From abdcfb5ec271fe585e93f7d79bd109996d5294b2 Mon Sep 17 00:00:00 2001
From: Robin Haberkorn <robin.haberkorn@googlemail.com>
Date: Mon, 30 May 2016 00:23:16 +0200
Subject: implemented delay lines and echo effect

 * DelayStream must currently have a constant length (ie. duration)
 * Stream:mix() allows mixing two streams by a constant wet/dryness factor.
   0 means only the first stream, while 1 is only the second stream.
 * Stream:echo() builds on this for an echo effect with constant delay
   and wetness factor. The source stream is automatically synced.
---
 applause.lua | 51 +++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 51 insertions(+)

diff --git a/applause.lua b/applause.lua
index 06e3242..91c879a 100644
--- a/applause.lua
+++ b/applause.lua
@@ -327,6 +327,20 @@ function Stream:ravel()
 	return RavelStream:new(self)
 end
 
+function Stream:mix(other, wetness)
+	wetness = wetness or 0.5
+	return self:mul(1 - wetness) + other:mul(wetness)
+end
+
+function Stream:delay(length)
+	return DelayStream:new(self, length)
+end
+
+function Stream:echo(length, wetness)
+	local synced = self:sync()
+	return synced:mix(synced:delay(length), wetness)
+end
+
 -- This is a linear resampler thanks to the
 -- semantics of IndexStream
 function Stream:resample(factor)
@@ -1509,6 +1523,43 @@ function PinkNoiseStream:tick()
 	end
 end
 
+--
+-- Delay Lines
+-- NOTE: Echoing could be implemented here as well since
+-- delay lines are only an application of echoing with a wetness of 1.0.
+-- However this complicates matters because we have to handle nil.
+--
+
+DelayStream = DeriveClass(MuxableStream)
+
+DelayStream.sig_last_stream = 1
+
+function DelayStream:muxableCtor(stream, length)
+	self.streams = {stream}
+	self.length = length
+	if length < 1 then error("Invalid delay line length") end
+end
+
+function DelayStream:tick()
+	local tick = self.streams[1]:tick()
+	local length = self.length
+	local buffer = table.new(length, 0)
+	local buffer_pos = 1
+
+	for i = 1, length do buffer[i] = 0 end
+
+	return function()
+		local sample = buffer[buffer_pos]
+		buffer[buffer_pos] = tick()
+		buffer_pos = (buffer_pos % length) + 1
+		return sample
+	end
+end
+
+function DelayStream:len()
+	return self.length + self.streams[1]:len()
+end
+
 --
 -- MIDI Support
 --
-- 
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