
I've been looking into VSTs recently as a way to emulate analog stompboxes. I'm actually a bit disappointed by how few effect emulations there are,
especially with free VSTs. So, I pulled out an old copy of SynthEdit (from back when the free version allowed your VSTs to have backgrounds), and
I've made an emulation of the MXR Distortion+. It took a bit of research, especially for emulating the diode clippers. Most diode models are
iterative, which would be too time-consuming for a realtime effect. After some experimenting with functions, I ended up using Vout=arctan(6*Vin)/7 to
simulate the whole clipping setup.
Here's the structure of the whole effect:
Input attenuator -> Input HPF -> Pickup simulation LPF -> Op amp gain -> Op amp HPF -> Op amp bandwidth LPF -> Op amp clipper -> Output HPF -> Output LPF -> Output attenuator -> Diode clipping emulation -> Volume
And here's the file:
http://sites.google.com/site/distorque/home/vsts/distortion/Distorque-Dist%2B.zipThe controls:
These two are the original Distortion+ controls:
Output - Controls the output level.
Distortion - Controls the distortion and some of the filtering.
These are controls I've added to emulate other factors in the sound of a physical pedal:
Input Type - 'Pickup' adds a low-pass filter on the input to emulate the interaction between the 1nF cap on the input and a guitar pickup. 'Buffered' removes this filter.
Input level - This is a linear volume control on the input of the effect. At maximum, the pedal acts as if 0dB = 2VP. This goes all the way down to no input.
I don't own a Distortion+ but I've compared the VST to a LTSpice sim of a D+. Here are the results:
http://sites.google.com/site/distorque/home/vsts/distortion/Distortion%2Bcomparison.mp3And this is the file put through an amp sim (Voxengo Boogex)
https://sites.google.com/site/distorque/home/vsts/distortion/Distortion%2Bcomparisonamped.mp3The VST is first, the sim is second. Personally, I can't tell the difference, but maybe someone with better ears can tell me what differences they hear.
This VST isn't finished, but I'm looking for people to test this out and give feedback on it. I'm planning to improve, if necessary, the op amp clipping emulation, the diode clipping emulation, the 'Pickup' setting, the CPU usage, and the GUI, but I'd like other suggestions. Also, I'd like someone to compare this to a real MXR D+ and tell me how it sounds in comparison.
So, what do you guys think?