Hi, I am currently trying to rebuild the stereo enhancer effect in lua. Now it turns out that the “surround” effect isn’t just a simple stereo rotator, it does more than that, but I don’t know what it is 
Any idea maybe? Thanks.
Maybe it LFO modulates the 90 degree signal with the inverted LFO on the -90 degree signal? Or 0° with 90°?
Curious how you would do this in lua? Are you looking at offline processing?
Anyway on a slight tangent, I found that the Stereo Enhancer is not mono compatible so I made a doofer out of native EQ’s which works fine in mono as well… It was in the downloads section in the old forum but I can’t find that here so I have attached it: Mono 2 Stereo 1.1.xrdp (36.6 KB)
@afta8 thank you! Though I am looking for a replacement vst for usage in Bitwig conversions, so I am using the LUA Protoplug VST and already created a very similar plugin now, maybe even more useful due using a variable allpass filter.
The stereo enhancer is useful for me esp. on material which originally wasn’t mono compatible, so the logic is like: not mono compatible + not mono compatible = mono compatible 
Still that surround algorithm… I really think now it leaks in the middle signal into the side and vice versa, done by purpose, in a modulated way. That’s why I once thought it was buggy and reported it as a bug, assuming it should have been a simple stereo rotation, but in fact, it isn’t that simple.
Maybe something like this:
http://www.musicdsp.org/en/latest/Effects/255-stereo-field-rotation-via-transformation-matrix.html
Ah yes, exactly this one I added, but it is a “usual” stereo rotator, but the surround algorithm has some additional “magic” going on.
im using the multiband FX with the tool loaded so i can play with the width …its that what you want to achieve or you like the character of the renoise effect ? 
sorry to interrupt - is that chain or native multiband fx device?
sorry, i overlooked that! i’m aware, i was excited to see something similar in renoise, so i had to jump in. 
Thanks again!
np bro
since it’s bitwig talk, i love the way processing works, how you can add pre to (for example) , post/pre fx for reverb, for distortion only wet fx, or so… it’s opening a lot of ways!
Hi, yes, it is a VST. Yes, I want to recreate the character of that device, for super accurate conversion 
Here is the code of the current version, currently lacking of “surround” and parameter interpolation, so do not automate it. Also this may be what a serious audio engineer would consider as harmful. But actually you could use it to make a synth phasing by purpose:
-- ffx Stereo Expander
--
-- missing: surround
-- with additional basic stereo rotator
require "include/protoplug"
local cbFilter = require "include/dsp/cookbook filters"
local width = 1
local phase = 0
local sur = 0
local apmix = 0
local monofreq = 0
local filter
local filterMono
local filterMono2
local swaplr = "off"
local lSample, rSample, panning, panning0
function stereoWiden(LSample, RSample, myWidth)
local mono = (LSample+RSample) * 0.5
local stereo = LSample - RSample
stereo = stereo * myWidth
return mono+stereo, mono-stereo
end
function phaseRotate(in_left, in_right)
local phasepi = phase * math.pi
out_left = (in_left * math.cos(phasepi)) - (in_right * math.sin(phasepi + math.pi));
out_right = (in_left * -math.sin(phasepi)) - (in_right * math.cos(phasepi + math.pi));
return out_left, out_right
end
function surround(in_left, in_right)
out_left = in_left;
out_right = out_right;
return out_left, out_right
end
stereoFx.init()
function stereoFx.Channel:init()
-- create per-channel fields (filters)
filter = cbFilter
{
-- initialize filters with current param values
type = "ap";
f = params[5].getValue()/2; -- 10 ... 20000
gain = 0; -- -30 ... 30
