This is only slightly off-topic, as it is part of my project developing
custom control software for my Pegasus.
As part of my Pegasus software project, I am working on developing a digital
voice keyer. To this end, I am recording .WAV files of the letters, digits
and phonetic alphabet. I am trying to do this using a computer sound card
with the Sound Recorder accessory that comes with Windows.
I connected my Heil Gold-Line microphone to my ham shack computer (a 533 MHz
Celeron with soundcard built into the motherboard). The recorded audio
sounds great except that there is a very noticeable whine on the recorded
signal. I processed the signal through the FFT in Gram. There were very
strong narrow frequency lines on the plot at (approx) 1013, 2003, 2994,
3984, 5018, 6108, 6999 and 7989 Hz.(note the spacing is almost 990 Hz in
almost every step, but one). I also monitored the input using DigiPan's
waterfall. In addition to the lines above, there were also fainter lines
approximately every 200 Hz. In normal operation, using the Pegasus line out
to the soundcard line input, these lines are not noticeable.
The whine goes away if I disconnect the cable from the mic input, or if I
disconnect the mic from the other end of the cable. I would have thought
that if the cable (6 feet or so) was acting as an antenna, the whine would
be present even in the mic were disconnected.
I tried using the Gold-Line with my other computer with a soundcard. The
whine is gone, but that soundcard doesn't seem to have enough gain for the
mic. I get a lot of hiss and a low volume recording. I have tried other
microphones, specifically designed for computer soundcards with both
computers. On the hamshack computer, they still produce the whine, but on
the other computer they work fine, other than the audio is not the quality
of the Gold-Line.
I suspect that the problem is in the input circuitry of my soundcard, but I
was wondering if the above suggests any fix (short of disabling the
soundcard and adding a new one).
73,
Mark, N8ME
--
FAQ on WWW: http://www.contesting.com/FAQ/tentec
Submissions: tentec@contesting.com
Administrative requests: tentec-REQUEST@contesting.com
Problems: owner-tentec@contesting.com
|