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livetrax/scripts/HiAndLowPass.lua

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ardour {
["type"] = "dsp",
name = "a-High/Low Pass Filter",
category = "Filter",
license = "GPLv2",
author = "Ardour Team",
description = [[High and Low Pass Filter with de-zipped controls, written in Ardour-Lua]]
}
function dsp_ioconfig ()
return
{
-- allow any number of I/O as long as port-count matches
{ audio_in = -1, audio_out = -1},
}
end
function dsp_params ()
return
{
{ ["type"] = "input", name = "High Pass Steepness", min = 0, max = 4, default = 1, enum = true, scalepoints =
{
["Off"] = 0,
["12dB/oct"] = 1,
["24dB/oct"] = 2,
["36dB/oct"] = 3,
["48dB/oct"] = 4,
}
},
{ ["type"] = "input", name = "High Pass Cut off frequency", min = 5, max = 20000, default = 100, unit="Hz", logarithmic = true },
{ ["type"] = "input", name = "High Pass Resonance", min = 0.1, max = 6, default = .707, logarithmic = true },
{ ["type"] = "input", name = "Low Pass Steepness", min = 0, max = 4, default = 1, enum = true, scalepoints =
{
["Off"] = 0,
["12dB/oct"] = 1,
["24dB/oct"] = 2,
["36dB/oct"] = 3,
["48dB/oct"] = 4,
}
},
{ ["type"] = "input", name = "Low Pass Cut off frequency", min = 20, max = 20000, default = 18000, unit="Hz", logarithmic = true },
{ ["type"] = "input", name = "Low Pass Resonance", min = 0.1, max = 6, default = .707, logarithmic = true },
}
end
-- these globals are *not* shared between DSP and UI
local hp = {} -- the biquad high-pass filter instances (DSP)
local lp = {} -- the biquad high-pass filter instances (DSP)
local filt = nil -- the biquad filter instance (GUI, response)
local cur = {0, 0, 0, 0, 0, 0} -- current parameters
local lpf = 0.03 -- parameter low-pass filter time-constant
local chn = 0 -- channel/filter count
local lpf_chunk = 0 -- chunk size for audio processing when interpolating parameters
local max_freq = 20000
local mem = nil -- memory x-fade buffer
function dsp_init (rate)
-- allocate some mix-buffer
mem = ARDOUR.DSP.DspShm (8192)
-- max allowed cut-off frequency
max_freq = .499 * rate
-- create a table of objects to share with the GUI
local tbl = {}
tbl['samplerate'] = rate
tbl['max_freq'] = max_freq
self:table ():set (tbl)
-- Parameter smoothing: we want to filter out parameter changes that are
-- faster than 15Hz, and interpolate between parameter values.
-- For performance reasons, we want to ensure that two consecutive values
-- of the interpolated "steepness" are less that 1 apart. By choosing the
-- interpolation chunk size to be 64 in most cases, but 32 if the rate is
-- strictly less than 22kHz (there's only 8kHz in standard rates), we can
-- ensure that steepness interpolation will never change the parameter by
-- more than ~0.86.
lpf_chunk = 64
if rate < 22000 then lpf_chunk = 32 end
-- We apply a discrete version of the standard RC low-pass, with a cutoff
-- frequency of 15Hz. For more information about the underlying math, see
-- https://en.wikipedia.org/wiki/Low-pass_filter#Discrete-time_realization
-- (here Δt is lpf_chunk / rate)
local R = 2 * math.pi * lpf_chunk * 15 -- Hz
lpf = R / (R + rate)
end
function dsp_configure (ins, outs)
assert (ins:n_audio () == outs:n_audio ())
local tbl = self:table ():get () -- get shared memory table
chn = ins:n_audio ()
cur = {0, 0, 0, 0, 0, 0}
hp = {}
lp = {}
collectgarbage ()
for c = 1, chn do
hp[c] = {}
lp[c] = {}
-- initialize filters
-- http://manual.ardour.org/lua-scripting/class_reference/#ARDOUR:DSP:Biquad
-- A different Biquad is needed for each pass and channel because they
-- remember the last two samples seen during the last call of Biquad:run().
