在Javasound中播放多个样本

Question

I'm looking to write a simple MIDI-driven audio sequencer using Javasound.

I have multiple samples (one for each MIDI pitch) that are loaded into memory as a (globally accessible) Map<MidiPitch,AudioInputStream> .

A custom subclass of javax.sound.midi.Receiver responds to incoming MIDI events as follows:

If the event is a note-on, a Clip is obtained and played as follows:

Clip clip = AudioSystem.getClip();
clip.open(lookupAIS(pitch));
clip.start();

The clip is then added to a globally accessible Map<MidiPitch,List<Clip>> , representing started clips , ie clips for which start() has been called as above, but for which a note-off event has not yet been received.

If the event is a note-off, the corresponding list of started clips is obtained from the above map. The clip at the head of the list is removed, and stop() and close() are called on it.

The above Receiver is connected to MidiSystem.getSequencer() in the usual way, then the following called:

sequencer.setSequence(MidiSystem.getSequence(new File(myMidFile)))
sequencer.open()
sequencer.start()

Thread.sleep(aLongTime())

sequencer.stop()
sequencer.close()

The above works when the driving MIDI sequence is at a slow tempo, but at higher tempos, notes simply hang (even for sequences containing a very small number of notes).

My understanding is that clip.start() is run within a separate thread behind the scenes by the Javasound API.

Can anyone suggest why this might be happening? Is it perhaps a synchronization issue?

EDIT: By 'hang', I mean that some notes are stuck, despite the fact that log output reports that the corresponding 'stop' method has been called.

EDIT2: It looks as if the hanging first happens when a given note is played for the second time. This happens even if the MIDI sequence is monophonic, ie the previous note has stopped.

Answer 1

Your method of loading the Clip for each play is going to be a considerable source of variable latency. Every time you call this, the file is read anew and will not start playing until it the entire file has finished loading.

I recommend pre-loading all the clips and holding them in memory. When the note-on is called, set the clip cursor to zero and then play:

clip[mapIndex].setFramePosition(0);
clip[mapIndex].start();

These clips should have already been opened. I'm putting them in an array and using "mapIndex" as a plausible way of selecting the correct clip that might work with the mapping you've already set up.

You probably won't need to "stop" or "close" the clips until the entire sequence has finished, unless the clips are rather long and are designed to be stopped while in progress, or if they are being played as loops.

This should improve things considerably. I can't say if it will fix everything. The cpu is probably doing some thread multiplexing, and it is plausible that occasionally, in your current code, the clip.close is being called on one thread before the clip has finished loading on the other.