I’ve set up an AudioEngine with the below code.

It can play notes with the MIDISampler. However, the PitchTap doesn’t seem to get any sample data. It always prints Frequency 100.0 – Amplitude 2.4266092e-05.

final class AudioGraph {
    let engine = AudioEngine()
    let sampler = MIDISampler(name: "sampler")
    let pitchTracker: PitchTap

    init(file: SamplerFile? = nil) throws {
        let mic = engine.input!

        engine.output = Mixer(
            sampler, 
            Fader(mic, gain: 0.000)
        )

        /// Hooking ``PitchTap`` to ``sampler`` works. Yay. Why not the ``mic`` input?
        pitchTracker = PitchTap(mic) { f, a in
            guard let f = f.first, let a = a.first else { return }
            print("Frequency (f) – Amplitude (a)")
        }

        if let file {
            try setFile(file)
        }
    }

    func setFile(_ file: SamplerFile) throws {
        try sampler.loadInstrument(url: file.url)
    }
}

// MARK: -

extension AudioGraph: NotePlayer {
    func startAudioEngine() throws {
        print("### Start engine")
        try engine.start()
        pitchTracker.start()
    }
}