Airport Express - Digital audio output - and Jitter

This is not good. From what a tech guy told me at "Wyred4Sound" it's the 'Sabre' chip that will not lock onto the signal from the first and latest AEx. The middle one, he said, should be fine. Quite a few high end DACs use 'Sabre' chip.

He suggested trying an alternate player; e.g. Audirvana, Decibel, Amarra, Pure Music. I have those but like the functionality of native iTunes. I still had my 'in the wall' AEx so I put it back into service.

This week I receive a new DAC from Schiit (a U.S. company). It has a light on the front that shows if the signal incoming is bad. I hope to use that for some experimenting. In the meantime, as horrible as it is, it's good to have some corroboration. Now what to do about it, I don't know.

I found another difference between the AEx N version 2 and the newer square version 3. This time unquetionably in favor of the newer one. Here's the story.

I put the N version back in my system because the Sabre chip DAC I have would not lock onto the signal of the newer AEx - the subject of this thread. I bought a new DAC with a different chip. I was listening to the new DAC on headphones. At some point in a classical piece, a soprano held a long powerful high note with little to no musical activity beneath. Clearly then I heard a repeating knock knock knock along with the note. It sounded almost mechanical. It was rhythmic. I heard it a few times but only when constant musical activity did not mask it.

I suspected the new DAC. I made a 40 second clip of it and sent it to the manufacturer (Schiit). In a quick email turnaround he said there was no problem there. I began swapping. I bypassed the AEx and took USB out of a laptop. No knocks. I took out the newest AEx that I was not using and guess what? No knocks. Perfectly clean signal. ----

I went to another room setup I have (thank you Airplay) that has the same N version 2 plug in the wall AEx. Knocks in exactly the same places in the same way! So for the ultimate test, I purchased another new square AEx and swapped it in there as well. Perfectly clean signal.

Yup, there is an audio difference to be found tetween the two AEx's if you can isolate it. If anyone here wants the sound clip I made feel free to ask. It's a small Apple Lossless file.

So now I think the newest AEx is an improvement for the high end audio world using optical output to a separate DAC. But for the original chip compatibility problem.

Ray,

I've been tempted a few times. Did you know the ATV outputs its signal at 48k? I know nothing of high end TV audio but I think in that world of Dolby 5.1 and surround, equipment expects a 48k sampling rate. I'm pretty sure the HDMI cable receives the sound that way. But if you plug in stereo audio at 44.1k, it will be upsampled and changed to 48k. You can prove this on any DAC that shows you the rate it is receiving.

Since 48 is not an even multiple of 44.1 there have to be changes to the signal. High end upsampling stereo DACs all upsample at even numbers so there are exact doublings.

ATV has been proven to work in this situation with the new AEX. But there's one issue. The ATV upsamples the digital audio signal to 48kHz. It is being sent as 44.1kHz. They say that upsampling at 2x or 3x the original causes no artifacts to the original. But 48kHz is not a mathematical multiple. So there's that.

I imagine the upsampling is because digital surround sound etc. for TV and movie sound eqipment expects a 48kHz signal.

Honestly, I'm not equipped to know if you'd hear a difference. I haven't tested it myself.