When a computer has an optical output it usually attaches to the sound card, and uses the sound card drivers.
In contrast, when you use a USB connection, the USB DAC
REPLACES the computer's sound card (so it doesn't matter how good the internal sound card is or even if you have one).
However, because both are digital, they should sound very similar.
(Optical may have higher jitter, but is totally immune to ground and power supply noise since it's electrically isolated.)
There may be slight differences but they should really be subtle.
However, audio programs in the computer may well alter the sound to one or the other output... sometimes significantly.
Programs may actually alter the sound directly, or they may change settings that may result in dropouts and stuttering.
(And how this affects things may be different for the different outputs...)
To avoid Windows mixing and resampling, you want to use a player program that uses a Windows mode called WASAPI.
By default Windows re-samples everything you play to its default set sample rate.
And, if you have multiple audio sources, it will resample one or both and mix them together - which will often degrade the quality.
WASAPI mode "locks" the sample rate and prevents this.
Note that you actually have to tell the program to
USE WASAPI mode.
Some programs support WASAPI (jRiver Media Center and Foobar2000) while others do NOT (VLC and Windows Media Player).
As someone mentioned, the USB input on the PT-100 doesn't need drivers, and is limited to 24/96k.
However, it should sound very good if there's nothing odd going on at the computer end of things.
(Even though it doesn't use external drivers, you DO still need to use WASAPI mode to get the best performance.)
Having spent the last 2 hours cycling between USB and optical the USB is vastly inferior for me playing the same FLAC and SACD rips from my HTPC. The USB sounds muffled and not nearly as crisp.
I'm using a HTPC to PT-100 to Emotiva XPA-2 to Ascend Sierra-2
Anyone disagree? Agree?
