13
0
livetrax/share/scripts/_amp4.lua
Robin Gareus 8edc94edea
Update a-Amplifier, use Ardour::Amp
This fixes an issue with a-Amp interpolating the parameter in dB,
resulting in a double-exponential fade when the parameter changes.

Now fade is linear in dB, also using Ardour' Amp processor is more
efficient, since interpolation happens in C++.
2020-04-19 00:49:43 +02:00

80 lines
2.3 KiB
Lua

ardour {
["type"] = "dsp",
name = "Simple Amp IV",
category = "Amplifier",
license = "MIT",
author = "Ardour Team",
description = [[Versatile +/- 20dB multichannel amplifier]]
}
function dsp_ioconfig ()
return
{
-- -1, -1 = any number of channels as long as input and output count matches
{ audio_in = -1, audio_out = -1},
}
end
function dsp_params ()
return
{
{ ["type"] = "input", name = "Gain", min = -20, max = 20, default = 0, unit="dB"},
}
end
local lpf = 0.02 -- parameter low-pass filter time-constant
local cur_gain = 0 -- current smoothed gain (dB)
-- called once when plugin is instantiated
function dsp_init (rate)
lpf = 780 / rate -- interpolation time constant
end
function low_pass_filter_param (old, new, limit)
if math.abs (old - new) < limit then
return new
else
return old + lpf * (new - old)
end
end
-- the DSP callback function
-- "ins" and "outs" are http://manual.ardour.org/lua-scripting/class_reference/#C:FloatArray
function dsp_run (ins, outs, n_samples)
local ctrl = CtrlPorts:array() -- get control port array (read/write)
local siz = n_samples -- samples remaining to process
local off = 0 -- already processed samples
local changed = false
-- if the gain parameter was changed, process at most 32 samples at a time
-- and interpolate gain until the current settings match the target values
if cur_gain ~= ctrl[1] then
changed = true
siz = 32
end
while n_samples > 0 do
if siz > n_samples then siz = n_samples end -- process at most "remaining samples"
if changed then
-- smooth gain changes above 0.02 dB difference
-- XXX this interpolates dB, resulting in a double-exponential fade XXX
cur_gain = low_pass_filter_param (cur_gain, ctrl[1], 0.02)
end
local gain = ARDOUR.DSP.dB_to_coefficient (cur_gain) -- 10 ^ (0.05 * cur_gain)
for c = 1,#ins do -- process all channels
-- check if output and input buffers for this channel are identical
-- http://manual.ardour.org/lua-scripting/class_reference/#C:FloatArray
if ins[c] ~= outs[c] then
-- http://manual.ardour.org/lua-scripting/class_reference/#ARDOUR:DSP
ARDOUR.DSP.copy_vector (outs[c]:offset (off), ins[c]:offset (off), siz)
end
ARDOUR.DSP.apply_gain_to_buffer (outs[c]:offset (off), siz, gain); -- apply-gain, process in-place
end
n_samples = n_samples - siz
off = off + siz
end
end