Airtunes "multicast" not an option - why?

Posted:
in iPod + iTunes + AppleTV edited January 2014
Thrilled at the news of Airtunes. I have all msic on a g4 tiBook connected by wire to hifi. I thought Airtunes would allow me to connected other hifis around the home to my wifi network (which it does), that I can create each room as a zone (which airtunes allows) and that I could play on ALL hifi's simultaneously - a multi-zone zone.



But I'm given to understand thatg Airtunes doesn't allows for "multi-cast" to more than one room or hifi or even other Mac at a time. One reason posited for this is one of "synchronisation", however this doesn't make sense to me.



Does anyone know why airtunes doesn't deliver this most obvious and desirable function? How much of a technical hurdle is this? Is it on Apple's roadmap? I can't beleive it isn't.



Also, a related question - I have Harmon kardmon USB speakers - can I connect these to the Airport Express widget?



Neil
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Comments

  • Reply 1 of 25
    eugeneeugene Posts: 8,254member
    Practical limitations of 802.11g bandwidth. When you have two wireless clients talking to each other it's bad enough, add multiple simultaneously connected clients and it probably doesn't work too well.
  • Reply 2 of 25
    Quote:

    Originally posted by Eugene

    Practical limitations of 802.11g bandwidth. When you have two wireless clients talking to each other it's bad enough, add multiple simultaneously connected clients and it probably doesn't work too well.



    Hi Eugene,



    I have 11mb/s wifi - I forget which flaour of 802 that it. I have iTunes set to stream at 128kb/s. This is a tiny fraction of the available bandwidth - even multiple streams of 128kb/s is inconsequential - I need 3 maybe 4 lots of streaming simultaneously - this would be 512kb/s - surely my wireless Ethernet network can support this?!



    Neil
  • Reply 3 of 25
    Quote:

    Originally posted by neilfairbrother

    Hi Eugene,



    I have 11mb/s wifi - I forget which flaour of 802 that it. I have iTunes set to stream at 128kb/s. This is a tiny fraction of the available bandwidth - even multiple streams of 128kb/s is inconsequential - I need 3 maybe 4 lots of streaming simultaneously - this would be 512kb/s - surely my wireless Ethernet network can support this?!



    Neil




    I believe that Airtunes uses Apple Lossless to stream between the Mac and the Airport Express station... that weights a lot more than MP3 or AAC.

    I'm not sure about that, though, gonna check!



    EDIT : can't find anything about the format used for streaming from the Mac to the Airport station. If someone could help me here...
  • Reply 4 of 25
    eugeneeugene Posts: 8,254member
    Whatever it is, it's going to have overhead. In addition it's going to have to deal with real-world performance of an 802.11 network. If you have a mixed network and a "G" device that is more than 50 feet away in a regular house...good luck...
  • Reply 5 of 25
    davegeedavegee Posts: 2,765member
    Well it pretty much comes down to one of the following reasons:



    1 - Apple didn't think of this feature (not likely but...)

    2 - Apple did think of this feature but due to 'whatever' couldn't get it working reliably. (more likely...)

    3 - For the future hardware fans (you know who you are) - Apple has another larger project in the wings that will do this. (just had to throw this one in).



    So one of the following will be the final outcome.



    1 - Apple will add it in the next release

    2 - Apple will try and work around the 'whatever' and post an update when they crack the problem. If they can...

    3 - Apple will release 'some other project' when the time is right - sometime just after we all get the Airtunes and they are no longer returnable would be my guess...



    Dave
  • Reply 6 of 25
    Quote:

    Originally posted by Eugene

    Whatever it is, it's going to have overhead. In addition it's going to have to deal with real-world performance of an 802.11 network. If you have a mixed network and a "G" device that is more than 50 feet away in a regular house...good luck...



    From memory, Ethernet in a typical LAN delivers at best 80% actual throughput of "standardised" spec - thus a 100Mb/s Ethernet network will crap out at 80Mb/s utilisation.



    On this basis I actually have >8Mb/s - even if it was 5Mb/s or even down to 2Mb/s actual throughput - there should still be plenty of bandwidth for multiple hifi over wifi channels. OK, so there may be an overhead, but just how big does that need to be - even in a "lossless" environment? As for distance- everything is easily within 50ft of the basestation.



    Don't see what the issue is.



    Don't understand:-(



    Neil
  • Reply 7 of 25
    davegeedavegee Posts: 2,765member
    Quote:

    Originally posted by neilfairbrother

    As for distance- everything is easily within 50ft of the basestation. Don't see what the issue is.