Q = params[6].getValue(); -- 0.1 ... 30
}
filterMono = cbFilter
{
-- initialize filters with current param values
type = "lp";
f = params[9].getValue()/2; -- 10 ... 20000
gain = 0; -- -30 ... 30
Q = 0.2; -- 0.1 ... 30
}
filterMono2 = cbFilter
{
-- initialize filters with current param values
type = "lp";
f = params[9].getValue()/2; -- 10 ... 20000
gain = 0; -- -30 ... 30
Q = 0.2; -- 0.1 ... 30
}
end
function plugin.processBlock(samples, smax)
for i = 0, smax do
samples[0][i], samples[1][i] =
samples[0][i] * (1-panning0),
samples[1][i] * (1+panning0)
;
samples[0][i], samples[1][i] = stereoWiden(samples[0][i], samples[1][i], width)
samples[0][i], samples[1][i] = phaseRotate(samples[0][i], samples[1][i])
samples[0][i], samples[1][i] = surround(samples[0][i], samples[1][i])
if (apmix >= 0) then
samples[0][i], samples[1][i] = samples[0][i], apmix * filter.process(samples[1][i]) + (1-apmix) * samples[1][i]
else
samples[0][i], samples[1][i] = apmix * filter.process(samples[0][i]) + (1-apmix) * samples[0][i], samples[1][i]
end
samples[0][i], samples[1][i] =
samples[0][i] * (1-panning),
samples[1][i] * (1+panning)
;
if (monofreq >= 20) then
lSample, rSample = filterMono.process(samples[0][i]), filterMono2.process(samples[1][i])
samples[0][i], samples[1][i] = lSample-samples[0][i], rSample-samples[1][i]
lSample, rSample = stereoWiden(lSample, rSample, 0)
samples[0][i], samples[1][i] =
samples[0][i]*0.5+lSample+samples[0][i]*0.5,
samples[1][i]*0.5+rSample+samples[1][i]*0.5
end
if (swaplr == "on") then
samples[0][i], samples[1][i] = samples[1][i], samples[0][i]
end
end
end
params = plugin.manageParams {
{
name = "Pre Pan";
min = -100;
max = 100;
default = 0;
changed = function(val) panning0=val/100 end;
},
{
name = "Width %";
min = 0;
max = 250;
default = 100;
changed = function(val) width=val/200 end;
},
{
name = "(Surround)";
min = 0;
max = 100;
default = 0;
changed = function(val) sr=val/100 end;
},
{
name = "Phase";
min = -90;
max = 90;
default = 0;
changed = function(val) phase=(-val)/180 end;
},
{
name = "AP freq";
min = 10;
max = 20000;
default = 440;
changed = function(val) filter.update{f=val} end;
},
{
name = "AP rez";
min = 0.1;
max = 5;
default = 0.1;
changed = function(val) filter.update{Q=val} end;
},
{
name = "AP mix";
min = -100;
max = 100;
default = 0;
changed = function(val) apmix=val/100 end;
},
{
name = "Pan";
min = -100;
max = 100;
default = 0;
changed = function(val) panning=val/100 end;
},
{
name = "Mono freq";
min = 0;
max = 20000;
default = 440;
changed = function(val) monofreq=val;filterMono.update{f=val};filterMono2.update{f=val} end;
},
{
name = "Swap L/R";
type = "list";
values = {"off"; "on"};
default = "off";
changed = function(val) swaplr = val end;
};
}
Paste it into lua protoplug. I guess you also could highpass the side, but this just is magic!
If you carefully setup it up and are using mono checks in between, then I think you can actually get quite good results with this.
This part seems to be extremely slow, I am not sure why, maybe using math lib is very slow?
function phaseRotate(in_left, in_right)
local phasepi = phase * math.pi
out_left = (in_left * math.cos(phasepi)) - (in_right * math.sin(phasepi + math.pi));
out_right = (in_left * -math.sin(phasepi)) - (in_right * math.cos(phasepi + math.pi));
return out_left, out_right
end
Only in one Renoise project, not in Bitwig…?¿?
maybe try to make local copies of sin/cos/pi in initialisation could make it work better?
Also could it maybe be optimised as “sin(phase+pi) = -sin(phase)” and “cos(phase+pi) = -cos(phase)”, saving a sin and a cos operation… Being save from sin is always a good operation.
Thanks for those optimizations, but I don’t think this is the problem, must be kind of denormals that happened. Now I even cannot reproduce it anymore… Weird.