Fix a typo in HiAndLowPass.lua

Instead of mixing two consecutive biquad orders with a linear xfade, the
code used the same weight for both signals to mix, due to a copy-paste
blunder. Brown-bag fix this now. Also change a little the threshold for
using 32-samples chunks to cater for steepness jumping from 0 to 4 (this
doesn't change anything for commonly used rates and is just for
robustness in never-happening cases anyway).

diff --git a/scripts/HiAndLowPass.lua b/scripts/HiAndLowPass.lua
index 3694ec315b38247520dbb93de1e592a101c02880..1c1b0686e5246a09efd92a55da69c5878bfdb824 100644 (file)
--- a/scripts/HiAndLowPass.lua
+++ b/scripts/HiAndLowPass.lua
@@ -70,11 +70,11 @@ function dsp_init (rate)
        -- 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 16kHz (there's only 8kHz in standard rates), we can
+       -- 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 ~0.82.
+       -- more than ~0.86.
        lpf_chunk = 64
-       if rate < 16000 then lpf_chunk = 32 end
+       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
@@ -198,11 +198,11 @@ function dsp_run (ins, outs, n_samples)
                        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, 1 - xfade)
+                               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 0.8 in one step thanks
+                               -- 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
@@ -227,7 +227,7 @@ function dsp_run (ins, outs, n_samples)
                        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, 1 - xfade)
+                               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