-- For continuity these have to come from the previous audio chunk of the
-- same channel and pass and would be clobbered if the same Biquad was
-- called several times by cycle.
for k = 1,4 do
hp[c][k] = ARDOUR.DSP.Biquad (tbl['samplerate'])
lp[c][k] = ARDOUR.DSP.Biquad (tbl['samplerate'])
end
end
end
function santize_params (ctrl)
-- don't allow manual cross-fades. enforce enums
ctrl[1] = math.floor(ctrl[1] + .5)
ctrl[4] = math.floor(ctrl[4] + .5)
-- high pass, clamp range
ctrl[2] = math.min (max_freq, math.max (5, ctrl[2]))
ctrl[3] = math.min (6, math.max (0.1, ctrl[3]))
-- low pass, clamp range
ctrl[5] = math.min (max_freq, math.max (20, ctrl[5]))
ctrl[6] = math.min (6, math.max (0.1, ctrl[6]))
return ctrl
end
-- helper functions for parameter interpolation
function param_changed (ctrl)
for p = 1,6 do
if ctrl[p] ~= cur[p] then
return true
end
end
return false
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
-- apply parameters, re-compute filter coefficients if needed
function apply_params (ctrl)
if not param_changed (ctrl) then
return
end
-- low-pass filter ctrl parameter values, smooth transition
cur[1] = low_pass_filter_param (cur[1], ctrl[1], 0.05) -- HP order x-fade
cur[2] = low_pass_filter_param (cur[2], ctrl[2], 1.0) -- HP freq/Hz
cur[3] = low_pass_filter_param (cur[3], ctrl[3], 0.01) -- HP quality
cur[4] = low_pass_filter_param (cur[4], ctrl[4], 0.05) -- LP order x-fade
cur[5] = low_pass_filter_param (cur[5], ctrl[5], 1.0) -- LP freq/Hz
cur[6] = low_pass_filter_param (cur[6], ctrl[6], 0.01) -- LP quality
for c = 1, chn do
for k = 1,4 do
hp[c][k]:compute (ARDOUR.DSP.BiquadType.HighPass, cur[2], cur[3], 0)
lp[c][k]:compute (ARDOUR.DSP.BiquadType.LowPass, cur[5], cur[6], 0)
end
end
end
-- the actual DSP callback
function dsp_run (ins, outs, n_samples)
assert (n_samples <= 8192)
assert (#ins == chn)
local ctrl = santize_params (CtrlPorts:array ())
local changed = false
local siz = n_samples
local off = 0
-- if a parameter was changed, process at most lpf_chunk samples
-- at a time and interpolate parameters until the current settings
-- match the target values
if param_changed (ctrl) then
changed = true
siz = lpf_chunk
end
while n_samples > 0 do
if changed then apply_params (ctrl) end
if siz > n_samples then siz = n_samples end
local ho = math.floor(cur[1])
local lo = math.floor(cur[4])
-- process all channels
for c = 1, #ins do
-- High Pass
local xfade = cur[1] - ho
-- prepare scratch memory
ARDOUR.DSP.copy_vector (mem:to_float (off), ins[c]:offset (off), siz)
-- run at least |ho| biquads...
for k = 1,ho do
hp[c][k]:run (mem:to_float (off), siz)
end
ARDOUR.DSP.copy_vector (outs[c]:offset (off), mem:to_float (off), siz)
-- mix the output of |ho| biquads (with weight |1-xfade|)
-- with the output of |ho+1| biquads (with weight |xfade|)
if xfade > 0 then
ARDOUR.DSP.apply_gain_to_buffer (outs[c]:offset (off), siz, 1 - xfade)
hp[c][ho+1]:run (mem:to_float (off), siz)
ARDOUR.DSP.mix_buffers_with_gain (outs[c]:offset (off), mem:to_float (off), siz, xfade)
-- also run the next biquad because it needs to have the correct state
-- in case it start affecting the next chunck of output. Higher order
-- ones are guaranteed not to be needed for the next run because the
-- interpolated order won't increase more than 0.86 in one step thanks
-- to the choice of the value of |lpf|.
if ho + 2 <= 4 then hp[c][ho+2]:run (mem:to_float (off), siz) end
elseif ho + 1 <= 4 then
-- run the next biquad in case it is used next chunk
hp[c][ho+1]:run (mem:to_float (off), siz)
end
-- Low Pass
xfade = cur[4] - lo
-- prepare scratch memory (from high pass output)
ARDOUR.DSP.copy_vector (mem:to_float (off), outs[c]:offset (off), siz)
-- run at least |lo| biquads...
for k = 1,lo do
lp[c][k]:run (mem:to_float (off), siz)
end
ARDOUR.DSP.copy_vector (outs[c]:offset (off), mem:to_float (off), siz)
-- mix the output of |lo| biquads (with weight |1-xfade|)
-- with the output of |lo+1| biquads (with weight |xfade|)
if xfade > 0 then
ARDOUR.DSP.apply_gain_to_buffer (outs[c]:offset (off), siz, 1 - xfade)
lp[c][lo+1]:run (mem:to_float (off), siz)
ARDOUR.DSP.mix_buffers_with_gain (outs[c]:offset (off), mem:to_float (off), siz, xfade)
-- also run the next biquad in case it start affecting the next
-- chunck of output.
