clean interface

src/lib/utils/pitch.ts

@@ -0,0 +1,33 @@
+const NOTE_NAMES = ['C', 'C#', 'D', 'D#', 'E', 'F', 'F#', 'G', 'G#', 'A', 'A#', 'B'];
+const A4_FREQUENCY = 440;
+const A4_MIDI_NOTE = 69;
+
+export function noteToFrequency(noteName: string): number | null {
+  const match = noteName.match(/^([A-G]#?)(-?\d+)$/i);
+  if (!match) return null;
+
+  const [, note, octave] = match;
+  const noteIndex = NOTE_NAMES.indexOf(note.toUpperCase());
+  if (noteIndex === -1) return null;
+
+  const octaveNum = parseInt(octave, 10);
+  const midiNote = (octaveNum + 1) * 12 + noteIndex;
+  const semitonesDiff = midiNote - A4_MIDI_NOTE;
+
+  return A4_FREQUENCY * Math.pow(2, semitonesDiff / 12);
+}
+
+export function parseFrequencyInput(input: string): number | null {
+  const trimmed = input.trim();
+
+  const asNumber = parseFloat(trimmed);
+  if (!isNaN(asNumber) && asNumber > 0 && asNumber < 20000) {
+    return asNumber;
+  }
+
+  return noteToFrequency(trimmed);
+}
+
+export function formatFrequency(frequency: number): string {
+  return frequency.toFixed(2);
+}