Airport Express/Streaming Audibility Tests

They aren't Paul it's just misdirection for the fact that they are incapable of keeping a network lock and have too small a buffer fitted to cache sufficient audio data.

They are simply flawed.

Rob, it's not a case of what you think about a track being good enough, it's about removing confounding variables from your test results. If you want to use these as justification for a particular viewpoint once the results are in then you really need to be applying some rigour to the selection of all parts of the test.

Using a track with significant background noise and another with is entirely synthesised and therefore contains no natural acoustic clues is hardly a fair pitch. Just use the best recorded cd you can find, not the most obscure crap.

 

I don't think what you say is accurate Simon. Stability has to be achieved. The Aex runs for a period then corrects its signal rate by a rapid correction. Other devices drift slowly one way and the other around a central mean.

I don't think it's anything to do with buffer size, or a fault in the Aex. Nearly everyone in the world finds them to be excellent. It's just a few dacs that can't track the signal properly. Most of the small number of makers of the troublesome dacs have eradicated the problem including Cambridge.

I just think that Simon doesn't want to accept that view, and there are others who think similarly. The overwhelming weight of evidence from world-wide use says differently though. imo.

JC.

 

Rob,

I appreciate the offer to do more blind tests with the AEX, but my first priority is saving for a new cartridge (I'm really due for a new one), then for 301 restoration, so any foray into computer audio is quite some months away.

I'll admit that the analogue out on the AEX was OK and better than I expected, but it's not amazing and I doubt if it's equal of the analogue out on my CD player. To do computer audio right I think I'm looking at a headless Mac mini plus a decent DAC.

What I would be interested in hearing is a CD player vs computer + DAC comparison  a couple of digitized files from, say, a CDS-II (or similar good CD player, doesn't have to be a Naim) vs. digitized files from, say, a Mac mini into a respected DAC (Weiss, Benchmark, Naim, whatever.)

I realize this is a lot of work for you, so don't do it on my account. I'm just saying that that's the sort of blind test I'd like to try.

Joe

 

Although I haven't measured it, I think the Aex, when playing from iTunes, forwards no signal during silence. i.e. it transmits nothing = the digital stream ceases, and rate corrections occur even at intervals of a few nano-seconds, and seemingly randomly.

Whereas Airfoil transmits continuously, just transmitting zeroes or something like that so the transmission rate is kept at the correct average by drifting it from feedback applied with a long time-constant.

imo



JC

 

That reminds me of the old argument used many years ago that only classical, or what was deemed to be 'serious' music was good enough to demonstrate hi-fi.
It's a nonsense argument IMO.
Many old and loved Blue Note recordings for example have very obvious hum, hiss and cracked pitch due to flutter in the tape drives of the day. This doesn't stop them being pressed onto modern 180gm vinyl and passed around as examples of wonderful sound, and i'm certain people compare kit using them, or the CD issue.

But have no fear, you shall have your wish tomorrow.
I have just the thing.

 

I could do Mac/dac V Meridian 206 (same chipset as the Naim)
Plus Meridian transport/Dacmagic V Mac/Dacmagic.

I'll PM you some stuff over the next few days.

 

Rob,

Thanks for that.

But if you're going to the trouble of a test, wouldn't it make sense to open it up to everyone? I can't imagine I'm the only one who's interested. And for all we know, it might even convince JC to come back to the world of legacy hi-fi.

Joe

 

Can do, perhaps once this AE experiment is concluded.

Meanwhile.....

Here are two more tracks. Full fat audiophile quality stuff. I've even called them SQ

See what you think:

SQ - A http://www.mediafire.com/file/cg0kc6776ztxcr3/SQ A.wav

SQ - B http://www.mediafire.com/file/esyhehgrhk9p85p/SQ B.wav

 

Rob,

I prefer SQ A to SQ B, but B is louder.

I tried to compensate between tracks by adjusting the volume manually, using the volume up/down keys on the keyboard, but I probably didn't match them perfectly and I may have inadvertently biased my preference toward one file.

As in the other tests, I thought A had more zip and dynamics, with B a bit meandering and squashed in comparison. Again, not night and day, but I hear a difference and definitely prefer A to B.

I'm curious to see if I got this one right.

Joe

 

I'll have a listen later today. Sounds interesting.

 

JC, I accept that the AEX does not transmit an 'in-spec' Spdif stream all the time, and I also accept that manufacturers have been able to work around this.

The difference is that i see this as a fault with the AEX, and you see it as a fault with the multitude of DACS that work perfectly with every other device ever made.

