Apple Event: May 7th at 7 am PT
When setting up an Aggregate Device with my Mac's Built-In audio and an external Thunderbolt interface (Zoom Tac-2), which device should be the master and which should be the slave? In other words, which device should have "drift correction" enabled, the Built-In or the external device?
The clock on the interface should be the master.
Generally speaking....
The one that is not your main recording device (built-in?) should have drift correction enabled.
What's happening is there are two digital clocks, the TB Zoom and the Built-in, they will not be the same, one may be 44.10356 another may be 44.10128 over time they will drift apart, the device with drift correction software resamples one audio stream to match the other. It's always been a bit of a crapshoot with Aggregate devices.
oops.. sorry DSS, glad we both said the same thing.
When you setup the aggregate device - in the top of the window there is an option for the clock source. You pick the one you want to be the master. This one will not have drift correction applied to it, but all others used in the aggregate setup should have drift correction enabled.
This is actually handled automatically when you select the clock source. What you should see if (for example) 3 devices in your aggregate setup and you pick device #2 to be the master clock. Device #2 will disable the drift correction, while Devices #1, #3 will have their drift correction check boxes checked.
So you don't have to worry about this setting - Just select which device is going to be the master. ( it doesn't matter which ). OS X handles checking the correct pitch drift boxes for you.
Rule: Master clock should not have drift correction enabled - all others should.
Thank you everyone for the helpful answers! I had the Zoom TAC-2 setup as the "clock source" with drift correction enabled on the built-in outup.
Related question: what is the audible effect of drift correction vs no drift correct? The same signal sent to two different outputs get's pitched up down, or things get flammy without drift correction?
Once in a while I get a very strange effect of hearing things suddenly slow way down, like a record player that was turned off, then suddenly pick back up.. I don't know if this is related to using an Aggregate Device, or drift correction, or is just something strange going on with my software or the Zoom TAC-2.
Usually if the clocks aren't matched digitally you will hear a slight ticking sound in the quiet spots... depends on how far off the clocks are as to how slow or fast the ticking occurs, or even a slight/quiet static in the background as your audio files are slowly being shredded apart. (kidding....mostly)
That's with hardware clock sync, not sure about software drift correction, the sound you describe could be related to an Aggregate device losing sync but more Likely with the Zoom TAC-2 driver. (if it has one?)
Drift correction with Aggregate Devices?
