I ain't dropped acid in over 20 years, so why the audio flashbacks now?

March 22, 2008 1:35 PM

What is probably a very naive question about stream audio ...

Mrs Mutant and I are blessed enough to have a Macintosh running OS X in every room that matters. All connected through two wireless access points, one downstairs an ADSL modem / router that basic internet connectivity, as well as NAT and DHCP for authenticated clients. The second is a simple repeater that extends our coverage of our LAN up to flat's second floor. The repeater is physically connected to the ADSL modem via ethernet cable. We run WPA on both access points.

The question is this: we like to listen to streaming internet radio and typically will have all the Macs tuned into the same station (Soma is a current fave). Latency, however, can be a killer. Specifically, it's not uncommon for the Lounge and Kitchen iMacs - a 1.83Ghz Core2 Duo Macintel and G3/333 iMac - physically separated by less than three meters - to play the same station, same music, out of synch by a good fifteen seconds or so and sometimes longer. We're using iTunes on all Macs for client sw. Its disconcerting, to say the least, to hear music so markedly out of sync.

What gives? I'd read years about multicast, and it seems that this (sometimes extreme) latency shouldn't happen if this protocol were indeed used. So can we assume multicast isn't being used by the client sw?

It's almost as though each Mac has a distinct session between it and the server, and is receiving a unique audio stream, but that's my conclusion just looking at behaviour, and perhaps is wrong.

Also, can anyone suggest a reasonable client? We've got two Macintels, but also G4 and G3 class machines. And the Macs used up in the back bedrooms are G3 iBooks with limited RAM and small hard drives (we're frugal, but they're cheap and sound great driving USB speakers) and won't run Java that well, so Slimserver on one of the fast Macintels driving the slim sw client on the G3s are out.

Many thanks for your help!

posted by Mutant to technology (5 answers total)

It's almost as though each Mac has a distinct session between it and the server, and is receiving a unique audio stream

That could well be the case. Are you using iTunes as the client for the internet radio?

Airfoil is a product that can take one audio stream and send it to multiple computers/devices, keeping the audio in sync.
posted by dereisbaer at 2:20 PM on March 22, 2008

"Are you using iTunes as the client for the internet radio?"

Precisely. Each Mac hosts it's own copy of iTunes and runs it locally.
posted by Mutant at 2:27 PM on March 22, 2008

Seconding Airfoil. It's designed for keeping multiple computers/speakers in sync.

Added bonus: if you want to change the station, you only have to do it on one computer!
posted by wyzewoman at 2:52 PM on March 22, 2008

Multicast is not used on the internet at-large.. your ISP and your favorite streaming radio won't support it in any way.

Multicast is used on the internet at the backbone level for exchanging routing information, and by private networks internally for some types of content distrubion, but as a general internet technology - it's not something content providers can use.
posted by TravellingDen at 4:58 PM on March 22, 2008

as an alternative, VLC can restream things multicastily if you want. (you can do this on your local network - on the Internet, not so much.) definitely not as easy to use as airfoil, though, but it is free (and handy to have anyway as a media player). the iTunes radio streams are definitely not using multicast - really, you're running X independent streams from the server (where X is the number of computers) which get out of sync due to latency/buffering/etc, and it's not any different from going to soma.fm in your browser and clicking the Listen links.
posted by mrg at 7:17 PM on March 22, 2008