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Author
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Topic: External 6-channel interfacing of two sources
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Joel N. Weber II
Expert Film Handler
![](http://www.film-tech.com/ubbmembers/3530a.jpg)
Posts: 115
From: Somerville, MA, USA
Registered: Dec 2005
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posted 01-27-2007 01:49 AM
quote: Frank Angel You might also look into one of those KVM swithches (for switching computer keyboard, monitor and mouse between two or more computers). There should be more than enough conductors for + - and Shield for your application. You would just have to make the break-out cables, which is easy enough. Only thing you would have to check is if the isolation circuit in a KVM switch will impact the audio signal. I seem to remember the last time I opened one of those boxes up, I did see few diodes and resistors, but I believe those were just used to block any DC and to make sure there was no crosstalk between connections. If that doesn't impact the audio signal, these would be nice in that it would be a single switch instead of two for a projectionist to have to deal with. The couple we use have mechanical indication push buttons as well, i.e., a little bright thing flips up in the button to show which is active....nice.
Analog video cards typically have 8 bit DACs. The keyboard and mouse signals are purely digital.
Whereas good digital audio is typically at least 16 bits.
So the tolerable noise floor for video is probably substantially higher than for high quality audio.
The frequencies used might also be an issue. A single cycle of a sine wave going to a subwoofer can take longer than 1/60th of a second, whereas the less frequently updated monitors typically have hundreds of thousands of pixels redrawn in the space of 1/60th of a second.
When you ``block DC'', you are actually picking some appropriate cutoff frequency, and even if you're just repurposing a PA microphone mixer to mix subwoofer signals, I think you might need to watch out for what the cutoff frequency on the DC blocking is.
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