Airport Express clicking sound

I'm hearing a clicking or popping noise when using my Airport Express. It only happens on very "pure" sounds, like a high trumpet or a high soprano. Perhaps it is occurring other times but I can't hear it then.

I'm going from iTunes on a laptop to the Airport Express, digital out to a DacMagic. I know it's not the DAC, as I burned the same files to CD and played it through a CD player hooked up optically to the DacMagic, and no problems. I also tested the same files going directly from an iPod Touch to the Airport Express.

The only other thing it could be is the router, but I don't have a second router to test with. Any ideas of what's going on?
I should clarify that when I tested the same tracks going directly from the iPod Touch to the Airport Express, it was still going through the wireless network, and the clicking/popping sounds were the same as when the files are fed from the laptop.
Your DAC may be clipping.

Steve N.
Empirical Audio

Thanks for the input. How can the DAC be clipping if when it is fed the same signal from the CD player, it doesn't clip? It only "clips" when the signal is coming from the Airport Express.

Very curious to hear more about a clipping DAC, Steve. I'm getting "skipping" (interrupted signal, different places in songs on different plays) while using my Perfect Wave DAC since upgrading to the MK II board (only with computer as transport, not CDP).

I updated the system, version of iTunes and added memory on MACbook, but problem persists.

Any suggestions appreciated.

Jdoris - skipping is usually caused by the playback software and hardware. The latency is too large for it to keep-up. This can be caused by network congestion if you are using the bridge, or by competing applications on the computer, or slower front-side-bus and small DRAM size with USB.

Which interface are you using on the PWD?

Clipping is usually indicated by ticks on only the louder passages and transients.

Steve N.
Empirical Audio
I had dropouts from time to time on Airport Express digital outs but it stopped after I installed stronger 802.11 transmitter (USB adapter) setting it to transmit on 2.4GHz and 5GHz simultaneously (AE listens on both by default). I don't know if AE receives anything on 5GHz (my router is only 2.4GHz) or is it better transmitter (MacMini has just short piece of wire for antenna inside), but dropouts are completely gone. MacMini's internal Wi-Fi transmitter (Airport) is disabled (won't work with two networks). Dropouts were just gaps lasting 1-2 seconds and not clicks. AE has about 2-3 second buffer judging by amount of time it plays after shutting down transmitter.
Markhyams: I had something similar when I first hooked up my computer. I thought my computer out had too much gain??? I don't know if that's the correct terminology but when I lowered the output volume on the computer to %75, the noises went away. Go in your settings and try that.
Devilboy - lowering the digital volume is never a good idea. Good thing to avoid unless you want to lose all of the good things in the music. about -9dB is the most you ever want to reduce volume digitally.

Steve N.
Empirical Audio
Thanks Steve!

PSA suggested I approach the skipping as a PC problem, so I: upgraded the system in my MACbook, updated to latest Itunes, put in new memory (8GB), and replaced the external drive on which I store my music. I also did an activity search, to make sure other programs were not running and interfering.

This did not help, nor did swapping out USB cables, so I remained suspicious of the DAC, especially since the problem started when I installed the PWD MKII upgrade.

I therefore obtained another DAC (PSA DL III) and switched it into the system -- that appears to have resolved the problem.

I suspect it is something to do with the USB in to the DAC, since the problem did not occur when I connected a CDP transport via coax.

Curious if you have any further thoughts; I'll be in touch with PSA presently.

Update: I replaced the Airport Express with a Squeezebox Touch and the problem disappeared. Clearly something was going on in the playback chain with iTunes and the Airport Express. What that something is, I don't know. Interesting to say the least, as the AE is purported to be "bit-perfect." Now with Logitech Media Server and the Touch, all is well.
Your computer or the AE could have been locking into a legacy and/or overloaded WIFI network.

I had a similar problem recently, but the cause was far more obvious... the noise started right after I replaced my generic "had it laying around" optical cable with a fancy new optical cable that turned out to be defective or was damaged during shipping.
Your computer or the AE could have been locking into a legacy and/or overloaded WIFI network.

But I have the same wifi network and the same computer running Logitech Media Server.

I really think something was going on with the AE, although I never tested it with its analog outputs.