"djbrow54" <davebr@...> wrote:
>
> I sort of follow this. Don't these devices phase-lock to the
> frequency of the pilot tone? The AtomPro doesn't have the processing
> capability nor the phase-lock capabilities to do any of this. Even if
> you replace the resonator with an xtal, you still have to synchronize
> them due to power-on and instruction execution differences.
I do understand the limitations of the PSIM's processing capabilities
regarding this syncing situation - I am just trying to sketch for you
the extent that the musical and audio/video industries have gone in
the regard of 'syncronizaton.' It is a rather complex issue to try to
sync up a video tape recorder, running off of a 59.97 khz NTSC pilot
tone, to a digital audio workstation, running at 48 khz, so there
exists "Master Sync Generators" that output a variety of Xtal-locked
sync tones for various formats and media. (Aren't you glad that the
PSIM is not spec'd for audio?!)
As such,
> I think each PSIM needs to be externally synchronized to some type of
> external unit.
>
> What kind of time resolution is required for events? 1 mS, 10 mS?
This is where a decision has to be made - is sync source tempo
related, or is it a very high frequency tone that all time references
are subdivided? MIDI clock is a tempo related time reference -
although it is relatively low resolution, the tempo contiuosly varies,
so at least you have that amount of resolution at all tempos.
>
> There isn't much time available in a 1 mS interrupt routine but there
> might be in a 10 mS interval. That would allow the main code to
> execute and calculate output values, and then an interrupt routine
> could actually do the output. Just setting the four DACs requires
> ~760 uS.
At 120BPMs, a sixteenth note is 125 ms - so 1ms would be acceptable in
a world of interrupts that can keep the errors from accumulating into
larger numbers. 10ms is too large an interval - it would be very
noticeable - like the difference between jazz musicians and classical
players playing a shuffle.
However, if the interrupt latency was the same for each PSIM
> depending upon the code, they would more or less stay in sync but just
> be delayed from the external clock. That might work.
Latency, although annoying can be worked around - I return to my
DAW-synced model - let's try to record a pilot tone into a DAW, and
then play it back to drive the PSIM. If this syncronization scheme is
working, then the PSIM would play back with identical latency on each
pass, and the performances would be identical.
>
> It seems to me that this external unit could translate the pilot
> tone into an appropriate external clock and sync for the PSIMs. P6
> and P7 could be used for external clocks. Both can be setup for
> external edge interrupts so one could be used for a master
> synchronized reset and one could be used for a clock. Or, if latency
> could be tolerated, for serial communication where the data provides
> the intelligence as to clock or reset. Multiple PSIMs could each
> monitor the same master signals.
What you are describing is exactly the setup in Video/Digital Audio -
a pilot tone Master Sync Clock, with Timecode, which each and every
dyncronized device periodically looks at to see if there is any error
to correct, from time to time...
>
> Does such a unit exist? I would think there could be pilot tone
> clocking units. I have no first hand knowledge of any of this.
http://www.soundonsound.com/sos/1997_articles/oct97/aardsync.htmlhttp://www.soundonsound.com/sos/1997_articles/jan97/motumtpav.htmlHere are a few links to a few devices that meet your description.