if lo + 2 <= 4 then lp[c][lo+2]:run (mem:to_float (off), siz) end
elseif lo + 1 <= 4 then
-- run the next biquad in case it is used next chunk
lp[c][lo+1]:run (mem:to_float (off), siz)
end
end
n_samples = n_samples - siz
off = off + siz
end
if changed then
-- notify display
self:queue_draw ()
end
end
-------------------------------------------------------------------------------
--- inline display
function round (n)
return math.floor (n + .5)
end
function freq_at_x (x, w)
-- frequency in Hz at given x-axis pixel
return 20 * 1000 ^ (x / w)
end
function x_at_freq (f, w)
-- x-axis pixel for given frequency, power-scale
return w * math.log (f / 20.0) / math.log (1000.0)
end
function db_to_y (db, h)
-- y-axis gain mapping
if db < -60 then db = -60 end
if db > 12 then db = 12 end
return -.5 + round (0.2 * h) - h * db / 60
end
function grid_db (ctx, w, h, db)
-- draw horizontal grid line
-- note that a cairo pixel at Y spans [Y - 0.5 to Y + 0.5]
local y = -.5 + round (db_to_y (db, h))
ctx:move_to (0, y)
ctx:line_to (w, y)
ctx:stroke ()
end
function grid_freq (ctx, w, h, f)
-- draw vertical grid line
local x = -.5 + round (x_at_freq (f, w))
ctx:move_to (x, 0)
ctx:line_to (x, h)
ctx:stroke ()
end
function response (ho, lo, f)
-- calculate transfer function response for given
-- hi/po pass order at given frequency [Hz]
local db = ho * filt['hp']:dB_at_freq (f)
return db + lo * filt['lp']:dB_at_freq (f)
end
function render_inline (ctx, w, max_h)
if not filt then
local tbl = self:table ():get () -- get shared memory table
-- instantiate filter (to calculate the transfer function's response)
filt = {}
filt['hp'] = ARDOUR.DSP.Biquad (tbl['samplerate'])
filt['lp'] = ARDOUR.DSP.Biquad (tbl['samplerate'])
max_freq = tbl['max_freq']
end
local ctrl = santize_params (CtrlPorts:array ())
-- set filter coefficients if they have changed
if param_changed (ctrl) then
for k = 1,6 do cur[k] = ctrl[k] end
filt['hp']:compute (ARDOUR.DSP.BiquadType.HighPass, cur[2], cur[3], 0)
filt['lp']:compute (ARDOUR.DSP.BiquadType.LowPass, cur[5], cur[6], 0)
end
-- calc height of inline display
local h = 1 | math.ceil (w * 9 / 16) -- use 16:9 aspect, odd number of y pixels
if (h > max_h) then h = max_h end -- but at most max-height
-- ctx is a http://cairographics.org/ context
-- http://manual.ardour.org/lua-scripting/class_reference/#Cairo:Context
-- clear background
ctx:rectangle (0, 0, w, h)
ctx:set_source_rgba (.2, .2, .2, 1.0)
ctx:fill ()
ctx:rectangle (0, 0, w, h)
ctx:clip ()
-- set line width: 1px
ctx:set_line_width (1.0)
-- draw grid
local dash3 = C.DoubleVector ()
local dash2 = C.DoubleVector ()
dash2:add ({1, 2})
dash3:add ({1, 3})
ctx:set_dash (dash2, 2) -- dotted line: 1 pixel 2 space
ctx:set_source_rgba (.5, .5, .5, .8)
grid_db (ctx, w, h, 0)
ctx:set_dash (dash3, 2) -- dashed line: 1 pixel 3 space
ctx:set_source_rgba (.5, .5, .5, .5)
grid_db (ctx, w, h, -12)
grid_db (ctx, w, h, -24)
grid_db (ctx, w, h, -36)
grid_freq (ctx, w, h, 100)
grid_freq (ctx, w, h, 1000)
grid_freq (ctx, w, h, 10000)
ctx:unset_dash ()
-- draw transfer function line
local ho = math.floor(cur[1])
local lo = math.floor(cur[4])
ctx:set_source_rgba (.8, .8, .8, 1.0)
ctx:move_to (-.5, db_to_y (response(ho, lo, freq_at_x (0, w)), h))
for x = 1,w do
local db = response(ho, lo, freq_at_x (x, w))
ctx:line_to (-.5 + x, db_to_y (db, h))
end
-- stoke a line, keep the path
ctx:stroke_preserve ()
-- fill area to zero under the curve
ctx:line_to (w, -.5 + round (db_to_y (0, h)))
ctx:line_to (0, -.5 + round (db_to_y (0, h)))
ctx:close_path ()
ctx:set_source_rgba (.5, .5, .5, .5)
ctx:fill ()
return {w, h}
end
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