    Well... first one can't assume everything is going to be within 50' of the BS and second even 10' can SEEM like 100' if say you're in NYC (or some other concrete jungle) with concrete steel reinforced walls. I know quite a few people at work who live in NYC and require 2 BS to cover their 2 bedroom high rise apartments.



    Dave
  • Reply 8 of 25
    hmurchisonhmurchison Posts: 12,289member
    Totr is correct. Before the audio is sent to the airport it is transcoded to Apple Lossless because the Airport doesn't have any processing in it and your stereo needs either analog or full 16bit 44k didgital data. Once people have stereos that can support AAC natively this might now be such an issue.
  • Reply 9 of 25
    aquaticaquatic Posts: 5,602member
    Yes it'd be cool if they used whatever chip they have in the iPod and put it in the AirTunes module so they wouldn't have to upconvert a tiny 128kpbs MP4 or MP3 to Apple Lossless which is much much larger. Wouldn't that be a solution to this problem? This issue would prevent me from buying AirTunes. If they could solve this perhaps like in the way I mentioned above I'd consider getting one.
  • Reply 10 of 25
    this is quite a bit off subject...but I have to ask...has anybody tried extending a third-party 802.11b signal with the Airport Express?
  • Reply 11 of 25
    eugeneeugene Posts: 8,254member
    Okay, so Apple lossless is anywhere from 75-125 K/s average and that's with lots of peaks in between. Considering those peaks, you'd probably want at least 200 K/s to work with. I don't know about you but the Apple Extreme Basestation hardware radios are weak as hell.



    I have a mixed-mode network with WDS repeaters and 200 K/s is tough to maintain on the second hop over WDS.
  • Reply 12 of 25
    Quote:

    Originally posted by Eugene

    Okay, so Apple lossless is anywhere from 75-125 K/s average and that's with lots of peaks in between. Considering those peaks, you'd probably want at least 200 K/s to work with. I don't know about you but the Apple Extreme Basestation hardware radios are weak as hell.



    I have a mixed-mode network with WDS repeaters and 200 K/s is tough to maintain on the second hop over WDS.




    Hi Eugene,



    Well, food for thought on the bandwidth front - however I still don't see what the problem is in pure bandwidth terms. OK so each stream needs 200Kb/s - so what? That still maxes out at just over half a meg in total - I have 11Mb/s (and those with Extreme have 54Mb/s). Seems like plenty of capacity to me.



    Despite being an Apple junkie, I don't use Apple Base station as it never represented value for money to me. I have a netgear ADSL wireless router as basestation. I use the Airport wireless capability within the Macs to connect to the netgear kit. So I can't comment on Apple Extreme base station hardware radios (whatever they are!), and alas I don't know what a mixed-node network with WDS repeaters is either.



    My wifi network is I believe a single hop.



    I can't believe that wireless Ethernet is so limited.



    Neil
  • Reply 13 of 25
    lucylucy Posts: 44member
    Actually that's 200 KB/s as Apple Lossless, like most lossless encoding methods, compresses to about half the size of cda. Which means it is 5 MB/min or around 75-125 KB/s. So this actually does take a fair amount of your bandwidth.
  • Reply 14 of 25
    Quote:

    Originally posted by Lucy

    Actually that's 200 KB/s as Apple Lossless, like most lossless encoding methods, compresses to about half the size of cda. Which means it is 5 MB/min or around 75-125 KB/s. So this actually does take a fair amount of your bandwidth.



    Hi Lucy



    I'm even more confused now! How can 75 - 125kb/s (per stream I assume) represent a fair amount of my available bandwidth? To my (possibly simple) mind I have upwards of 11Mb/s on this wifi network that is not used 99% of the time - if I set up 3 x 125kb/s streams that's still only 375kb/s (though surely it's 128kb/s, not 125kb/s?).



    But hey, what do I know?



    Cheers



    Neil
  • Reply 15 of 25
    pesipesi Posts: 424member
    taking a quick look at bitrates in my iTunes library...



    uncompressed AIFF audio: 1411 kbps (~1.4 mbps)

    apple lossless: 938 kbps (~ .9 mbps)



    where are people getting that airtunes uses apple lossless? that's still a compressed audio format that would require processing in the base station. as well as a recompression on the itunes side. more likely it uses a staright up digital audio stream, which would be the same bitrate (probably plus some) as staright AIFF audio.



