I’ve been tinkering… Apple Airtunes is pretty slick

Many folks are familiar with Apple Airport Express and Airtunes. It provides the ability to send iTunes audio from a PC/Mac to speakers that are connected to the Airport Express (which has both a Toslink and a line-level output). I’ve been playing with the latest variant. With Airport Express w/ wireless N, they’ve added the ability to support simultaneous receivers receiving the same content. What I call a point-to-multi-point topology.

I’ve also been playing with Rogue Amoeba’s Airfoil which lets me not just play iTunes music, but ANY music from any app on my Mac, or wait for it… a Windows PC. I also have been using Airfoil Speakers which lets me turn any PC, Linux box, or Mac in my house, to an Airtunes receiver. A little tray app runs on that PC, and makes it look like a Airport Express, for example.

I’ve heard Airfoil lets your send music to Apple TV as well, though I haven’t been able to test that. I assume it’s as robust as the others have been… and with that little bit of foreshadowing…

It really works well! I love it actually. About my setup:

Audio source:

1. My Macbook Pro running all manner of audio… iTunes, Pandora, Slacker, whatever…

Receivers:

1. My iMac running Airfoil Speakers
2. Airport Express-1 hooked up to Bose SoundDock Portable
3. Airport Express-2 hooked up to Bose Companion 5s.

So a little about Apple Airtunes, which is Apple’s proprietary protocol for sending compressed audio over WLAN (AoW). This is all reverse guesstimated based on what little I know about wireless audio…First of all, I call it AoW… I hesitate to call Airtunes “wireless audio”, because it only appears that “audio” is being sent wirelessly… what is actually being sent are chopped up AAC (correction via mats) Apple Lossless “data” files with a whole bunch of QoS goop wrapped around it. Strictly speaking, Airtunes relies on a non-linear, asynchronous packet-based transmission scheme, TCP-IP over WLAN. What Apple has created is an extremely broad time-window for synchronizing audio data, creating isochronous behavior using asynchronous foundations and lots of software… that’s why you need devices running Apple smarts on either end. Airtunes basically estimates a total time buffer need based on network utilization and bandwidth requirements… creates a time-stamp on the source material… encodes both the stamp and the buffer-time in the data stream… Marker “A”… then it takes the audio data… compresses it on the host side, then essentially transmits the compressed file plus meta information… performs the network transmission, decoding… audio decompression, and again recovering the time stamps and synchronizing them to the device clock and then upon reaching the target time marker extrapolated from the buffer-time… begins rendering the audio at… marker “Z”. Or something close to that… I think…

All-in, what Apple does are three important things:

1. Prevents audio dropouts due to periods of reduced network throughput… i.e. it behaves as a buffer. This is important since the WLAN network is a shared network and throughput for audio is not guaranteed.
2. It makes sure all the nodes are playing music in sync to one another, and without time-varying node-to-node drift… This is important in whole-home audio scenarios to reduce echos and unnatural artifacts.
3. To the extent A-to-Z can remain fixed over a playback period… Airtunes also can avoid any audio discontinuities during playback. If the buffer was well-estimated at the beginning of a transmission, then you won’t have to resize the buffer and suffer a “skip”. One advantage of Airtunes is it can be content aware on the source side, and know when there are silent periods and take those times to reset buffers if need be. Not sure they do this or not.

The result. Fairly rock-solid performance for up to 3 nodes spread across a 80 ft radius space.

Pros

• Apple has been giving much of this functionality for free to those who already buy up Apples stuff. The “converted” are very close to having this stuff working for them.
• Apple software rocks. So this stuff really isn’t THAT hard to set up. A little easier than say setting up a WiFi network. A bit harder than hooking up a TiVo. By PC standards… not bad.
• Sound quality and link performance are generally great. For that party mode performance, it works pretty well.

Cons

• Compared to setting up piece of CE equipment, it involves much too much PC time. Installing software, control panels, SSIDs, etc… Advnaced PC user know-how is a must. Even by Mac standards.
• Poor marketing… did you even know this was possible…???? Today???? Like all things, Apple likes to Trojan horse features… then once they get them shaken out by geeks like me, they rationalize them in to shiny new products and services that Stevie J can launch… MobileMe anyone???
• Delay Delay Delay. Buffering and buffer management is the magic to Airtunes… but oh how clumsy it is when you want to adjust volume, or change track… User have to check their audible feedback expectations. Usability nightmare. And what was strange was the more I use this system… the more I notice the delay time…. and of course the more it annoys the shit out of me.
• Cost!!! If you aren’t a Apple hardware dork yet. Be prepared to dump $99 for each Airport Express. Add to that the cost of the speaker system you need to connect to it. Rogue Amoeba software is a great convenience, but it ain’t free… not bad though to be honest. Airfoil is about $25 per seat. Airfoil Speaker is free… but the computer it runs on is not!

Overall Grades:

B+ for Apple – for giving us a platform

C for Airtunes – for working ok, but using WLAN… a terrible, terrible transport.

A for Rogue Amoeba – for exploiting a platform to the fullest and making nice software that just works.