Hardware insert confusion - help!

[justinhill]

I'm very confused.

Preparing to test some outboard I've just bought, I have patched my Quantum 4848 interface with outputs 7-8 connected to inputs 7-8.

Opening a session I happen to be working on right now I can instantiate an insert on the master bus (i/o 7-8) and everything works as it should (it's a 96k session and 408 samples of extra delay appear).

But if I instantiate the i/o insert on any audio track or any aux track fed by one or more audio tracks (stereo, i/o 7-8; mono, i/o 7 or 8) I get hideous spitting/crackling noise superimposed on the audio. This is true even if I put the insert onto a track that doesn't happen to have any clips on it, and true if I insert it on one track and solo a different track.

The only place I can put this insert without this happening apart from the master bus is on a stereo aux with a reverb on it being fed from 'sends'.

I'm doing something wrong here but I can't get my head round it.

[justinhill]

I've figured it out by myself - or at least found out what was going on.

The trouble-maker is Ozone 8. If I de-active it, everything works as it should. Put any other plug-in in its place and everything still works as it should.

I can make it work with Ozone 8 if I put the playback buffer size to its maximum setting (2048), even though the session doesn't require that setting without hardware inserts. And even though Pro Tools should have stopped with an error message, not carried on playing with distortion, if that was the problem. By the way, I have "Ignore errors during playback..." UNchecked.