Add a DSP script to slowly fade in/out

diff --git a/scripts/a_slow_mute.lua b/scripts/a_slow_mute.lua
new file mode 100644 (file)
index 0000000..a9ef12b
--- /dev/null
+++ b/scripts/a_slow_mute.lua
@@ -0,0 +1,66 @@
+ardour {
+       ["type"]    = "dsp",
+       name        = "a-Slow-Mute",
+       category    = "Amplifier",
+       license     = "MIT",
+       author      = "Ardour Team",
+       description = [[Mute button with slow fade in/out]]
+}
+
+function dsp_ioconfig ()
+       -- -1, -1 = any number of channels as long as input and output count matches
+       return { { audio_in = -1, audio_out = -1} }
+end
+
+
+function dsp_params ()
+       return { { ["type"] = "input", name = "Mute", min = 0, max = 1, default = 0, toggled = true } }
+end
+
+local cur_gain = 1
+local lpf = 0.002 -- parameter low-pass filter time-constant
+
+function dsp_init (rate)
+       lpf = 100 / rate -- interpolation time constant
+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
+
+-- the DSP callback function
+-- "ins" and "outs" are http://manual.ardour.org/lua-scripting/class_reference/#C:FloatArray
+function dsp_run (ins, outs, n_samples)
+       local ctrl = CtrlPorts:array() -- get control port array
+       local target_gain = ctrl[1] > 0 and 0.0 or 1.0;  -- when muted, target_gain = 0.0; otherwise use 1.0
+       local siz = n_samples -- samples remaining to process
+       local off = 0 -- already processed samples
+       local changed = false
+
+       -- if the target gain changes, process at most 32 samples at a time,
+       -- and interpolate gain until the current settings match the target values
+       if cur_gain ~= target_gain then
+               changed = true
+               siz = 32
+       end
+
+       while n_samples > 0 do
+               if siz > n_samples then siz = n_samples end
+               if changed then
+                       cur_gain = low_pass_filter_param (cur_gain, target_gain, 0.001)
+               end
+
+               for c = 1,#ins do -- process all channels
+                       if ins[c] ~= outs[c] then
+                               ARDOUR.DSP.copy_vector (outs[c]:offset (off), ins[c]:offset (off), siz)
+                       end
+                       ARDOUR.DSP.apply_gain_to_buffer (outs[c]:offset (off), siz, cur_gain);
+               end
+               n_samples = n_samples - siz
+               off = off + siz
+       end
+end