Java MIDI audio is delayed after laptop comes out of hibernation

Question

I'm developing a music programming language , and using the JVM (via Clojure) to play musical scores written in this language. So far, we are just using the javax.sound.midi MidiSynthesizer to play the scores.

Because Clojure has a slow startup time and we want to be able to play a score from the command-line and hear it immediately, we've chosen to structure the score interpreter as a background server process, and communicate with it using a more lightweight command-line client written in Java.

All of this is working great for the most part, however, there is a strange issue that we're seeing where if you start the server, then close your laptop* and let it hibernate, then open it again and have the server play a score, the audio doesn't happen immediately but is delayed for several seconds. Running the server with debug logging, I can actually see that the MIDI note on/off events are happening immediately (and timed correctly), but the audio is delayed.

*This may or may not be platform-specific. I'm seeing the issue on my 2014 Macbook Pro running OS X 10.9.5 Mavericks.

To help narrow it down, I put together this simple example (using Java, not Clojure) that demonstrates the problem:

https://github.com/daveyarwood/java-midi-delayed-audio-example

I've been scratching my head over this for a while now. Why is the audio delayed, and is there anything we can do about it?

Answer 1

This looks like a bug in Sun's implementation of Synthesizer.

I did not investigate this deeply, but I've found that the problem is apparently in Jitter Corrector that wraps AudioInputStream . Jitter Corrector thread relies on System.nanoTime() . However nanoTime may jump when a computer wakes up from standby or hibernate mode.

The work-around is to disable Jitter Corrector. You can do so by opening Synthesizer this way:

    synth = MidiSystem.getSynthesizer();

    if (synth instanceof com.sun.media.sound.SoftSynthesizer) {
        Map<String, Object> params = Collections.singletonMap("jitter correction", false);
        ((com.sun.media.sound.SoftSynthesizer) synth).open(null, params);
    } else {
       synth.open();
    }

Answer 2

In addition to @apangin's solution, I have found two other workarounds:

• Before each playback, close and re-open the same Synthesizer instance.

• Use a new Synthesizer instance for each playback.

Neither of these are ideal because it takes a couple seconds to open a synthesizer instance (even if it's an existing one that was previously open), but these workarounds may be sufficient for some use cases.