At 11:47 AM 3/7/2007, you wrote:
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>Friends:
>
>I often use a single microphone (in a parabola) with a minidisk recorder
>that only records in stereo --- so one track is "wasted". Plus, the
>recorder doesn't allow independent adjustment of the record levels for
>the two tracks.
>
>I'd like to split the signal from the microphone into two wires, put
>something like 20dB attenuation on one of them, and then combine these
>two back into two channels of a single stereo input for the MD recorder.
>The goal is to provide myself with some protection from setting the
>record level too high. The intended effect is roughly what I'd get if I
>set the record levels differently for the two channels.
>
>Can anyone suggest easy to find parts that'll let me do this? I imagine
>it is something everybody's already doing and that I'm just slow with
>getting to the idea. Or maybe its a bad idea for some reason?
>
>So far, I have a connector that adapts the microphone and converts to a
>stereo mini plug with the signal on one of the channels (the tip, I
>believe) and I imagine there should be bits of wire and connectors
>that'll get me where I need to be. How do I supply the attenuation? Can
>I make it adjustable in a couple levels?
>
>Thank you for any and all suggestions.
>
>Steve P
Steve: that is a good idea. Wish I'd done it for all my recording trips
while I could still HEAR.
I would suggest letting the mic line go directly to the left (center of
plug?) channel, for noise and reliability reasons. Then get a fixed
resistor, say 5 k (or RTMA 4.7 k is fine) ohms, from the mic line to the
right channel connector on the miniplug, then connect that same point
through a variable resistor of, say 2 k ohms to the common ground. When the=
variable (volume control) is full up to 2 k, the voltage delivered to the
right channel will always be 2/7 the voltage the left channel is getting.
That would be a full open attenuation of 20 x log {0.28} =3D ~ 11 db. As yo=
u
turn the variable resistor down the attenuation becomes more and more,
finally resulting in zero signal into the right channel.
The exact values of the resistors, called a voltage divider, and not that
important but should be in this ballpark. For example a 3 k and a 1 k
would work fine.
Because miniplug female jacks are so notoriously unreliable in the field,
in general, I would mount all this in a very small box, with a stereo
miniplug on a few inches of cable emerging from the box. In practice, plug=
the mic into this box and the box cable into your MD mic port and your are=
off an running.
All my best.
-- best regards, Marty Michener
MIST Software Assoc. Inc., P. O. Box 269, Hollis, NH 03049
http://www.enjoybirds.com/
If you think plants are not important for living, try it without oxygen for=
a few hours.
"I am strongly induced to believe that as in music, the person who
understands every note, if
he also possesses a proper taste, more thoroughly enjoy the whole, so he
who examines each
part of a fine view, may also thoroughly comprehend the full and combined
effect.
Hence, a traveler should be a botanist, for in all views plants form the
chief embellishment."
Charles Darwin, The Voyage of the Beagle
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