Julien _FrnchFrgg_ RIVAUD
d527fdf30a
And beef up comments for readers using the filter as an example.
358 lines
10 KiB
Lua
358 lines
10 KiB
Lua
ardour {
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["type"] = "dsp",
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name = "a-High/Low Pass Filter",
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category = "Filter",
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license = "GPLv2",
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author = "Ardour Team",
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description = [[An Ardour High and Low Pass Filter with de-zipped controls, written in Lua]]
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}
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function dsp_ioconfig ()
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return
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{
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-- allow any number of I/O as long as port-count matches
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{ audio_in = -1, audio_out = -1},
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}
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end
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function dsp_params ()
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return
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{
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{ ["type"] = "input", name = "High Pass Steepness", min = 0, max = 4, default = 1, enum = true, scalepoints =
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{
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["Off"] = 0,
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["12dB/oct"] = 1,
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["24dB/oct"] = 2,
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["36dB/oct"] = 3,
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["48dB/oct"] = 4,
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}
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},
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{ ["type"] = "input", name = "High Pass Cut off frequency", min = 5, max = 20000, default = 100, unit="Hz", logarithmic = true },
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{ ["type"] = "input", name = "High Pass Resonance", min = 0.1, max = 6, default = .707, logarithmic = true },
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{ ["type"] = "input", name = "Low Pass Steepness", min = 0, max = 4, default = 1, enum = true, scalepoints =
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{
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["Off"] = 0,
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["12dB/oct"] = 1,
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["24dB/oct"] = 2,
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["36dB/oct"] = 3,
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["48dB/oct"] = 4,
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}
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},
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{ ["type"] = "input", name = "Low Pass Cut off frequency", min = 20, max = 20000, default = 18000, unit="Hz", logarithmic = true },
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{ ["type"] = "input", name = "Low Pass Resonance", min = 0.1, max = 6, default = .707, logarithmic = true },
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}
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end
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-- these globals are *not* shared between DSP and UI
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local hp = {} -- the biquad high-pass filter instances (DSP)
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local lp = {} -- the biquad high-pass filter instances (DSP)
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local filt = nil -- the biquad filter instance (GUI, response)
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local cur = {0, 0, 0, 0, 0, 0} -- current parameters
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local lpf = 0.03 -- parameter low-pass filter time-constant
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local chn = 0 -- channel/filter count
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local mem = nil -- memory x-fade buffer
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function dsp_init (rate)
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-- allocate some mix-buffer
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mem = ARDOUR.DSP.DspShm (8192)
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-- create a table of objects to share with the GUI
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local tbl = {}
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tbl['samplerate'] = rate
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self:table ():set (tbl)
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-- interpolation time constant, ~15Hz @ 64fpp
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lpf = 5000 / rate
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end
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function dsp_configure (ins, outs)
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assert (ins:n_audio () == outs:n_audio ())
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local tbl = self:table ():get () -- get shared memory table
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chn = ins:n_audio ()
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cur = {0, 0, 0, 0, 0, 0}
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hp = {}
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lp = {}
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collectgarbage ()
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for c = 1, chn do
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hp[c] = {}
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lp[c] = {}
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-- initialize filters
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-- http://manual.ardour.org/lua-scripting/class_reference/#ARDOUR:DSP:Biquad
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-- A different Biquad is needed for each pass and channel because they
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-- remember the last two samples seen during the last call of Biquad:run().
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-- For continuity these have to come from the previous audio chunk of the
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-- same channel and pass and would be clobbered if the same Biquad was
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-- called several times by cycle.
