Convolution and Impulse Response

Alex Harker will be leading one of nine community-driven workshops at Expo ’74 in Brooklyn this October. Read on for more information about his workshop and some history of his work.




Convolution and Impulse Response Workshop (using HISSTools)

The workshop will present a new set of tools for working with convolution and impulse responses in MaxMSP (HISSTools impulse response toolbox). Rather than than being simply an exposition of these new externals, the aim of the workshop will be to provide participants with some theoretical background to impulse response measurement, as well as tools and practical skills to work with convolution for a range of applications (reverb, creative effects, measurement, speaker and room correction etc.).

The exact nature of the workshop would depend on the available resources, but areas to be covered include:

  • Impulse response measurement of real spaces / electronic systems
  • Speaker / room correction from IR measurements
  • Mic correction
  • Realtime and non-realtime convolution
  • Deconvolution and inversion of impulse responses
  • Non-linear convolution

Participants will have a chance to investigate the objects and techniques in small groups or individually, depending on the equipment available.

Participants will require a reasonably fast computer running MaxMSP. Soundcards / mics / hardware to measure etc. also useful but non-essential.

A Short Interview with Alex Harker

Who are you and what do you do?

I’m a composer and programmer based in the UK. I write music for various combinations of instruments and electronics, both fixed and live (see some recent work). As a programmer, I spend a lot of time developing externals for MaxMSP. Most of my external development has arisen out of creative projects that I couldn’t realise in Max alone, but it has become a pretty serious occupation in itself. I recently released a set of 82 externals written during my PhD study at the University of York.

Currently I’m working as a Research Fellow at the University of Huddersfield, creating a set of tools primarily for MaxMSP called HISSTools. This workshop is based around the first set of objects from this work which are focussed on impulse response measurement and manipulation.

When and why did you start using Max?

I started using Max in 2004 as part of University course I was attending during my Masters programme at the University of Birmingham. I have a fairly extensive background in music technology and I already had an interest in how audio processing worked, so using Max was a totally logical step. It probably took off a lot faster than I would have guessed, and I got into coding externals within a few months. That was partly because I was really interested in spectral processing, and it is a lot easier to do some of that stuff in C than with native objects only.

What technology or person’s work intrigues you most right now?

I’m getting back into the idea of sines + noise + transient modelling and returning to spectral processing (partly due to doing a fair amount of it for HISSTools). I did a whole lot of reading up on this model a couple of years back, and then it didn’t really fit into the project I was working on. It was also hard at the time for me to figure out how to implement that kind of approach entirely within Max. Now I have a slightly different take on it though, as I’m interested in abstracting a “model” of a sound that can be used quite malleably, rather than getting a realistic reproduction of the original. I’m hoping to achieve what I want without the need for too much complexity.

Perhaps ironically, given that I’m presenting on convolution which for a lot of people is mostly about reverb, I’m also really into algorithmic reverb at the moment. I’m using Aether by 2caudio, which I’ve been really really impressed by in terms of flexibility and sheer sound quality. I’m very interested at the moment in finding really high-quality DSP tools and I’d love to know more about how to make an algorithmic reverb of this kind of quality. However, I’m aware that this is the kind of area that can become a black hole in terms of time, so for the time being I’m leaving it to the experts…

What is the most exciting part of attending Expo ’74?

Like everyone else, I’m most excited to meet people in the community, see their work and discuss ideas. It’s nice to have an excuse to visit New York for the first time also!

Learn More About Alex

Convolution and Impulse Response

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