soundgen/SoundGen/Synth.fs

module SoundGen.Synth

open Settings
open Oscillator

let private getHzBySemitones semi =
    pitchStandard * (2. ** (1. / 12.)) ** semi

let private getSemitoneShiftInternal (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" |]

    // 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

    // 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

    // Calculate the semitone shift using the formula
    (targetNoteNum - rootNoteNum) * 12 + (targetPitchClass - rootPitchClass)

let private freq hz duration (osc: OscillatorParameter list) =
    let samples = seq { 0.0 .. (duration * sampleRate) }

    let attack =
        let samplesToRise = (sampleRate * (0.001 * attackMs))

        let risingDelta = 1. / samplesToRise
        let mutable i = 0.

        seq {
            while true do
                i <- i + risingDelta
                yield min i 1.
        }

    let output =
        Seq.map (fun x -> multiosc { Oscillators = osc; Sample = x } |> (*) volume) samples

    let adsrLength = Seq.length output

    let attackArray = attack |> Seq.take adsrLength

    let release = Seq.rev attackArray

    Seq.zip3 release attackArray output |> Seq.map (fun (x, y, z) -> (x * y * z))

let getSemitoneShift (targetNote: string) : int =
    getSemitoneShiftInternal "A4" targetNote

let note semitone beats =
    let hz = getHzBySemitones (semitone)

    freq
        hz
        (beats * beatDuration)
        [ { Osc = Saw; Freq = hz / 4. }
          { Osc = Saw; Freq = hz + 0.5 }
          { Osc = Saw; Freq = hz - 1. } ]