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Itech digital input active thru


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#1 Nicolas Lowman

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Posted 09 November 2005 - 10:22 PM

Monday the boss and I started working on using the digital inputs into the Itechs. Here is the problem that we encountered. When coming out of the DBX Quantum processor via the digital output going into the digital in on the Itech the first amp in the chain received signal. However the signal was not passed on to the other amps in the rack via the active digital out. This is what happened with the DBX at 96K. We checked cables and several other things without any luck. Finally we switched the clock on the DBX to 48K and the Itech passed signal onto the other amps.

Is the amp always going to be able to pass only 48k and below or are there plans to upgrade this?
Or is there something I am doing wrong.
Thanks,

Nicolas Lowman

#2 DGlass

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Posted 11 November 2005 - 09:45 AM

Even in a small AES/EBU system AES/EBU is not a simple standard to implement. Things such as if the cables are true 100-ohm XLR or 74-ohm BNC AES/EBU cables, distance of the cables and quality of the cables can make a major difference on if the digital clock and data signals get from one place to another and are usable.
What appears to be happening is the leading edge of the clock signal is being skewed. The clock signal is probably just readable by the first amp. Due to the clock speed when the signal is passed on to the next amp the clock signal has been skewed enough to cause the digital input of the following amp(s) to not be able to sync to it. When switching to the 48 kHz lower clock speed the skewing of the signal is not as pronounced and the other devices have time to sync onto the signal.

This is a know issue with using AES/EBU or any digital audio signal if the clock signal has become degraded. This can however be overcome, to some extent, by re-clocking the signal with a device such as a DDA (Digital Distribution Amp) like that made by ATI. http://www.atiguys.com/   or    http://www.atiguys.com/?fa=search&text=DDA  
By re-clocking the signal you will be able to pick up from several to many more AES/EBU devices, at the higher 96kHz clock speed, depending on cable and signal quality.