    802.11b is NOT 11 mbps. that's peak. real world usage is about 5-6 mbps max. 802.11g is about 23 mbps max, if i recall correctly.



    several streams of even apple lossless would eat up the bandwidth of 802.11b pretty fast, once you figure in packet headers, error correction, etc.
  • Reply 16 of 25
    eugeneeugene Posts: 8,254member
    Quote:

    Originally posted by pesi



    802.11b is NOT 11 mbps. that's peak. real world usage is about 5-6 mbps max. 802.11g is about 23 mbps max, if i recall correctly.




    ~23 mbps max going one way, and even that's only if you're about 10 feet from the access point with LoS. Chop that in half if you're going from one wireless client to another. Add some more distance and the number dips further. Add WDS and it drops again... Mixed-mode? Even less...
  • Reply 17 of 25
    Quote:

    Originally posted by Eugene

    ~23 mbps max going one way, and even that's only if you're about 10 feet from the access point with LoS. Chop that in half if you're going from one wireless client to another. Add some more distance and the number dips further. Add WDS and it drops again... Mixed-mode? Even less...



    If this is the case then my 11mb/s wifi network will barely support Airtunes as it currently is - even though it's limited to just one stream at a time - and 54mb/s will barely support point to multipoint. Sooo what's the solution? better compression? QoS of some sort? Even more bandwidth?
  • Reply 18 of 25
    jherrlingjherrling Posts: 80member
    Ok I have some numbers of my own to throw around.



    802.11g is rated at 54 Megabits per second real world is around 20 Megabits



    so 20 Megabits divided by 8 (8 bits in a byte) will give you around 2.5 Megabytes per second



    Now streaming a 4:02 AAC song at 320 Kbps at 48 kHz sample rate only takes around 40 kilobytes to 50 kilobytes to stream.



    This is far under the 2.5 Megabyte limit so even with AIFF I doubt bandwidth would be a problem for two streams.



    More than likely the problem is the processing power of the APe base station. The computer I have streaming only dedicated about 1% of it's CPU power to iTunes where the receiving end is requiring about 15% (approx 10-12% with same speed chip). so it does require more processing on the receiving end. But they only need to handle one stream so that is not a problem because you would be using two, one on each sound system.



    The computers I used for this test are as follows

    receiver: PowerMac G4 733 Mhz 640 RAM OS X 10.3.3 iTunes 4.5

    broadcaster: Powerbook G4 1 Ghz 256 RAM OS X 10.3.3 iTunes 4.5



    So to make a long story short it should be easily possible and they probably won't include it until an update or something else comes along.



    just my 2¢
  • Reply 19 of 25
    eugeneeugene Posts: 8,254member
    Quote:

    Originally posted by jherrling



    Now streaming a 4:02 AAC song at 320 Kbps at 48 kHz sample rate only takes around 40 kilobytes to 50 kilobytes to stream.




    Except the music is transcoded to a lossless formatwhich averages 2-3x the bitrate and probably peaks at 4x the bitrate. So let's keep it at 200 K/s. Two streams, one wireless client to an AEBS to an AirPort Express remote, obviously doabl in most cases, as it requires about 400 K/s. Multicasting? That requires 600 K/s and the radios will fight each other too. Increased SNR and lower RSSI will result. I average 1.5 M/s from one client to another when I'm in the same room, but even that is subject to lots of sudden drops in throughput that only a massive buffer would solve...
  • Reply 20 of 25
    airslufairsluf Posts: 1,861member
    Kickaha and Amorph couldn't moderate themselves out of a paper bag. Abdicate responsibility and succumb to idiocy. Two years of letting a member make personal attacks against others, then stepping aside when someone won't put up with it. Not only that but go ahead and shut down my posting priviledges but not the one making the attacks. Not even the common decency to abide by their warning (afer three days of absorbing personal attacks with no mods in sight), just shut my posting down and then say it might happen later if a certian line is crossed. Bullshit flag is flying, I won't abide by lying and coddling of liars who go off-site, create accounts differing in a single letter from my handle with the express purpose to decieve and then claim here that I did it. Everyone be warned, kim kap sol is a lying, deceitful poster.



    Now I guess they should have banned me rather than just shut off posting priviledges, because kickaha and Amorph definitely aren't going to like being called to task when they thought they had it all ignored *cough* *cough* I mean under control. Just a couple o' tools.



    Don't worry, as soon as my work resetting my posts is done I'll disappear forever.
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