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]] } 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