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for k = 1,4 do
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hp[c][k] = ARDOUR.DSP.Biquad (tbl['samplerate'])
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lp[c][k] = ARDOUR.DSP.Biquad (tbl['samplerate'])
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end
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end
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end
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-- helper functions for parameter interpolation
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function param_changed (ctrl)
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for p = 1,6 do
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if ctrl[p] ~= cur[p] then
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return true
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end
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end
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return false
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end
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function low_pass_filter_param (old, new, limit)
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if math.abs (old - new) < limit then
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return new
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else
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return old + lpf * (new - old)
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end
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end
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-- apply parameters, re-compute filter coefficients if needed
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function apply_params (ctrl)
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if not param_changed (ctrl) then
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return
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end
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-- low-pass filter ctrl parameter values, smooth transition
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cur[1] = low_pass_filter_param (cur[1], ctrl[1], 0.05) -- HP order x-fade
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cur[2] = low_pass_filter_param (cur[2], ctrl[2], 1.0) -- HP freq/Hz
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cur[3] = low_pass_filter_param (cur[3], ctrl[3], 0.01) -- HP quality
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cur[4] = low_pass_filter_param (cur[4], ctrl[4], 0.05) -- LP order x-fade
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cur[5] = low_pass_filter_param (cur[5], ctrl[5], 1.0) -- LP freq/Hz
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cur[6] = low_pass_filter_param (cur[6], ctrl[6], 0.01) -- LP quality
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for c = 1, chn do
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for k = 1,4 do
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hp[c][k]:compute (ARDOUR.DSP.BiquadType.HighPass, cur[2], cur[3], 0)
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lp[c][k]:compute (ARDOUR.DSP.BiquadType.LowPass, cur[5], cur[6], 0)
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end
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end
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end
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-- the actual DSP callback
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function dsp_run (ins, outs, n_samples)
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assert (n_samples < 8192)
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assert (#ins == chn)
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local changed = false
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local siz = n_samples
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local off = 0
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-- if a parameter was changed, process at most 64 samples at a time
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-- and interpolate parameters until the current settings match
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-- the target values
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if param_changed (CtrlPorts:array ()) then
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changed = true
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siz = 64
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end
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while n_samples > 0 do
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if changed then apply_params (CtrlPorts:array ()) end
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if siz > n_samples then siz = n_samples end
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local ho = math.floor(cur[1])
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local lo = math.floor(cur[4])
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-- process all channels
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for c = 1, #ins do
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-- High Pass
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local xfade = cur[1] - ho
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-- prepare scratch memory
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ARDOUR.DSP.copy_vector (mem:to_float (off), ins[c]:offset (off), siz)
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-- run at least |ho| biquads...
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for k = 1,ho do
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hp[c][k]:run (mem:to_float (off), siz)
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end
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ARDOUR.DSP.copy_vector (outs[c]:offset (off), mem:to_float (off), siz)
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-- mix the output of |ho| biquads (with weight |1-xfade|)
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-- with the output of |ho+1| biquads (with weight |xfade|)
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if xfade > 0 then
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ARDOUR.DSP.apply_gain_to_buffer (outs[c]:offset (off), siz, 1 - xfade)
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hp[c][ho+1]:run (mem:to_float (off), siz)
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ARDOUR.DSP.mix_buffers_with_gain (outs[c]:offset (off), mem:to_float (off), siz, 1 - xfade)
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ho = ho + 1 -- to avoid running another time the biguad |ho+1|
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end
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-- run remaining biquads because they need to have the correct state
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-- in case they start affecting the next chunck of output
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-- TODO: only run the ones that have a chance to run next cycle
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for k = ho+1,4 do
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hp[c][k]:run (mem:to_float (off), siz)
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end
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-- Low Pass
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xfade = cur[4] - lo
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-- prepare scratch memory (from high pass output)
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ARDOUR.DSP.copy_vector (mem:to_float (off), outs[c]:offset (off), siz)
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-- run at least |lo| biquads...
