclap” IR of my living room that functions on Convolution Pro as it should. I think I used Audacity at one point to edit and get the right format. However, I downloaded some IRs from Rhett Shull’s YT and those did not import. No idea what the difference is.

EDIT: You made me curious so I poked around a little and found this from the original developer of the Ableton Convolution device.

http://www.alexanderjharker.co.uk/Software.html

EDIT: Also, there apparently is an IR Measurment Tool that is in my M4L devices that I never knew/realized was there. I made my IR the hard way it seems. This might prove to be much better. I believe it downloaded/installed when I installed the original device years and years ago. The stock IRs sound so good I just never ventured out to create my own because I’m a dummy.

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I have been playing with Mungo c1 live convolution all day. It seems to require some very alien intuition to predict the output of two live signals convolved!

As expected, rhythmic impulses make very nice faux multitap delays. Incredible fun. I had a surprise when putting these triggers into a HP filter and modulating cutoff. I was just trying to shorten them up, but there must be a great sensitivity to impulse shape… If only I had a “Dirac function generator” to compare! It was Three Sisters HP so perhaps the unavoidable resonance was the culprit? Or perhaps I need to rectify the HP output to remove the falling edge’s negative impulse.

Making a “more traditional” IR on-the-fly is possible by pinging filters, Rings, etc, with shaped white noise impulses. But don’t expect it to sound too much like normal convo. reverb in the live mode.

R*S Resonant Equalizer, once again, is my star of the show when feedback patching c1 :star2:

Reaper’s “ReaVerb” has some nice tools for synthesizing, importing, manipulating and capturing IRs. it’s free with the DAW.

SOS has a good guide

https://www.soundonsound.com/techniques/reaverb-part-1
https://www.soundonsound.com/techniques/reaverb-part-2

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In the past, I’ve used single-sample piano and marimba sounds as impulse responses. They make for pretty interesting resonators.

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Using sounds that aren’t shaped like claps as IRs is a fascinating way to explore convolution. I’ve used room tones and sustained musical sounds as IRs and when you put white noise in to the convolver you get endless variations off those IRs. There are continuous variations and modulations of the IR sound when you put random noise as the input to the convolver. Putting a more coherent signal, like a rhythmic drum or a melody into the same IR creates more of a filtered effect.

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That makes sense when you remember that convolution accentuates frequencies that are common to both the source & the IR…

Many years ago I bought some IR collections from a company called Spiritcanyonaudio - their site is gone, but listening to the raw IRs is useful… Same for the SYBER IRs, some of theirs are like noisy decaying synth tones…
http://www.syberdelix.com/syverb/

@oot Thanks for making this thread. I can’t say I can I can contribute much to the discussion (yet), but I certainly like your impulse responses. Can you talk a bit how you made them? Did you end up using them anywhere?

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I’m not sure about the first one but the other two I’m using in a song each. I tend to create an IR with a specific project in mind and then archive it separately.

I tend to work with white noise, my sample collections of sounds I’ve recorded myself and whichever type of synthesis I can use that can produce sounds which do not reinforce too much of a specific frequency. So far it’s been pretty trial and error. I feel like I haven’t fully developed a technique for it but here’s what I remember of my thought process for creating the IR’s I can recall using:

The second one was made for vocals, I wanted to create an effect similar to Phil Collin’s reverse reverb vocal effect on In The Air Tonight, but still slightly weirder and more modern. The exponential attack of the noise creates the reverse effect and that click makes for a delay with a specific EQ profile. They’re then panned to widen the sound.

The third one is used as this huge ambient reverb swell that fades in at the end of the song it’s used in. The sweeping pitch of the sample I used creates a sweeping resonance effect in the reverb tail where each frequency comes in at a different time. The samples going on in stereo were used to create more definition and width to the sound.

@zoundsabar’s post made me think about the core of what convolution does to sound and I got inspired to do use a sine sweep as an IR. I think it’s a pretty cool sound that sort of exposes what is happening to the sound when you convolve.
This is the IR, as mention a sweeping sinewave:

Here is the dry sound, a pedal steel guitar:

Here it is going through the sine sweep, completely wet:

You can tell that each transient gets replaced with what sounds like a resonant filter sweep, while the notes with a softer attack seem to have slightly less resonance.

