Optimize a-HiAndLowPass
- Better formula for the lpf smoothness parameter. It is computed only on init and rate change anyway... - Only run as many Biquads as needed to save computing power, esp. when using low steepness and parameters are not changing.
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@ -4,7 +4,7 @@ ardour {
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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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description = [[High and Low Pass Filter with de-zipped controls, written in Ardour-Lua]]
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}
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function dsp_ioconfig ()
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@ -52,6 +52,7 @@ 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 lpf_chunk = 0 -- chunk size for audio processing when interpolating parameters
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local mem = nil -- memory x-fade buffer
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@ -64,8 +65,22 @@ function dsp_init (rate)
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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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-- Parameter smoothing: we want to filter out parameter changes that are
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-- faster than 15Hz, and interpolate between parameter values.
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-- For performance reasons, we want to ensure that two consecutive values
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-- of the interpolated "steepness" are less that 1 apart. By choosing the
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-- interpolation chunk size to be 64 in most cases, but 32 if the rate is
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-- strictly less than 16kHz (there's only 8kHz in standard rates), we can
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-- ensure that steepness interpolation will never change the parameter by
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-- more than ~0.82.
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lpf_chunk = 64
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if rate < 16000 then lpf_chunk = 32 end
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-- We apply a discrete version of the standard RC low-pass, with a cutoff
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-- frequency of 15Hz. For more information about the underlying math, see
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-- https://en.wikipedia.org/wiki/Low-pass_filter#Discrete-time_realization
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-- (here Δt is lpf_chunk / rate)
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local R = 2 * math.pi * lpf_chunk * 15 -- Hz
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lpf = R / (R + rate)
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end
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function dsp_configure (ins, outs)
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@ -148,12 +163,12 @@ function dsp_run (ins, outs, n_samples)
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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 a parameter was changed, process at most lpf_chunk samples
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-- at a time and interpolate parameters until the current settings
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-- match 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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siz = lpf_chunk
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end
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while n_samples > 0 do
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@ -184,14 +199,15 @@ function dsp_run (ins, outs, n_samples)
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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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-- also run the next biquad because it needs to have the correct state
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-- in case it start affecting the next chunck of output. Higher order
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-- ones are guaranteed not to be needed for the next run because the
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-- interpolated order won't increase more than 0.8 in one step thanks
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-- to the choice of the value of |lpf|.
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if ho + 2 <= 4 then hp[c][ho+2]:run (mem:to_float (off), siz) end
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elseif ho + 1 <= 4 then
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-- run the next biquad in case it is used next chunk
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hp[c][ho+1]:run (mem:to_float (off), siz)
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end
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-- Low Pass
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@ -212,12 +228,12 @@ function dsp_run (ins, outs, n_samples)
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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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-- also run the next biquad in case it start affecting the next
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-- chunck of output.
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if lo + 2 <= 4 then lp[c][lo+2]:run (mem:to_float (off), siz) end
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elseif lo + 1 <= 4 then
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-- run the next biquad in case it is used next chunk
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lp[c][lo+1]:run (mem:to_float (off), siz)
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end
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end
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