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View Full Version : Synchronized Squeezeboxes



shawkie
2006-04-26, 06:22
As I understand it, when you synchronize multiple Squeezeboxes they re-sync at the start of each track. Apparently this stops the gapless playback (of lossless formats) from working.

How quickly do the Squeezeboxes drift out of sync? Is this caused solely by differences in the DAC clock frequency?

Is it really necessary to re-sync on every track?

What happens if the Squeezeboxes are playing an internet radio stream? Do they ever re-sync?

Is it possible for two Squeezeboxes to drift massively out of sync (e.g. >10 sec) over prolonged periods (e.g. >1 day) when playing internet radio streams? Does it eventually reach a point where the faster Squeezebox runs out of data and the slower one overflows a buffer? What exactly does happen?

Surely this same problem is seen in DAB radio and DVB television and all sorts of other places. How is it normally handled?

krosfyah
2006-04-26, 09:08
I have two SBs that I leave synced. If I hit pause and come back the next day or two, sometimes I see a <1/2sec delay on one of them. If I leave it run, I don't recall that they get back in sync on the next song. If hit RW or FF, the SBs then get synced up. That suggests to me they are not automatically synced at the start of each song but rather resynced when you manually start a song.

I have never done Internet radio so I can't tell you. I'll go try it out, however, and let you know.

TorbenGB
2006-05-06, 08:36
"What happens if the Squeezeboxes are playing an internet radio stream? Do they ever re-sync?"

Each Squeezebox can *either* connect to the SlimServer *or* to the SqueezeNetwork for internet radio. Players that are connected to the slimserver can be syncronized, but players that are on squeezenetwork can't.

You can also have a web radio in your favorites (in the slimserver), and if you play that, then all players that are on the slimserver and set as syncronized will also play that.

Hope this helps.

thespaugh
2006-05-20, 13:52
Regarding Internet Radio:

It's my understanding that drift between synchronized SBs is inherent given the devices’ buffers. This is the case regardless how you connect (via SlimServer or SqueezeNetwork) to Internet radio stations. SBs sync at the beginning of a track but since Internet radio stations are broadcasting as continuous streams the SBs are not re-synchronized when a track/song changes. Over time you begin to notice the drift. It seems like there is about a .5sec difference between my SBs after 3-4 hours of listing to one radio station (continuous stream). However, it becomes annoying about an hour before that. If you hit “skip,” or change the station the SBs will re-sync again but I don’t find think this is a satisfactory solution.

I have voted for a bug fix which I believe addresses this issue. It’s the “fine-grained network clock” bug.
http://bugs.slimdevices.com/show_bug.cgi?id=259

This bug has been open since 2004 and I’m starting to wonder if Slim Devices has any idea how to fix this…

Perhaps someone for Slim Devices could provide me/us with an update?

Server: SlimServer 6.3 on W2K
Players: SB2 & Two SB3

shawkie
2006-05-26, 06:38
I have seen the bug report regarding this but I wanted to try to understand exactly what the problem was before voting for or suggesting a solution. I am considering buying a second Squeezebox but before I do that I need synchronization when playing internet radio and gapless mix albums.

To be honest, I'm more concerned about gapless mix albums than internet radio. What I don't understand is, if the Squeezebox plays samples at a rate given only by the frequency of the DAC clock then what happens if this is faster than the internet radio station is running? Or is internet radio not actually a broadcast technology at all? Presumably an internet radio station can't cope with 1000s of clients all asking for different parts of the stream? Unless there is some limit on how far the clients can drift out of sync? And what if the internet radio station is actually sampling an audio source in real time? Or maybe the clients are required to buffer say 30secs worth before playing and just hope they aren't tuned in long enough to exhaust this buffer?

What I can't see at the moment is how on earth you can keep two Squeezeboxes perfectly synchronized indefinitely either dropping samples, duplicating samples or adjusting the DAC clock (which would introduce jitter presumably).

radish
2006-05-26, 07:08
To be honest, I'm more concerned about gapless mix albums than internet radio
Me too, which is why I essentially never sync my 3 players. A shame, but gaps are a bigger shame.


Or maybe the clients are required to buffer say 30secs worth before playing and just hope they aren't tuned in long enough to exhaust this buffer?

Bingo. Or rather no client is _required_ to buffer anything but a non-buffering client really isn't going to work very well. Ever seen "Buffering..." when playing back a streaming video or something? Exactly the same thing - rate of consumption exceeds rate of delivery for long enough to exhaust the buffer.



What I can't see at the moment is how on earth you can keep two Squeezeboxes perfectly synchronized indefinitely either dropping samples, duplicating samples or adjusting the DAC clock (which would introduce jitter presumably).

The general idea is, I believe, to introduce checkpoints every x seconds where the players compare where they are in the playback. Then the playback rate (i.e. DAC clock) is adjusted slightly on n-1 players to bring them back into sync. So yes, you'd be adjusting the clock - I can't see any other way of doing it either. I don't think that counts as jitter though - which is typically defined as variations from the ideal clock on a per-cycle basis rather than general deviations in clock rate. I'm sure it'll upset some audiophiles though :)

TiredLegs
2006-07-03, 13:18
Anybody know if synchronization issues with multiple Squeezeboxes are any different with wired vs. wireless networks?

aubuti
2006-07-03, 15:30
I think it's safe to say that some of the issues are the same, but that wireless brings in an additional set of issues that wired doesn't have. The wireless-specific issues are things like one of the SB getting a weak signal (so it can't keep it's buffer full), or the stream to the wireless getting interrupted by a cordless phone/microwave/neighbor's wireless. And of course, that can mess up your sync'ing even if only one of the SBs is wireless and the rest are wired. The issues that are common include the kind of things discussed already in this thread.