[LAU] XLR mixer -> TRS audio card connections

Brent Busby brent at keycorner.org
Sat Aug 15 15:04:22 EDT 2009

Is it wrong to use a regular cable (no transformer) to connect the XLR 
main and submix group outputs of a console to the TRS (balanced) inputs 
of an audio card, or should impedance matching be done in that case? 
It is quite common in music stores these days to find cables that are 
XLR male on one end and TRS male on the other.  (I'm currently using 
those on my mixer outputs.)  The cables *are* balanced, but they do not 
contain a transformer at all.

The impedance of my console's main/submix outputs is rated as less than 
75 ohms, but the input impedance of my audio card is 10k ohm.  This 
would seem to almost answer the question by itself, it weren't for the 
near impossibility of actually finding a matching transformer that's TRS 
and not TS on its 1/4" end.  I looked at a lot of them.  They're all 
made for hooking up guitars, amps, and mics, and they all seem to have 
an unbalanced plug opposite from the XLR end.

If there is indeed a need transformers on each XLR mixer output in this 
instance, where can I get one that won't unbalance the connection in the 
process?  Or is it fine to just use these common XLR->TRS cables that 
don't have any?  The reason I started to investigate this is because I'm 
not sure I'm not getting some of the "tone suck" you might associate 
with a badly matched connection, and this seems a likely cause.

Addendum:  On the realtime end of things, I'm now achievable a solid, 
unbreakable 2ms.  I can't seem to do anything that causes an xrun. 
That's good at least!

+ Brent A. Busby	 + "We've all heard that a million monkeys
+ UNIX Systems Admin	 +  banging on a million typewriters will
+ University of Chicago	 +  eventually reproduce the entire works of
+ Physical Sciences Div. +  Shakespeare.  Now, thanks to the Internet,
+ James Franck Institute +  we know this is not true." -Robert Wilensky

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