Audio MIDI Set Up

[musickid]

Ive joined this forum to try and find the answer to a question that i cant find elsewhere. i use an external digital to analogue convertor (dac) with my imac late 2013 27inch. the dac is linked to a dedicated headphone amplifier. i want to be 100% sure that the clock in the dac is the one being used and NOT the macs clock. i use usb out of mac with a usb to spdif (coax) convertor to the dac. here's the problem.

very simply in audio midi set up there are two options for controlling the dac. one reads clock source default and is greyed out. here you can alter the sample rate and bit rate. the other option is to add the dac as an aggregate device. here the clock source now reads out the name of the dac but i think you now only alter the sample rate not the bit rate. i like the fact here that the dac shows up in clock source but i am still not sure which option is correct to ensure it is the dac clock which ultimately gets used and not the clock in the computer. or am i off target here? do both of the above options lead to the dac being in full control. i appreciate your help. after many enquiries i still dont have an answer to this. why would some people use one of the above options and not the other or vice versa.

THIS IS WHAT THE APPLE WEBSITE SAYS:
"Clock source:
Leave the “Clock source” pop-up menu set to Default unless you’re using an audio device that sends its own timing (clock) messages."

The "normal" setting in audio midi setup says clock source default. only when my dac is set as an aggregate device does the name of the dac appear next to clock source. this is what i want. to make sure the dacs clock is being used as it is an expensive dac used for audio hifi through beyer dt880 headphones. so it would be okay to set the dac as an aggregate device but i thought aggregate devices were for multiple devices. i only have one external device device connected to the imac ie my dac. also i am not an audio expert by any means. here is the same query from someonelse on the computer audiophile website:

"I just purchased a NuForce U Dac2 SE that is Asynchronous. You have to forgive me if this is a newbie question, but does the internal clock of the DAC automatically get utilized? The DAC itself is working fine but the screen in the Audio MIDI setup says the clock source is: default. The Help menu for clock source says:
"Leave the “Clock source” pop-up menu set to Default unless you’re using an audio device that sends its own timing (clock) messages."
The thing is I can't seem to find any pop up menu to select clock source, Again it just says "default" which leads me to believe the macs own clock is being used. I can choose the format and set it to 96khz. I include a screen shot if that helps. Any thoughts?"
it goes on: "Just trying to verify if it's own clock is being used when connected to a Mac since the Mac lists the clock as "default" and I don't know whether that means the DACs own clock or the Mac's."

i would be so grateful if the real experts here could dig deep and find the definitive 100% correct answer to this. after nearly a year i have been unable to. the dac i will be using costs in excess of £1300.

many thanks to all.MK.

[G]

You're asking a question that's probably something most musicians never worry about (clock source), as they use one audio interface for input, and it clocks itself. For output, it's even less of a question. But as far as I know, the default setting means that the Mac is feeding digital data to the interface, which then converts the output to analog audio based on the interface's own clocking. So that should be the DAC clock. Have you tried a comparison to see if there's any obvious quality difference?

To be honest, my first stop would be at the manufacturer of the DAC. They should know for sure.