You see the difference?

 

Simon, there is no requirement in the s/pdif spec for transmission 'all the time', - in fact it would be a big problem if you weren't allowed to stop and start the stream as desired, particularly in professional use. It is after all a subset of AES/EBU.

The requirement for dac muting, when the stream starts and stops, or re-starts, and re-lock occurrs is almost universally implemented in good dacs nowadays.

I just wouldn't use a dac which didn't have that facility.

To have big pops occur when switching sources or streams is clearly un-acceptable and this is clearly a fault of the dac, not of the source.

I don't want to touch on a sensitive issue, but it's one of the reasons why I think the dac in the 9's is so good, - and therefore why I choose it for use myself. You can switch sources on the same input, or switch between inputs, or stop and start the stream, ... and pops are completely absent. This is how it should be. There is no need to put up with kit that can't handle this situation. imo.

Turning to the Aex, - the new ones do correct the stream rate very fast and abruptly, and some dacs lose the lock as a result, and issue pops and chirps when they re-lock. This is clearly a problem of the dac, in that it doesn't re-lock fast enough.

Most dacs don't have this problem and work correctly. My solution to the problem is to dump the dacs that don't work properly and get one that does. This is what I did in the case of my Apogee dac. I understand the later Apogees don't exhibit this defect.

If, in your case, if you think that the whole of the rest of the world should alter, just to fit in with your particular 840c, then I think that is an un-realistic scenario. You should try and come to terms with that.

JC.

 

Meanwhile, back to the topic, .......

I've just had a quick listen on speakers ...........

The differences are not great, to say the most ..............

However this time I preferred A. ........... let's say 3A on Rob's scale.

I thought that B had bass which was a bit muddled and boomy but the rim shots were good again.

A seemed to have cleaner bass lines .......

Maybe it's just imagined factors which are triggered by the musical content of the track.

However I think that if I heard B as a track in isolation, I think I would say that the bass is a bit muddled and boomy. I rather think this occurred as a consequence of the recording, or production technique.

JC.

 

I can do a Squeezebox Receiver capture later today when the ADC has warmed up. As a GBP100 network player this is a similar sort of functionality to the AEX albeit without the random rate changes.

Paul

 

One of those might suit Joe.

I tried the earlier squeezebox stuff but found it to be unreliable. People tell me it's better now it's made by logitech.

I also didn't think the sound quality was up to much and there was a growth of small firms who charged several hundreds of pounds, and claimed to be able to modify them to bring the sound quality up to standard. Patrick Dixon of @-Tunes being a case in point.

Here's an extract from Nick Whetstone of TNT Audio.

" Originally, Patrick Dixon of @-tunes came to see me with his own music server and SB+, and I had a brief listen. Unfortunately, that morning I had hastily connected up my speakers with one of the drivers out of phase so it wasn't the best of tests. However, it was enough for me to realise the potential of the SB+ and agree to write a review. With speakers set up correctly, and my own music server in place, I looked forward to putting the SB+ through its paces. Patrick kindly helped me set up the network connection, and gave me some tuition on using SlimServer. As ever, these things look much more complicated than they actually are. But it is fair to say, that getting all this set up, particularly ripping the music to the hard drive, is a bit of a learning curve. So is it all worth the effort?"

I came to the conclusion that it definitely wasn't worth the effort and expense, and preferred the simplicity, excellent sound, and ongoing R&D, of the Apple AirTunes system. (Now AirPlay with the new AppleTv which replaces the Aex in practical terms)

I haven't bothered re-assessing squeezebox stuff recently, but I don't think I want to use it anyway.

JC.

 

I agree that for us folk using external dacs this can be seen as fault. It certainly isn't desirable. For the main product market using the analogue output it wont be an issue.

Best advice is to check that you are happy with the AE and your particular dac. It works well enough with many.

 

Please do Paul.

No reason why we cannot broaden the thread to include other devices, and also amend the thread heading to reflect that if need be.

I'm intending to capture the SHQ Prom feed tonight and wil make it available for download. Big file though.

Rob.

PS: files levels now matched. Stupidly didn't do it last night (or rather at 4 am today) - multitasking has its drawbacks when dog tired

 

How do you level match them, with an 'amplify' or 'normalize' transform?

 

I can grab some from the HD broadcast. Might make an interesting comparison.

Paul

 

Rob I can't pick anything as being really different with them. if pushed I'd say i prefer B, but feel I would struggle to chose it in an AB with any accuracy.