I have recently bought Asus RP-N14 Range Extender (http://www.asus.com/Networking/RPN14/) with intent to use it as wireless audio connection between computer and amp. I have managed to get it running using Foobar2000 and Airfoil (no luck with dlna) but output seems audibly distorted in high frequency range. Am I doing something wrong or Asus actually managed to produce terrible sounding device in 2014?

Unless the range extender decodes and re-encodes your music or somehow incorporates D/A and A/D converters and does analog sound processing, the distortion cannot possibly come from a piece of networking equipment. Digital audio does not work that way.

papucar, it's a headphone socket rather than a line out so that could have some effect.

Should I suspect impedance mismatch?

Quote from: papucar on 2014-07-23 09:59:52

Should I suspect impedance mismatch?

No. The input impedance of your amp will be much higher than the output impedance of that unit, and that is fine. You don't want or need matched impedances for audio.

Have you tried Ed's suggestion of listening directly though headphones yet (no amplifier connected).

I am testing it at the moment but distortion seem even more pronounced while using headphones (Grado SR125).

And there seems to be heavy low frequency roll off using headphones.

That means that it has an ac coupled output, with too lower capacitance value to drive phones. Disappointing, particularly as they show a "headphones icon" on that output. But it shouldn't effect the performance when driving an amplifier.

At this stage I'd try an RMAA test on it. You can record the RMAA produced waveforms through the network device and record it on a laptop or something, and then later feed those recorded waveforms back into RMAA to analyse. It's kind of the same as a loopback test but done in two separate recording and playback phases. An RMAA test should definitively point to exactly what type of distortion you are getting.

I will certainly check it, but it doesn't sound as ground loop. Ground loop sounds like hum (at least in my experience) and this sounds like distortion.

Just want to be perfectly clear, although your original post was pretty well paid-out - you've had this distortion problem since you first used it?

And you've gone back upstream in the chain to make sure the Asus isn't being fed distorted audio?

Quote from: JabbaThePrawn on 2014-07-23 20:47:43

Just want to be perfectly clear, although your original post was pretty well paid-out - you've had this distortion problem since you first used it?

Yes, I have immediately noticed it.

Quote

And you've gone back upstream in the chain to make sure the Asus isn't being fed distorted audio?

And yes, I have checked that as well.

RMAA test will definitely confirm it but this seem to be either badly designed or defective unit. Unfortunately none of the people I know has one so I am unable to compare it other units.

Quote from: papucar on 2014-07-23 09:35:42

I will certainly check it, but it doesn't sound as ground loop. Ground loop sounds like hum (at least in my experience) and this sounds like distortion.

A ground loop just means that there is a voltage differential between the ground terminals of two devices.  Thus a D.C. potential will exist between them, which may or may not cause problems at the input of an amplifier.  The D.C. potential may vary with signals and this will introduce various forms of noise and possibly distortion.

The solution is as you say, using an audio transformer to isolate the signal. Yes it's true that the transformer does block DC, but that's not it's main purpose here. The transformer just removes the need for a direct galvanic connection between the two grounds (isolates the grounds), thus breaking the ground loop.

Another simple solution that is adequate in many cases is simply to run everything (in the system with an interconnected signal ground) from the *one* common power outlet, using a short extension cord and  "power boards" as necessary. This doesn't entirely eliminate a ground loop, but it does often make it manageable for devices that are in reasonably close proximity.