USB audio is send over the USB tot the DAC
As USB runs at a fixed rate e,g, Full Speed runs at 12 MHz, the amount of data is controlled to generate a quasi real time stream.
There a two methods to synchronise the DAC and the PC.
In adaptive mode the sample rate is guessed from the rate the data is pouring in.
The DAC has to adapt its speed to the sender to avoid buffer over/under run.
In asynchronous mode the DAC tells the PC how many data to send.
This allows for using a fixed clock at the DAC.
By design asynchronous USB allows for a implementation with a very low intrinsic jitter.
Jim Lesurf measured the DacMagic feeding it over the USB using its own adaptive interface and using the Halide Bridge, a asynchronous interface.
More can be found here
Bit more detail on USB audio
As USB runs at a fixed rate e,g, Full Speed runs at 12 MHz, the amount of data is controlled to generate a quasi real time stream.
There a two methods to synchronise the DAC and the PC.
In adaptive mode the sample rate is guessed from the rate the data is pouring in.
The DAC has to adapt its speed to the sender to avoid buffer over/under run.
In asynchronous mode the DAC tells the PC how many data to send.
This allows for using a fixed clock at the DAC.
By design asynchronous USB allows for a implementation with a very low intrinsic jitter.
Jim Lesurf measured the DacMagic feeding it over the USB using its own adaptive interface and using the Halide Bridge, a asynchronous interface.
More can be found here
Bit more detail on USB audio