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TOPIC: Synchronizing two boxes

Synchronizing two boxes 6 years 5 months ago #12148

  • bobkatz
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I would like to use one OpenDRC for left channel/right channel mains and one for left sub/right sub. I am willing to go inside and make modifications to ensure they boot at the same time and/or are reasonably synchronized.

If I lock the reset pins of one to the other do you think the software of the two boxes would then be in sync? If I lock the output clocks of the two ASRCs together (putting one in master and one in slave mode) do you think even the sample phase differences between the two would be in sync? This would probably not be an audible problem, but an interesting idea for us geeks who think we can hear a pin drop in the next room ;-).
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Synchronizing two boxes 6 years 5 months ago #12186

  • bobkatz
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Bump... No one seems ready to tackle this question??? Thanks for any help. Bob
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Synchronizing two boxes 6 years 5 months ago #12189

  • curryman
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Why would you want them to finish booting the same time? Whether the subs start to play music some ms earlier or later shouldn't be a problem :unsure:

To synchronize the clocks could be of more interest, however currently there is no I2S slave firmware available. When a slave option will be available it could be done. Not sure if it will be really audible as you already mention though ;) Different MCLK frequency would lead to a change in audio frequencies (e.g. 1kHz sine beeing 1.001kHz) in this case :unsure: How much could this be with e.g. a 50ppm XO?

Good to have you here Bob :)

regards, Daniel
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Synchronizing two boxes 6 years 5 months ago #12190

  • bobkatz
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curryman wrote:
Why would you want them to finish booting the same time? Whether the subs start to play music some ms earlier or later shouldn't be a problem :unsure:

Thanks for replying to me, Daniel. It's good to have you here. Well, I'm worried that on different boots, the latency of the processing of the subs will be different than the latency of the satellites. As far as the reset pulse, I am under the impression that the ASRC chip which is being used boots up with different latencies. I would like a hardware designer to confirm or deny that, please. Typically, on power up, the system has an RC delay circuit which waits till there is power and then it pops the reset line of the processor and/or the ASRC chip. If this action is not synchronized, I'd like to know if it could result in different delay. I'll experiment with that after I get my boxes, which I have just ordered at the Mini-DSP store.

To synchronize the clocks could be of more interest, however currently there is no I2S slave firmware available.

Assuming that synchronizing the clocks is important or necessary. If so, I don't have to wait for a firmware change, I can cut some traces and change one chip from master to slave mode and feed the clock line from one box to the other directly if I wish. I can't tell you how many boxes I've built and modified over the years and as long as I can psyche the schematic I can do this :-)

This kind of clock synchronization is totally important for digital mixing, but if the timing is still within a few samples, it shouldn't affect the perceived latency of the subs at all. That's what I need to find out. You'll be sure to hear about it. I can't believe I'm breaking new ground in the Mini-DSP world by trying to run two Sharcs in parallel in one audio system!
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Synchronizing two boxes 6 years 5 months ago #12192

  • dreite
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You're a ground breaker Bob. :) The vast majority of us are domestic users and only have one miniSHARC board. Wouldn't even have considered using two....and if using two wouldn't have worried about syncing them. :)

Will be interested to follow your progress on this.

Dave.
Last Edit: 6 years 5 months ago by dreite.
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Synchronizing two boxes 6 years 5 months ago #12219

  • curryman
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bobkatz wrote:
Well, I'm worried that on different boots, the latency of the processing of the subs will be different than the latency of the satellites. As far as the reset pulse, I am under the impression that the ASRC chip which is being used boots up with different latencies. I would like a hardware designer to confirm or deny that, please. Typically, on power up, the system has an RC delay circuit which waits till there is power and then it pops the reset line of the processor and/or the ASRC chip. If this action is not synchronized, I'd like to know if it could result in different delay. I'll experiment with that after I get my boxes, which I have just ordered at the Mini-DSP store.

AFAIK the delay/latency of the ASRC (SRC4382 from TI) depends on the used interpolation and decimation FIR filters and the FIFO Buffer size. The FIR fIlter length depend on the input to output sample rate ratio which would be the same for both openDRC in your setup I guess. Also the FIFO Buffer size should be identical (if changed from default = 64 samples at all).
I did some measurements with the miniSHARC + DIGI-FP using my RME DIGI96 with synchronized digital I/O and can not remember that I encountered a varying latency after several restarts, however this was not my focus.
bobkatz wrote:
Assuming that synchronizing the clocks is important or necessary. If so, I don't have to wait for a firmware change, I can cut some traces and change one chip from master to slave mode and feed the clock line from one box to the other directly if I wish. I can't tell you how many boxes I've built and modified over the years and as long as I can psyche the schematic I can do this :-)

I'd be interested to see how you do this (changing I2S master/slave behaviour) :huh: Feeding the same clock to both boards should indeed be generally possible with some hardware hacking (warranty). I think I will wait for the master/slave firmware :whistle:

kind regards, Daniel
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Synchronizing two boxes 6 years 5 months ago #12223

  • John Ashman
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It would be SO nice at this point to have an OpenDRC with 8 analog balanced/single=ended outputs, both stereo digital and analog inputs. Problem solved.

Also, Mr Katz, have you considered going to three and using the OpenDRC for high slope digital crossover between the tweeter and midrange? Nothing better for nearfield listening, except a 96dB crossover, perhaps.....
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Synchronizing two boxes 6 years 5 months ago #12251

  • zydeco
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I'm also interested in this topic. Agree that it'd be great to have a true multi-channel OpenDRC solution (ideally with both digital and analog inputs). It'd be good in the interim, however, to understand how to use multiple miniSharc or OpenDRC to meet this goal.
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Synchronizing two boxes 6 years 5 months ago #12286

  • Draki
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Hi
I am in no way expert, but it just happened that I communicated with Uli on a similar subject (actually I was asking, he was responding and advising....).
I am quoting from one of his answers (moderator: I hope this OK, if not please edit as appropriate) : " Because of the limited filter length by the OpenDRC AcourateDRC generates only filters with amplitude correction.
This means: easy use but restriction with filter quality ".

If you are building the backup system based on openDRC, you could use the amplitude-only corrections, not phase/time etc.
So it will not be 100% same as the main system.

Sorry if offtopic, thought might chime in.

Rgds, Draki
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