demo your computer's builtin synthesizer sounds using middle C

midi-synth-demo.clj

(import 'javax.sound.midi.Synthesizer 'javax.sound.midi.MidiSystem)

; plays a middle C for 2 seconds, then pauses for 500ms
(defn play [channel]
    (do
        (.noteOn channel 67 1)
        (Thread/sleep 2000)
        (.allNotesOff channel)
        (Thread/sleep 500)))

; why doesn't with-open work here?
(def synth (doto (MidiSystem/getSynthesizer) .open))

(for [x (range (count (.getChannels ^Synthesizer synth)))] 
    (let [channel (aget (.getChannels ^Synthesizer synth) x)] 
        (play channel)))