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for k = 1,lo do
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lp[c][k]:run (mem:to_float (off), siz)
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end
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ARDOUR.DSP.copy_vector (outs[c]:offset (off), mem:to_float (off), siz)
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-- mix the output of |lo| biquads (with weight |1-xfade|)
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-- with the output of |lo+1| biquads (with weight |xfade|)
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if xfade > 0 then
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ARDOUR.DSP.apply_gain_to_buffer (outs[c]:offset (off), siz, 1 - xfade)
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lp[c][lo+1]:run (mem:to_float (off), siz)
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ARDOUR.DSP.mix_buffers_with_gain (outs[c]:offset (off), mem:to_float (off), siz, 1 - xfade)
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lo = lo + 1 -- to avoid running another time the biguad |lo+1|
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end
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-- again, run remaining biquads
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for k = lo+1,4 do
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lp[c][k]:run (mem:to_float (off), siz)
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end
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end
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n_samples = n_samples - siz
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off = off + siz
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end
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if changed then
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-- notify display
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self:queue_draw ()
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end
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end
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-------------------------------------------------------------------------------
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--- inline display
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function round (n)
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return math.floor (n + .5)
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end
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function freq_at_x (x, w)
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-- frequency in Hz at given x-axis pixel
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return 20 * 1000 ^ (x / w)
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end
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function x_at_freq (f, w)
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-- x-axis pixel for given frequency, power-scale
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return w * math.log (f / 20.0) / math.log (1000.0)
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end
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function db_to_y (db, h)
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-- y-axis gain mapping
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if db < -60 then db = -60 end
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if db > 12 then db = 12 end
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return -.5 + round (0.2 * h) - h * db / 60
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end
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function grid_db (ctx, w, h, db)
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-- draw horizontal grid line
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-- note that a cairo pixel at Y spans [Y - 0.5 to Y + 0.5]
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local y = -.5 + round (db_to_y (db, h))
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ctx:move_to (0, y)
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ctx:line_to (w, y)
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ctx:stroke ()
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end
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function grid_freq (ctx, w, h, f)
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-- draw vertical grid line
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local x = -.5 + round (x_at_freq (f, w))
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ctx:move_to (x, 0)
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ctx:line_to (x, h)
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ctx:stroke ()
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end
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function response (ho, lo, f)
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-- calculate transfer function response for given
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-- hi/po pass order at given frequency [Hz]
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local db = ho * filt['hp']:dB_at_freq (f)
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return db + lo * filt['lp']:dB_at_freq (f)
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end
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function render_inline (ctx, w, max_h)
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if not filt then
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local tbl = self:table ():get () -- get shared memory table
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-- instantiate filter (to calculate the transfer function's response)
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filt = {}
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filt['hp'] = ARDOUR.DSP.Biquad (tbl['samplerate'])
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filt['lp'] = ARDOUR.DSP.Biquad (tbl['samplerate'])
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end
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-- set filter coefficients if they have changed
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if param_changed (CtrlPorts:array ()) then
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local ctrl = CtrlPorts:array ()
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for k = 1,6 do cur[k] = ctrl[k] end
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filt['hp']:compute (ARDOUR.DSP.BiquadType.HighPass, cur[2], cur[3], 0)
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filt['lp']:compute (ARDOUR.DSP.BiquadType.LowPass, cur[5], cur[6], 0)
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end
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-- calc height of inline display
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local h = 1 | math.ceil (w * 9 / 16) -- use 16:9 aspect, odd number of y pixels
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if (h > max_h) then h = max_h end -- but at most max-height
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-- ctx is a http://cairographics.org/ context
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-- http://manual.ardour.org/lua-scripting/class_reference/#Cairo:Context
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-- clear background
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ctx:rectangle (0, 0, w, h)
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ctx:set_source_rgba (.2, .2, .2, 1.0)
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ctx:fill ()
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ctx:rectangle (0, 0, w, h)
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ctx:clip ()
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-- set line width: 1px
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ctx:set_line_width (1.0)
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-- draw grid
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local dash3 = C.DoubleVector ()
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local dash2 = C.DoubleVector ()
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dash2:add ({1, 2})
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dash3:add ({1, 3})
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ctx:set_dash (dash2, 2) -- dotted line: 1 pixel 2 space
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ctx:set_source_rgba (.5, .5, .5, .8)
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grid_db (ctx, w, h, 0)
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ctx:set_dash (dash3, 2) -- dashed line: 1 pixel 3 space
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ctx:set_source_rgba (.5, .5, .5, .5)
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grid_db (ctx, w, h, -12)
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grid_db (ctx, w, h, -24)
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grid_db (ctx, w, h, -36)
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grid_freq (ctx, w, h, 100)
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grid_freq (ctx, w, h, 1000)
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grid_freq (ctx, w, h, 10000)
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ctx:unset_dash ()
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-- draw transfer function line
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local ho = math.floor(cur[1])
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local lo = math.floor(cur[4])
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ctx:set_source_rgba (.8, .8, .8, 1.0)
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ctx:move_to (-.5, db_to_y (response(ho, lo, freq_at_x (0, w)), h))
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for x = 1,w do
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local db = response(ho, lo, freq_at_x (x, w))
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ctx:line_to (-.5 + x, db_to_y (db, h))
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end
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-- stoke a line, keep the path
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ctx:stroke_preserve ()
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-- fill area to zero under the curve
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ctx:line_to (w, -.5 + round (db_to_y (0, h)))
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ctx:line_to (0, -.5 + round (db_to_y (0, h)))
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ctx:close_path ()
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ctx:set_source_rgba (.5, .5, .5, .5)
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ctx:fill ()
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return {w, h}
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end
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