Noisy digital connection from Airport Express to DAC

[Kumar Kanetkar]

If this is a repeat, sorry, please someone point me to the thread where this may have been covered already.

 

Existing system - Marantz KI Pearl lite SACD player driving high end equipment/speakers.

 

So far I have had excellent results playing lossless files from my ipod, connected from its dock connector to an ipod socket on the front of the Marantz. I suspect that is a digital connection, and the Marantz DAC converts to analog and then feeds the amplifier. Regardless, I am not able to make out much of a difference in this, compared to playing SACDs through the Marantz.

 

I have recently bought an ipod touch, and want to play it wirelessly in this system via an Airport Express.

 

I set up the AE, connecting it using a Toslink to the digital optical input socket of the Marantz, and it is successfully streaming audio from the ipod as well as itunes in a mac, to the system, both music as well as streaming radio. But there is a crackling sound in the speaker - not loud, but audible just above the noise floor, from the speakers. Other than this, the sound quality seems to be just as good as in the other modes.

 

I get clear, noise free sound when I play streaming radio from the i pod touch to another amp, via a cable. So the wifi network seems to be able to do this, providing a distortion free internet radio signal to the ipod touch. Even where the signal is weak, rebuffering stops happen once in a while, but when the stream resumes, there is zero distortion or noise.

 

Given the above - what might be the problem? As I see it, it can only be in the AE, or in the toslink connection to the Marantz. Correct?

 

Any guidance on next steps would be very welcome and appreciated.

 

Thanks in advance.

 

[nigel]

If you can get hold of another Airport Express, I would try swapping them to see if you can still hear the problem.

 

I once had a similar problem - I would hear a buzzing noise when certain frequencies were played. It sounded like something was loose in my loudspeakers. I swapped the speakers and the amplifier before I finally tracked the problem to the Airport Express, which I swapped for a different one (I own several). Since then, the system has not had a problem.

 

[Kumar Kanetkar]

Thank you for the input.

 

The problem seems to have fixed itself after some work, though I am not sure why, so I am not quite comfortable. But if it stays that way, I am not complaining...

 

I tried out the AE with an analog cable in another location, and it worked fine, and this ruled out defects in the AE, almost certainly.

 

I then reconnected AE to the main amp, using the same Toslink connection - and now there is no static.

 

I hope it stays that way.

 

[mleghorn]

Just to help isolate the problem, I would try using the audio out from the airport express -- you might even be able plug headphones directly into it (headphones must have a stereo mini plug). If you still hear the problem then you know the problem isn't introduced into the digital signal being sent to your DAC/amp.

 

Also, as a side note, I tried streaming from my iPod touch directly to my airport express. I noticed that the sound quality isn't as good as streaming from iTunes on the computer. After closer comparisons, I concluded the when streaming from the iPod touch the music is somewhat compressed and the sound stage is reduced. I suspect the bit-rate is lowered in the streaming from the iPod touch to the airport express.

 

[Kumar Kanetkar]

I have realized now that as long as the speakers are putting out decent sound, I am not able to hear the differences that audiophiles do - not referring to static of course, that is clearly heard even by me. This inability actually makes life easier!

 

My only concern therefore about direct streaming from the touch, which has the advantage of being able to leave the mac out of the loop completely, is battery life of the little device. Putting out a wifi signal must draw down the battery a lot quicker than using it as remote to control itunes streaming, when the mac does the heavy wifi lifting, is what I am guessing.

 

On the subject of the non audiophile ears, here is where things stand currently for my bedroom set up where the mac sits on a long desk alongside a Denon M38/Spendor S3/5 system. Because of constraints, I am only able to keep the speakers on the desk, and not on stands. I have done what I can to help them, by keeping them close to the front edge of the desk, 18 inches between them and wall behind them. They are mounted on vibrapods, to keep the resonance away from the desk, which is made of wood anyway, and therefore non resonant.

 

I was/am thinking of playing the mac through the stereo, using a DAC, the Denon doesn't have a USB socket to receive signal, of the kind the Marantz Pearl has at the back. The Denon also does not have any optical in. Which is why, thoughts of a DAC. But before I did that, I tried connecting the headphone socket of the mac, to the aux in of the Denon, using ordinary analog wire terminated appropriately at the two ends. And all I can make out as difference in sound is a little reduction in the sound output. The comparison is to the sound level that I hear, when I plug in a ipod to the front of the Denon, where there is a USB socket that can be connected to the 30 pin output from the ipod. Since the Denon has made for Ipod markings on it, I assume that this is digital output too, converted by the DAC inside the Denon.

 

I still have to try an A/B comparison, which is easy to make from the remote of the Denon via the source button on the remote, with a CD playing in the Denon, and the analog wire from the mac headphone socket.

 

If all that I still hear in that is sound level difference, it would seem there is a cheaper way to fix this, by using the Denon volume control button, than buying a DAC! And the mac certainly doesn't inject any static, so if it does bad things, these are the mysterious to me things like jitter/timing and other stuff. So for now, unless I hear something very different/better when I play a CD in the Denon, I will firmly resist the temptation of buying said DAC.

 

I am coming to believe that given a distortion free source, all that my ears can then perceive as sound quality differences are driven by three things:

 

1. The quality of the speaker

2. The speaker placement in the room

3. The room acoustics, which interacts with speaker placement as well.

 

Since sound isn't heard by the ears, which are mere transmitters, but the hearing happens in the brain, there is also a fourth factor, which isn't as silly as it sounds. And that is I hear better sound after downing a glass of whisky!