Over in this thread (http://forums.slimdevices.com/showthread.php?t=93317), there is some interest in a 4- or 6-channel Squeezebox product. So rather than hijacking that thread, I thought I'd try to kick-off a discussion of the possibilites.
I have a pair of home-built transmission line speakers. I put the crossovers in separate modules under the cabinets, so inside the cabinets all I have is speaker cable running directly from the driver units to a 4-way socket on the back.
With all this support around here for active speakers, and now again this discussion of software crossovers, I realised that my speaker build gives me the option to convert them, without touching the cabinets, into active speakers.
I could replace the crossover modules with, say, linked digital plate amps (such as http://www.hypex.nl/index.php?option...d=75&Itemid=91), which allow the crossover settings to be adjusted in their internal software. But I could also 'unlink' those plate amps, flatten the crossover, and feed them with (DSP-processed) signals from synced SBs. I wonder how good the syncing could be made.
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2012-01-30, 05:55 #1
Hardware mods to perfectly sync two (or more) SBs?
Last edited by chill; 2012-01-30 at 06:04.
2012-01-30, 06:04 #2
- Join Date
- Apr 2010
I rasied this question some time ago, and was told that as it stadsn there is no way of syching 2 squeexoes perfectly to get left channel right channel. However I seem to rmember that there is now the facilty to use 2 squeezboxes as the left and right of a stereo pair. thuis must mean they are synched, but seems to assume they are each playing in mono.
But could this be tweaked to allow each of the two sbs to have 2 separate channels.
I have the feeling that as this stadsn its more of a begging letter to logitech than a DIY item, but if anyone is reading it would be great if we could have 4/6 channels via LMS
2012-01-30, 06:13 #3
I've obviously also missed the fact that they can now be synched for left/right - is there some information about that somewhere?
Mono playback would clearly be a requirement in that case. But if they are synched well enough to do left/right, they ought to be able to do bass/treble, didn't they? One SB is EQed to supply the left and right tweeters, the other to supply the bass drivers.
2012-01-30, 06:14 #4
Define "perfect sync"? Are 10ms not good enough? If not, what exactly is it that you need?
I doubt it's a hardware issue, it will be a question of software and turnaround times in the network. Sync works by detecting offsets between the two players and dropping frames to correct that, you need to define an offset you want to detect that is too big so you are willing to accept to drop frames to compensate for the drift.
Also, do I understand correctly that what you want is to have_different_ channels to be sent to the SBs? That would probably require bigger SW changes on the server side, it's - again - completely independent on the hardware.
You can't avoid drift between the different device, no matter how good the hardware, even environmental conditions like temperature play a role, if you really want the HW in sync (that is: with only small drift) you need a completely controlled environment and pretty expensive clocks.
2012-01-30, 06:22 #5
And yes, I appreciate that doing this in software with the current architecture is tricky, probably not practical, but what information would need to be shared, say by a dedicated hardware link between the devices, to slave one from another? The audio is obviously buffered separately, but if it was played out by synched clocks would that solve it - perhaps in combination with the built-in software solution?
So a clock-out/clock-in mod - would that do it? Surely the mechanics of that have already been worked out, for slaving to a DAC.
2012-01-30, 06:28 #6
2012-01-30, 07:18 #7
That doesn't work over a distance.
Sync as it is now allows a drift of 10ms which equates to 3m distance. That's something you can hear in an average room. I don't know, but if you have a good network (not too much latency), high data rates (so that you've got frequent communication between server and client) you might be able to bring it down to 1ms without hardware changes. Is that good enough? Probably if you don't want to pin your head at a fixed point where you want to listen.
2012-01-30, 07:55 #8
- Join Date
- Jul 2009
2012-01-30, 09:58 #9
But that's not the point of the thread. Pippin - are you saying the clock syncing signal can't be carried over a long cable? What if the synced SBs were next to each other, and only their outputs have to travel a distance?
2012-01-30, 14:43 #10
- Join Date
- Jul 2009
In terms of hardware mods, there are a few things I can think of. Using one clock for both units would get them playing at the exact same rate, like you mention, which is a good start. From what I recall there are a couple clocks, both around 24 MHz. Differential line drivers and receivers should be used, and with that you should be able to get a few meters length without problem. Another signal to combine would be the hardware reset. This would get the CPUs started up at the same time, which might help.
However this won't do anything about the players starting their stream at a slightly different time. Ethernet is nondeterministic, and Wifi even more so. I can't think of any hardware that will improve this, but I can think of software solutions, like using a multicast packet to start the stream.