What is better quality audio digital or digital optical?

Answer 1

The question probably refers to a copper digital interface against an optical interface. The copper interface carries electrical signals while the optical interface uses light pulses to carry the signal. The quality of either of them is dependent entirely on the quality of data that is fed to the interface. A copper cable or an optical fiber carrying the same data will deliver identical signals at the far end. At high data rates fiber can generally carry a signal a longer distance than copper but at audio rates, this is not the case. There are a few audiophiles who claim that copper cables can cause "jitter". This is a minor instability in signal timing and in extreme cases it can result in lost data. Their claim is that jitter causes audible distortion although there is little evidence to support the claim. Almost all equipment use techniques to eliminate the effects of jitter. It is also the case that optical fiber links suffer from the same jitter. Although this answer is not intended to fuel the debate about jitter distortion, one should be careful about how much weight is given to the "jitter causes distortion" argument. Therefore, when selecting a transmission method, the most convenient link should be selected. If both source and receiver have optical links, use optical by all means. If both have a copper digital link, that will operate just as well.