LTspice - BigMuff sim

[Chris-S]

Hi,
I'm trying to simulate this schematic:

http://www.bigmuffpage.com/images/Kits_ ... ematic.jpg

in LTspice. I'm not sure if I modelled the input correctly. I added one DV power (9V) and one AC power for the input signal, is this the right way?



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Download latest version of Wuff - Distortion for REAPER
(other DAWs can load via http://reaper.fm/reaplugs ).

Version: 1.1 (14-Feb-2016)
http://chris-s.bplaced.net/div/wuff-for-reaper.zip

[resynthesis]

Been a while since I last used Spice but, from memory, it seems OK. Maybe the AC voltage is a bit big? If there are no more authoritative answers I'll try to find some of my old LTspice sims

[Chris-S]

I think this looks good (input = 0.1V, 200 hz sinus).

[Chris-S]

Ok, so I will use the following model for the plug:

Input stage:
hp and lp filter, variable gain (max 17 dB, "sustain").

clipping stage1:
23 dB gain, soft clip, lp filter

clipping stage2:
25 dB gain, soft clip, lp filter

tone control:
blend between hp and lp filter

For the soft clip I'use a kubic spline waveshaper modelled after the LTspice simulation for a diode clipper.

[alexirae]

Found this very descriptive too:
http://www.electrosmash.com/big-muff-pi-analysis

[Chris-S]

Thanks, already found that page.

Alpha version of the plugin (it's a JS plug for Reaper) is done.

[Chris-S]

Hi,
first version is ready for download.

It's called wuff.



Download link moved to first post.

[Yeager]

Hi Chris, it sounds lovely.

But when I load it in REAPER it gives a (loud) click,
also when I hit play it always gives a click (thunk) kind of sound.

Test is easy: open REAPER create new project, add wuff as an FX you hear a Thunk.
Then just press play and you hear a Thunk/Thud.

Or is it me ?

[Chris-S]

Hi,
I will check. Never noticed loud clicks while testing (Reaper V5.111).

Maybe it's caused by the DC offset which is intruduced by the asym clipper.

it sounds lovely.

Thanks.

[Chris-S]

I'm not sure if it's worth the effort to include some HQ (oversampling option).

It's clear that the distortion introduces some aliasing, but is the human ear able to notice those aliased harmonics between all the non-aliased harmonics?

Chris

[Ivan_C]

At least, I think it would be a good idea to add a DC remover at the end of the processing

[kvaca]

... is the human ear able to notice those aliased harmonics between all the non-aliased harmonics?
Chris

in normal scenario /when no pitchbending is involved/ human ear can not detect small aliasing directly...but when you start to play any pitchbending even small aliasing becames clearly hearable as a strange mirroring tone which is not present in analogue world

[Chris-S]

At least, I think it would be a good idea to add a DC remover at the end of the processing

There are already highpass filters build in.

[Ivan_C]

Sorry, now I have seen the code and tried the simulation, it sounds good !

For the clicks, that means that the initial values of the state variables might not be right at startup. I sent zeros (null signal) inside the plug-in, and I saw that z3 tends to be equal to 0.82702295 in this context.

Indeed, if you add the instruction "z3 = 0.82702295;" for the start values, after the z1 = z2 = z4 = 0 thing, the clicks diseappear.

[Chris-S]

Funny, 2 minutes ago I found the same fix:

@init

z1=z2=z4=z5=z6=z7=0;
z3=0.827;

So, with z3=0 the highpass filter needs some milliseconds to settle.

it sounds good

thanks.

I'm working on a HQ mode to make it even better.