[Noumenon]

 
Of the two arrangements below,  I'm hearing noticeably more intense and tighter percussion, and generally louder sound from optical;
 
PC->Optical->CordaSymphonyDacAmp->SennHD600
 
Vrs
 
iPad->USB->CordaSymphonyDacAmp->SennHD600
 
The question is WHY would optical provide a louder and more intense sound over USB, when there is no VDC?
 
The iPad volume is not controllable with USB out, so it just sends a signal, but I can understand that it may send a weaker level signal. Would the "bottleneck" be in the Symphony DAC's internal USB->TOSLINK?

 

[Hybrys]

For one, you're using two massively different sources, and I'm guessing this is the problem.
 
For two, the average Optical i/o is better quality than the average USB i/o anyway.

 

[Noumenon]

Yes, well obviously the sources are different so that this is where the differences would originate. The question was, Why, if both signals are digital, why would one sound louder than the other, in particular, why would optical be louder than USB? The PC->USB->Symphony is the same loudness as the PC->Optical->Symphony, but the iPad->USB is lower. Maybe I have a misconception of what a digital signal is.

 

[Hybrys]

Quote:

Yes, well obviously the sources are different so that this is where the differences would originate. The question was, Why, if both signals are digital, why would one sound louder than the other, in particular, why would optical be louder than USB? The PC->USB->Symphony is the same loudness as the PC->Optical->Symphony, but the iPad->USB is lower. Maybe I have a misconception of what a digital signal is.

Some digital signals are different from other digital signals.  USB is usually the odd one out, as I mentioned.  It's peculiar and implemented in a large variety of ways depending on the receiver, drivers used, etc.
 
Plus, I said that the sources are different because they're REALLY different.  Who knows if the iPad is actually transmitting over USB @ bitperfect rates?

 

[Noumenon]

Thanks Hybrys, that's true, we don't know if iPad USB is bit perfect.

 

[brandnewgame]

It's quite possible the iPAD has some kind of software volume control acting upon the USB sound device which isn't configurable.