Bifurcator documentation

doc/4-instrument/bifurcator.md

@@ -0,0 +1,38 @@
+# Bifurcator instrument editor
+
+Bifurcator instrument editor consists of these macros:
+
+- **Volume**: volume sequence.
+- **Arpeggio**: pitch sequence.
+- **Parametet**: set parameter of logistic map function.
+- **Panning (left)**: output level for left channel.
+- **Panning (right)**: output level for right channel.
+- **Pitch**: fine pitch.
+- **Load Value**: changes the current output value.
+
+## audio generation description
+
+Bifurcator uses logistic map iterations for sound generation.
+basically it runs the following function over and over:
+
+```
+r = (1 + (p / 65536)) * 2
+x = (r * x) * (1 - x)
+```
+
+where `x` is the current output value and `p` is the "parameter".
+
+by varying the parameter, the value of x may change drastically, producing a variety of sounds.
+the higher the parameter, the more "chaos" is present, effectively yielding noise.
+
+the default parameter is `47360`, which results in a square wave.
+
+if the parameter is set to 0, there's no sound at all.
+as the parameter approaches 32768, a decaying square wave is produced.
+the square wave stops decaying past 32768 and becomes louder until the parameter hits ~47496 (`r = 1 + sqrt(6)`).
+a second square wave one octave lower then starts appearing, until the parameter reaches ~51443 (`r ≈ 3.56995`). this is where chaos begins.
+anything higher results in a total mess.
+
+## the importance of loading the value
+
+you must load a value that isn't 0 in order to get sound. otherwise the function will always output 0.

doc/7-systems/bifurcator.md

@@ -1,3 +1,14 @@
 # Bifurcator
 
+this is a fantasy sound chip which uses a unique sound generation method: logistic map iterations.
 
+## effects
+
+- `10xx`: **set low byte of channel sample state.**
+- `11xx`: **set high byte of channel sample state.**
+- `12xx`: **set parameter low byte.**
+- `13xx`: **set parameter high byte.**
+
+## info
+
+this chip uses the [Bifurcator](../4-instrument/bifurcator.md) instrument editor.