Synthesizing distorted guitar from MIDI

Question

So I've been experimenting with generating music by computer program, and got a thing working with Python and fluidsynth, with a nice-sounding piano soundfont. I want to switch to distorted electric guitar sound, though. The problem is that a chord on a distorted guitar is made like this:

string vibration → multiple strings mixed by pickups → distortion

whereas anything based on soundfonts would be more like this:

string vibration → distortion → multiple samples mixed by synth

Distortion needs to happen after the strings are mixed together in order to sound correct.

What are my options? I could get a soundfont of undistorted guitar and then take the output of the synth and run it through a separate distortion program? In Linux this could be done with JACK, but I've been using Windows and is there an equivalent functionality there? Or maybe there's MIDI synths that support distortion?

Answer 1

There's of course plenty of ways to do that. The easiest way on Windows would certainly be to load both a SoundFont synth and an amp-simulator plugin into a DAW, but I suppose that's not the solution you want.

If you'd like to keep it down to a single executable and, as I suspect, you're more interested seeing in how intonation influences distortion-intermodulation than achieving an actual guitar sound, I'd suggest hacking a distortion patch into fluidsynth. If you're not fussy about aliasing (well I know you are...) then a basic distortion is laughably simple to implement, just do something like

U ↦ tanh(U + ^U2/₂ + ^U3/₃)

on the samples, to get both tube-bias like even overtones and smooth saturation. This will of course not sound like a proper overdriven guitar amp, but it's actually not that bad either – if you convolute the result with an impulse-response from a guitar cabinet (or, as an approximation thereof, apply a primitive third-order IIR lowpass at 7000 Hz and some random band boosts) then such a simple nonlinearity can sound surprisingly convincing.

Answer 2

Unfortunately it is tough to generate a good sounding distorted guitar using only digital means. Although as sampling gets better this is slowly getting better as well.

Your idea of sampling a clean guitar sound and then routing it though a distortion unit and back into your DAW would be the route I would take assuming you cant get your hands on a real guitar and guitar player.

The basic issue you have is more or less as follows,

Distortion is in a nutshell a sound that occurs when your signal is out side of the range your amplifier or pre-amp can handle. This causes a "distorted" sound. Most of the time you are trying to avoid this in audio as you generally want a clean signal. However guitar happens to sound really nice when distorted and such distortion as an effect, and not a negative byproduct of using equipment incorrectly was born. Now the issue with the digital world is that when you have the same problem (a signal top great for the input) you end up with clipping. This is just in the form of unpleasant noise generally. Thus it is hard to recreate distortion by simply overdriving inputs (the way it was done in the analog world). This is why most distortion emulators dont sound as good as the real thing. No matter your sample source any artificially distorted sample will always sound like one. My advice is to find a local guitarist (they are all over the place) and record him playing the riff you desire.