How does Apple Airplay work?

Please excuse my ignorance. I'm curious about the possibility of playing songs from an iPad/iPod to an Airplay-implemented receiver. My questions are:

1) Does Airplay work through a wifi network? Or can an iPod send a signal directly to the receiver?

2) What's the sound quality when using Airplay compared to connecting an iPod to the receiver through a USB port?

3) In a past thread in this forum, someone wrote that there was a lag when he was using Airplay. Is this common?

4) Is there any other issue that I should be aware of when using Airplay?

Thanks.

 

Don't feel bad asking!

ERm, I should know these answers, but have mostly forgotten.

A plain iPod has no way to send a signal to the receiver. I *think* and iPhone or iPod touch can, or iTunes on your computer

Apple not-too-informatively sez "AirPlay works over Wi-Fi or an Ethernet connection, or a combination of both. So you can stream music directly from your home network if you’re near an Ethernet port or connect wirelessly if you’re not."

I'm not sure if AirPlay changes or truncates the sample rate or bits (for example, my understanding is that Apple TV changes everything to 48 kHz for some reason).

 

I connect my IPod thru USB and it sounds very good. Can control it on my Plasma TV.

 

Airplay uses a network, wireless or not.

Sound quality should be the same as a direct connection since lossless is supported. I have not compared the two though.

I experience the lag also. I use Apple TV from iPad, then optical to DAC.

Airplay sucks if you have more than one receiver device. Multiple programs cannot be received at the same time on multiple devices on the same network. Stll, for what it is it's pretty good.

I use mine to stream video and for background music sometimes.

 

My recollection, and the reason I don't use AirPlay or Airport Express for hi-fi audio, is that AirPlay downsamples anything above 44.1 kHz to 44.1 kHz, so you can't use it for hi-res.

Bizarrely, Apple TV upsamples everything to 48 kHz. So if you have a hi res music file and send it by AirPlay to Apple TV, AirPlay will downsample it to 44.1 kHz and then Apple TV will upsample it again to 48 kHz!

 

Do you mean that the actual hardware is limiting this or the software? I'm confused myself to be honest. I thought there was 3rd party software which will bypass Apple whatever internal thing and output the true bit rate. Am I making a mess of things???

 

I think the problem lies not with iTunes but with AirTunes which automatically downsamples any hi res music outputted wirelessly to 44.1kHz. There's a further obstacle with Airport Express which itself is limited by its firmware to 44.1 kHz (so at least they're consistent!). You're correct that you can download software such as Pure Music which will automatically play back hi res music stored in the iTunes library at its native resolution. But Pure Music is just an audio engine - it has no capacity to broadcast music wirelessly so it will not overcome the barriers to wireless hi res playback posed by AirTunes and Airport Express. You can only obtain the digital output from Pure Music via the wired digital outputs on your computer.

If you want to play back hi res music wirelessly you have to find a way of by-passing both AirTunes and Airport Express. One way is to use any wireless router EXCEPT Airport Express in conjunction with the Logitech Squeezebox Touch. The Squeezebox Touch wirelessly pulls music files off your hard drive without ever going anywhere near iTunes, using its own server software that you install on your computer after buying the Squeezebox. It automatically plays back music files at their native resolution.

I'm a beginner though and am happy to be corrected on any of the above.