Reply To: QU Pack as an audiorack?

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Andreas
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…trying to describe the problem from the system side. In a digital audio world any processing is performed on samples, some so called discrete representation of an otherwise continuous audio signal. On a Qu system there are about(!) 48.000 samples processed per second, other systems may use 44.100 or even 96.000 samples per second, just to name some numbers.
This samplingrate is derived from some electrical oscillator somewhere in the MHz range, crystal oscillators are pretty common here, since they provide a somewhat precise reference frequency.
Sadly any such oscillator has some more or less good precision measured in ppm, 20-50ppm is a common value (additionally depending on board layout, temperature, humidity etc.). 50ppm means, the resulting samplingrate is somewhere between 48.002 Hz (48.000 * 1.000050) and 49.997 Hz (48.000 * 0.999950).
If two devices derive their samplingrate from separate oscillators and try to exchange samples digitally, you may get an excess (overflow) or shortage (underflow) of up to four samples per second.
For this reason any component within a digitally interconnected system needs to be properly synchronized in terms of samples, that’s what a central wordclock is used in a digital studio. There is exactly one master providing a hopefully stable and jitter-less clock reference in such an installation.
The Qu does not have a wordclock input and only serves as a clock master, the AR/AB stageboxes, in contrast, are slaves and synchronize to the Qu(/GLD) via the dSnake. These stageboxes do not necessarily need an internal stable clock reference for audio, since they’re not intended to run standalone.
And so we finally come back to the Qu-Pac, wich essentially contains the Qu32 engine (more or less knobs does not matter regarding system design). To make the Qu-Pac a stagebox for a Qu16/24/32, it needs to be able to synchronize itself to the master console on the other end of the dSnake which requires some smart internal clock circuit (hardware) able to switch between a fixed crystal (for standalone mode) and some synchronizable VCO/PLL/VCXO or similar.
This is no rocket science, A&H already have something like this in their stageboxes, but I really doubt this is part of the Qu design (it would have a word clock input if it could syncronize to other gear).