Natural Science Forum / Physics / Acoustics / April 2006

I was not able to listen, but it is not unusual at all for radio
interference to get into electronics especially if you are anywhere near a
strong transmitter.

S Jones <szg65@yahoo.ca> wrote in news:mID%f.59624$VV4.1101593@ursa-
nb00s0.nbnet.nb.ca:

Make up a dummy mic input connector with both R and L pins shorted to
common/ground and insert it into the mic input on your sound card.  Use
whatever software that came with the card to set "ALL" gains of "ALL"
inputs on the sound to zero. If you still hear voices on playback, you will
need to get another sound card that is better designed in terms of its
susceptibility to radio-frequency interference.  The only other possibility
is that there is that you have a radio-freqeuncy interference problem with
the electronics that you are using to amplify the output of your sound
card.  

    I played 2 4 and 11, and all I heard was solid state noise (static
hiss). No voices, sorry. I have often listened to this sort of
solid-state preamp noise, and sure enough, listen to it long enough and
your mind starts to make out what it would like to hear... faint
"voices" are not unusual in that case.

    Yes, there is a possibility that the electric waves of strong local AM
stations can get into the mic preamp, especially if there is no ic (open
terminal), and you will hear the program material for sure. The front
end solid state circuit will act as a crystal receiver. But when this is
occurring, you usually can modify it by touching a finger to the meter
case, or placing that finger near or on the microphone terminals. And of
course, you might really recognize the program or music content as
coming from that local AM station familiar to you.

    I hear sufficient solid state hiss that whatever stuff you find 10 to
20 dB down from that level will be of no consequence as compared to that
electronic noise.

    I also listtened  to a 'breath out' WAV, and there was less hiss there.
Is it that the 'no-mic' WAV's are with an open mic mount? if so, then
extraneous electrical noise is picked up or generated by the input
circuit, so that the test is unfair. The correct way to do this is to
use a dummy load that equivocates the electric impedance of the
microphone... typically 50 picofarads or so for air condenser microphones.

    Angelo Campanella