xy at wrote on 7/2/04 12:47 PM:

Analogue line inputs-6

....
Stereo Crosstalk (1kHz at -1dBFS): -115dB
THis means that a 1kHz tone blasting at essentially full level on ONE
channel (with NOTHING suppsedly on the other channel) will leak across to
the other channel at -80dB
This spec is limited as defined (only at 1kHz... you want to see this rated
at full bandwidth 20-20kHz or at least in the upper end where it's really
noticed.


Common-Mode Rejection (60Hz): 40dB
this tells how well-matched each leg of a ballanced line is.
the LARGER the figure-- the GREATER the common noise rejection (induced hum
on a mic cable or such, hence the rating at 60Hz)
Theoretically ANY signal coming down EACH of the signal legs (pin 2 and 3)
with the EXACT SAME LEVEL and polarity will completely cancel out at the
signal input. Transformers do this inherently. electronically balanced
inputs are less precise, so Real Inputs on Real Gear include a trimmer on
one or both legs so this can be precision matched... haven;t seen THAT on
anything in the affordable vein recently.

--
John I-22
(that's 'I' for Initial...)
Recognising what's NOT worth your time, THAT'S the key.
--

xy wrote:

what's the difference?

i'm looking at specs for the new Emu 1820m.

below are the specs. the common mode rejection always seems to be
many db less than the crosstalk db. i don't think i understand
"common mode rejection".

Common mode rejection is the ability to purposefully combine signals
from two adjacent wires (on a balanced input) to avoid picking up the
noise that they both experience equally along the way.

Crosstalk is when you *accidentally* combine the signals from two
nearby wires (through some kind of coupling) and so each wire's signal
becomes noise on the other wire. Channel separation is the extent
to which you manage to avoid crosstalk.

So basically crosstalk is "hey, you got your peanut butter in my
chocolate" and common mode rejection is "hey, your peanut butter
and my peanut butter were opposite polarities, and they both
got equal amounts of chocolate in them, and now by subtracting
your peanut butter from mine, we have eliminated the unwanted
chocolate."

- Logan