feat: getSemitoneShift function

SoundGen/Synth.fs

@@ -7,31 +7,22 @@ open SoundGen.Oscillator
 let private getHzBySemitones semi =
     pitchStandard * (2. ** (1. / 12.)) ** semi
 
-let private getSemitonesByNote (str: string) =
-    let defaultOctave = 4
+let private getSemitoneShift (rootNote : string) (targetNote : string) : int =
+    // Define arrays to map pitch classes to numeric values and vice versa
+    let pitchClasses = [| "C"; "C#"; "D"; "D#"; "E"; "F"; "F#"; "G"; "G#"; "A"; "A#"; "B" |]
+    let pitchClassValues = [| 0; 1; 2; 3; 4; 5; 6; 7; 8; 9; 10; 11 |]
     
-    let notes =
-        [ "A"
-          "A#"
-          "B"
-          "C"
-          "C#"
-          "D"
-          "D#"
-          "E"
-          "F"
-          "F#"
-          "G"
-          "G#" ]
-        |> List.toArray
+    // Extract the note number and pitch class for the root note
+    let rootNoteNum = int (rootNote.Substring(rootNote.Length - 1))
+    let rootPitchClass = Array.findIndex ((=) (rootNote.Substring(0, rootNote.Length - 1))) pitchClasses
     
-    let octave =
-        str.Substring(str.Length - 1) |> int
+    // Extract the note number and pitch class for the target note
+    let targetNoteNum = int (targetNote.Substring(targetNote.Length - 1))
+    let targetPitchClass = Array.findIndex ((=) (targetNote.Substring(0, targetNote.Length - 1))) pitchClasses
     
-    let noteShift =
-        Array.findIndex (fun e -> e = str.Substring(0, str.Length - 1)) notes
+    // Calculate the semitone shift using the formula
+    (targetNoteNum - rootNoteNum) * 12 + (targetPitchClass - rootPitchClass)
 
-    (octave - defaultOctave - 1) * 12 + noteShift
 
 
 let private freq hz duration (osc: OscillatorParameter list) =
@@ -75,6 +66,6 @@ let note semitone beats =
     freq
         hz
         (beats * beatDuration)
-        [ { Osc = Sine; Freq = hz / 4. };
-           { Osc = Saw; Freq = (hz + 1.) };
-           { Osc = Saw; Freq = (hz - 1.3) } ]
+        [ { Osc = Saw; Freq = hz / 4. };
+           { Osc = Saw; Freq = hz+0.5 };
+           { Osc = Saw; Freq = hz-1. } ]