I've recently had problems with sound using Core Audio - I get glitches with frame sizes around 128 samples. Smaller frame sizes work better, and larger also ( but not always ). The problem doesn't always happen, but will always turn up if you switch the frame sizes around a few times.
I can reproduce the problem in all version of JUCE from 3.0.0 up tp 3.0.4. If I put the 2.1.8 version of juce_audio_basics and juce_audio_devices into a new JUCE version then the problem goes away.
What seems to be happening is that empty frames are being inserted into the input and the ouput stream at (apparently) random intervals. I have checked the methods in juce_MacCoreAudio.cpp and traced the problem back to the data read/write in the run() method of the combiner class. I haven't yet worked out exactly how this works, so I'm currently no help with debugging. When I have some time I'll try and trace it further. Unfortunately I just upgraded my last Mac to Mavericks, so I can't test an earlier OS version
The problem also happens in the JUCE demo. To be sure I built a program with the absolute minimum that I need to play a sound and change framesize - no problem with 2.1.8 and glitches with 3.0.0 upwards. Just for the record, and I've attached the program.
Here's my basic info:
Computer: MacBook pro 15" (mid 2013) with 16Gb memory and 500Gb disk
OS : OSX Mavericks 10.9.2
Audio : Intel HIgh Definition Audio