My Saffire Pro 24 Firewire audio interface has S/pdif in/out ports. My computer also has s/pdif in/out ports. My interface is already connected to my computer bia firewire. Would there be any benefit or usages to connecting the audio interface to the computer via S/pdif S well as firewire? If the answer is yes can you direct me to proper connection Protocols? Thank you, Jim
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The S/PDIF I/O on the Saffire Pro 24 is stereo. The Optical is an 8-track ADAT input.
The use case for using the S/PDIF I/O would be for using a digital stereo source or destination. You could use put an outboard digital effects processor in that loop, or say, get audio from a separate digital recorder into your computer, or bounce a stereo mix out to a digital tape recorder, etc.
Another graphic from the website:
There is no benefit to connecting your audio interface to your computer via S/PDIF if you can already make a good Firewire connection.
Some additional detail: The big problem with S/PDIF is that it lacks any form of flow control. That means that the sender sends bits out, and the receiver receives them. There is no way for the receiver to request a retransmission or even verify that all the bits are good. In practice, this isn't much of a problem, but it is a minor disadvantage compared with Firewire.
Audio over Firewire could implement flow control, error control, etc. There is plenty of bandwidth for rich control channels. The same is true of USB.
The only reason to use S/PDIF is when you have a device that only speaks S/PDIF (or AES/EBU). But if you have a high quality audio interface with S/PDIF, you are better off routing your S/PDIF signals into that interface along with the rest of your audio than into your computer.
As usual, when you have the opportunity to test out two options you should run some experiments on your own. It is possible, but unlikely, that the S/PDIF on your computer is better than on your Focusrite. The only way to find out is to develop some tests, run them, and evaluate them.