Very good description.
I am very ****** tonight : so far I had been using a 4y old macbook pro through tosslink for music.
Just bought a very high-end Macbook Air... only to find out it has no optical output !!!
So I'm either stuck with an analog output (no way with my audiophile setup) or this messed up airplay !
I was thinking of getting one of those usb to toslink adapter, but apparently it's not 'passthrough' so the quality would not be good for a $25 unit of so.
Anyway, just as with the iPad, I might just take it back to the store because Apple won't fix its Airplay !!
Found this on the MacRumors site:
Apple today seeded developers with the first test build of OS X 10.8.3.
Areas of focus for testing include AirPlay, AirPort, Game Center, and Graphics Drivers.
Let's hope they're working on the AirPlay problem.
Here's the MacRumors page:
I recently ran into this problem myself, as I just started using my Airport Express (1st Gen N) for wirelessly streaming audio to my iHome iP1 speaker via analog connection from my iPad and iPhone. The AirPlay audio is rock solid when playing audio from most of my apps (eg. Pandora, CNN), but it is consistenly popping when using SlingPlayer.
Thinking all the wireless streaming within my LAN was perhaps causing bandwidth issues and thereby creating the popping noises (SlingPlayer 4mbp/s inbound video and audio wireless stream on iPad + Sling audio outbound stream on AirPlay + Airport Express inbound audio stream on AirPlay), I changed my Airport Express to connect wired to my network via Ethernet. That seemed to slightly reduce the amount of soft popping sounds when using SlingPlayer and streaming audio via AirPlay, but it did not eleminate the pops.
So then I saw this bug thread and downgraded to 7.4.2 firmware on my Airport Express, and it seems to have fixed the issue. Seems to be purely a software issue with the more recent firmware builds, which Apple should be able to resolve if / when they put an engineer on it.
I'll add that since my last post, although running the 7.4.2 firmware on my Airport Express (1st Gen N) eliminated the occassional soft popping noises, that older firmware introduced a well-known bug from before: occassional dropped audio.
So I decided to test each of the firmware releases, going backwards from the latest 7.6.1 release.
7.6.1 -- frequent soft popping noises
7.6 -- frequent soft popping noises
7.5.2 -- no soft popping noises (perhaps best release to use for now)
7.4.2 -- no soft popping noises but occassional dropped audio
One other note: when running the troublesome 7.6.x firmware, the popping sounds are not present when first streaming audio via AirPlay, but within 30 seconds the popping noises begin to appear and then become more prevalent over time. This would indicate to me its a buffering issue or something related to processing packets on the Airport Express.
If this popping sound behavior exists on 3rd party audio equipment that has AirPlay networking software built-in, hopefully that equipement supports firmware upgrades!
Track from a Hi-Fi test CD:
Wide Sweep: 5 Hz - 22.05 KHz, L + R, -15 Db
I've just tried this test again with the same hardware as before, but changes in software/firmware -
Snow Leopard 10.6.8
AirPort Extreme (1st generation)
802.11n only (5GHz)
Apple TV 2nd generation - latest firmware.
Optical audio out of Apple TV is connected to a DAC.
The track from the test CD plays WITHOUT noise/distortion.
I haven't done this test for some time, so I don't know which change in software/firmware has eliminated the distortion.
I repeated the test with my old Apple TV (1st generation) with the latest firmware.
Same audio noise/distortion as before.
I can also confirm that I've noticed this 'popping' (like static on an old LP) for the last 3 years. In that time, I've swapped out the Airport Express, gone through 2 more 'main' routers in my home, 2 new Macbook Pros, a whole new receiver + speaker system, etc. And the problem's still there.
It is most easily noticed when listening to piano (glad someone else confirmed this!), probably b/c of the lack of general 'noise' (meaning louder instruments, background sounds, etc.) that might otherwise mask the popping.
I, of course, have verified that the popping is not there in the original recording. You can do this easily by plugging in a pair of headphones. The source is clean.
Also, the popping frequency increases the louder the piano is. In other words, popping appears to be directly related to amplitude of signal. The louder the piano gets, the more pops there are. Source file does not have any pops though, & the WAV file shows no clipped waveforms.
Audio files of just silence don't pop at all.
Airfoil pops even more than iTunes/OS X built-in AirPlay. Airfoil's popping is also correlated with amplitude of signal (how loud the song is).
Fascinating stuff. The correlation with volume makes me think this is probably a relatively easy fix.
This problem appears to be solved (at least for me) in the latest Apple TV with the latest software. However, I have noticed it in the new Pioneer SC-1223-K receiver with Airplay onboard. If you use the built-in Airplay the infamous clicks are present. So, apparently, there is some kind of firmware issue with hardware (Airport Express, Airplay in AVRs) that causes this? Not sure but that seems the most likely explanation. I think it's embarassing for Apple that years after I started this thread, the problem is still ongoing in their own as well as licensed hardware.