My shot at creating a 16x oversampled guitar processor. It's an attempt at a "minimalist" patch. Here's a link to the Pd patch, although the demo uses an LV2 plugin (see below video demo link):

https://github.com/GModal/AUCOP/tree/master/AUCOP-guitarToy16x/pd

I doubt the oversampling is done in a "textbook" way, but it sounds OK. I'd enjoy any discussion or input about oversampling -- or anything else in the patch...

The parent Dir has the Pd patch, plus Camomile LV2 and VST plugins (for linux currently). But it should be trivial to make iOS or Windows versions of the plugins. I didn't do that, 'cause I can't test the plugins. The Camomile "Example" files are included.

https://github.com/GModal/AUCOP

@gmoon What is oversampling in a textbook way?

@ricky I guess (as I understand it...or not), the upsampled signal should be zero-padded, and followed by a "textbook" FIR filter (sorry for the "textbook" again!) or alternately, another low pass filter with similar characteristics.

I initially couldn't find any info re: Pd's upsampling algorithm. And I was fairly constrained to vanilla (by Camomile). I did eventually find the default upsampling when reblocking is not to pad (sample/hold). But the patch was written, and seemed to work ok.

Re: low pass after upsampling -- I used a vcf~ filter, followed by a regular lop~, hoping that might hit the cpu less.

Sorry again about the textbook thing. Fact is, I don't have one.

Might be helpful if I post the patch, rather than require folks to clone the whole repository and wade in to get to the Pd code:

AUCOP-guitarToy16x.zip

Loaded the original in Purr Data on my Debian install, and the patch didn't sound correct. It was clear the default upsampling in Purr is zero-padded, unlike stock vanilla Pd. I knew the upsample schema was an issue with the original (aliasing-wise).

This is good; a chance to examine the patch with a fresh perspective.

The changes required weren't radical -- first needed to recover some amplitude that's lost with zero padding (where that's done mattered). Added a Pre-Level control. The differences do change the waveform, so tweaked most of the presets as well. I think it's an improvement, particularly for the higher-gain presets.

Zero-padding is explicit now, so that's for vanilla too. This might effect (positively) other flavors as well.

Sorry, no demo currently, just the updated patch. And nothing changed on github -- no Camomile plugin versions yet. Upcoming...

Edit:
guitar_toy16X_V0.63_release.zip deleted.

One corrupt line in the 0.63 preset file ("red clay") caused errors. Here's V0.64:
guitar_toy16X_V0.64_release.zip

@gmoon Interesting. Not sure on the conventions regarding zero padding - I thought switch~ took care of all that for you in Pd, no? It is conventional to have either an IIR or FIR depending on your needs in terms of latency and phase distortion. Not something I've really pursued in Pd either. lop~ should definitely hit the CPU less than vcf~, correct. vcf~, if memory serves, is better suited if you want access to real and imaginary parts but could be consider band and low-pass outputs respectively.

@ricky It's actually set in the [inlet~] obj, and the padding documentation is buried four clicks deep in the help file (under "pd up/downsampling"). It took me some time to find that.

If (my) memory serves, one lop~ stage didn't have a sufficient cutoff, and I liked having the option (and sound) of setting the resonance in vcf~. At this point I've replaced that two-stage scheme with a single biquad~ filter. It seems to be a bit quieter with the higher gain patches (and might even hit the cpu less).

Anyway, there's a new version (with somewhat different version style #, 0.1.71) of the Pd patch:
AUCOP-guitarToy16X_pd0.1.71.zip

I'd planned on making a short demo vid before updating this thread, but no time like the present...

The github page has the Camomile LV2 and VST3 plugins for this version (still Linux only -- but the Camomile code is there, so it should be easy to build plugins for Win & Mac).

Cool. I like the sound of this project. I'd love to see a video!

@ricky Thx! I'm trying to get it together...

OK, here's a newer video of the plugin:

Arrg. Just found a typo (should be "encapsulate" not "encapulates".)

Again, should have included the non-plugin Pd version for evaluation:

guitar_toy16X_V0.71a_release.zip

There's a folder in the archive (.AUCOP) that holds extra presets. On a Linux system it should be in the user's home path (I've never tested that on other systems). It's not absolutely necessary, and the "Load Presets" file dialog should just open in the default Pd dir, if it's not found.

Edit: Oops, I kinda already did that above. This is different only in changes to the extra preset file...

A couple incremental updates to this project (Pd code not functionally changed, so the above non-plugin version OK):

• The sample rate wasn't being correctly recognized in the plugins, due to differences in Pd and Camomile conventions (see the pic to compare). The Pd version always worked correctly, but the Camomile plugin didn't set the lowpass filter values correctly. Tested at 96000 and 192000 sps.

(Pd code left, Camomile right)

This makes some sense -- for a plugin, when does loadbang actually happen?

• Fixed some annoying xruns on an older machine's Debian install of the plugins, which occurred following a preset file load. Probably resulted from weird values being passed to JACK ports, due to the "rolling" parameter order updating. Fix is to mute the output during update.

Still @:
https://github.com/GModal/AUCOP/tree/master/AUCOP-guitarToy16x

Thx!!
D

Possible future updates (???): make oversample rate changeable...having adjustable aliasing w/greater harmonic distortion can be good...

Fix the lowpass filter values to reflect actual frequencies.