If you look at this sound in a spectrogram, you will see each overtone of the guitar be shifted in time to the same point in time that frequency occurs in the IR (it looks a bit like as if you tilted the sound, actually).

Each frequency only occurs once in this case so it doesn’t build up much resonance but if you were to prolong any frequency it would be like adding the same overlapping sound a few milliseconds after the original. A way I sometimes think of convolution is giving each millisecond snippet of each frequency the envelope of the corresponding frequency of the IR, or perhaps adding that envelope on on top of the existing dynamics of it.

My technical understanding of it is limited though, I can only really explain how I experience working with it.

I’m really curious now about creating drum sounds with convolution though. Sending noise bursts, pops, scratches into a drum hit as an IR is an interesting proposition, perhaps combined with frequency shifting for further dynamics. I’ll try to experiment with this and report back!

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This is a really interesting experiment, which reveals interesting properties of convolution, and it sounds cool too! The properties are that each sample of the input is put through a series of filters for the length of the IR. This happens for each input sample, and all the results are added together in the output, like you were saying here in other words.

A way I sometimes think of convolution is giving each millisecond snippet of each frequency the envelope of the corresponding frequency of the IR, or perhaps adding that envelope on on top of the existing dynamics of it.

I like the prospects of your new experiment and am looking forward to the results!

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A thing that sometimes sounds nice is using convolution in reverse - applying a tonal sample as an impulse response to some sort of a noise. Here I’m using a note of a Guitaret loaded into the convolution reverb to process some tape noise:

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How did you get it to produce several notes? This is the limitation I’ve found when I’ve tried this technique, I’ve always ended up wanting to add more than one note to the phrase.

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this might seem pedantic, but i think it’s interesting: convolution is commutative, so there is no actual difference between (A\circledast B) and (B \circledast A).

(of course in practice with audio, they are different because we are actually doing partitioned convolution; A and B are regions of different-length signals…)

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I’ve made percussion loops and loaded them as IRs, convolving short, tuned pulses, to create something a little like using drums as the modulator for a vocoder. And obviously you can’t change pitch midway through the pattern of the IR. But you can do some interesting things by e.g. playing with the shape of the input, or triggering inputs more often than the length of the IR. Longer envelopes will create slurring effects, more short input notes just layers the rhythms. Playing very high or low will have noticeable effects as well.

I’ll admit I never figured anything out using drums that sounds good enough to finish a piece. But in general I do like working with long, quite rhythmic IR’s and sparse input sounds. One of my contributions to this long track is the sort of chiming sound that shows up in the second half - skip past about 16 minutes to hear it mostly on its own - which is an example of this. From memory it’s short synth notes through a recording of hitting a pipe, which has an initial clang and then a couple more unevenly spaced. I tweaked the speed of the IR to suit the tempo.

PS. I first got into convolution from this guy Mugwood, who is Antony Ryan / one half of Isan. He uses shortwave off station as an IR and it makes for some nice effects. Sometimes you get sweeping sounds a bit like @oot 's beautiful sine wave sweeps.

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Still, when loading the tone as an inpulse, you can also modify it using the reverb controls (length, decay). And you can actually draw an envelope to the noise using automation, which changes the way that the tone impulse reacts :slight_smile:

I sampled the results for each note and made an instrument out of it :slight_smile:

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So, trying to parse this as a layman, convolution itself is the process of each pair of samples filtering each other (so to speak), with the implementation of a convolution reverb plugin would be that each sample of the live input gets convolved 100 times if the impulse response is 100 samples long?

(I’m probably using “sample” here wrong, I’m using it to mean slice of the frequency spectrum, had trouble finding what the actual term should be.)

Side point, this sounds lovely. I always think of these types of guitars as being a bit honky-tonk… but playing with the attack and sustain in this way really opens it up. Did you play this or is it a sample?

Back on topic, I have a mungo c0 and although I don’t fathom to know much about IR (or have ever made my own) I have loved being surprised by the way that a piece of source material can be so diversely affected.

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