[noxa]

I've been wondering this for a while now, a pretty simple question I would have though, say I use the line out on a cheapish Fiio X1 will it be the same as using Line out from a high end player? As the internals are bypassed is the player simply a UI and transport of using a true line out?

 

[Ruben123]

Yes usually

 

[castleofargh]

first you need to make a difference between digital out and analog out.
the X1 only has analog out and headphone out, no digital out. so it can't possibly bypass the DAP and be what we tend to call a "transport", sending only the PCM stream of digital data to an actual DAC+amp of your choice that will have to do all the leg work.
no the analog out like on the fiio X1 isn't the same as any other line out and doesn't send the exact same signal. you can make a caricature saying that an analog line out, is the signal output with the settings that offer the best signal possible for that given device(so pretty much the X1 with volume maxed out in this case, plus a change of impedance). so it's still very much the quality the DAC section inside the X1 is capable of with specs limited by the X1. it's very good signal, but not perfectly identical signal compared to another source or DAC. 
 
now on the audible side of things, because the X1's line out outputs the best signal the X1 can create, the signal ends up being very good. and the perceived differences are usually small or inaudible. smaller than changing the amp section, and smaller still than changing the headphone. that's why using even an average source with a line out is usually a reasonable way to get good sound.
 
now if you were talking about actual digital output, and a DAP capable of behaving as a transport, then yes the signal sent should be 99.9% identical and entirely processed by the external DAC+amp. the 0.1% could be some jitter, noise coming from the transport and reaching a not shielded enough external DAC... small stuff that shouldn't have much if any audible impact as long as the external DAC is well made and the transport can use the best possible transfer protocol for the DAC(some will simply not work at all).

 

[noxa]

^^ Thanks for such a detailed reply, so basically digital line out is the same across the board no matter what as all the device is being used for is a vessel for the content to be supplied to the outside party being the dac and amp. Whereas an analogue line out will still be tainted to a certain degree by the internals of the device in question?

 

[castleofargh]

that's pretty much the idea. but know that you can find people who think the transport impacts the sound a lot, just like you have people like me who believe even the DAC part going into an external amp only have a very minimal impact on sound, and a transport pretty much none at all.
so maybe don't take my word for it. I did try a cellphone that sounded like crap into my external DAC/amp, and I have no idea why. but using my tablet or my laptop, it makes no audible difference to me. so I tend to think that the cellphone was a lemon with a specific problem.
 
measurements would tend to agree with what you just said. there are very little reasons for the transport to change the signal in a meaningful way.

 

[ProtegeManiac]

Note also that not all analogue line outs are equal. Forget circuit topology, not all follow the Sony Redbook-spec 2volts. If you get two sources for subjective evaluation they can both measure the same but one outputs 2.2volts and the other 1.8volts, and if you don't adjust the setting on whatever amp you're using, the former usually sounds better.

 

[castleofargh]

very good point. most portable devices are more around 1V than 2 in practice. while home systems are more and more between 2 and 3V.
as portable stuff I own, my extremes right now are the fiio X1 with an analog out of about 1.5V, and my sony that is somewhere around 0.25v I think(I've measured it somewhere but .... where? ^_^).
so yes the loudness of the analog out can make a sensible difference(noise floor and gain setting are another mater that may or may not need adjusting, but it can be good to know before buying).

 

[watchnerd]

Right, not all line outs put out 2V.