ac_form is a patch for Max/MSP & Jitter which I use with an acoustic guitar. This patch makes it possible for the performer to add to what he plays live and in real time by resampling and synthesis on a computer.

At concerts I often had the problem that when I wanted to change the settings on the computer I had to take my hands off my guitar. So I decided to develop a system which would not just accompany what I was playing but produce a kind of interaction between the performer and the software.

To do this both the audio and video streams are analyzed, processed and then played again by the patch—though crossovers also occur: the video input influences not only the video output but also the audio output, and vice-versa. The patch requires absolutely no samples from other sources, all the sounds are generated by resampling and synthesis.

The patch is organized roughly in three sampler units that are functionally similar, as well as two synthesizer parts, a video subpatch and a main mixer with compatible analysis and randomization patches. The video subpatch analyzes an input signal, transforming it into an audio signal while also processing the video further, which in turn influences the audio stream.

The two step sequencers on the user interface trigger the synthesizer parts by playing userprogrammed presets that have been randomly selected during the performance by analyzing the audio stream. ac_form operates as stand-alone application based on the runtime version of Max/MSP.