One solution I use for really noise free audio is posted at:
http://www.geraldj.networkiowa.com/papers/speakerfilter.pdf This filter
has selectable cut off frequencies and being passive and built for
speaker impedance there is no high frequency noise introduced after it
by 100 KHz bandwidth audio output ICs.
73, Jerry, K0CQ
On 8/12/2010 2:46 PM, Stuart Rohre wrote:
Joe,
You may want to read Rob Sherwood's web site on receiver and rig
testing, about excess audio response. He reports operators get tired
listening to any audio above the voice or SSB, needed frequencies.
In fact, you may want to put a band limiting filter in front of any hi
fi headphones to avoid operator fatigue if you do much DX operating.
That has also been our finding at the Acoustics research lab where I
work for the Navy sonar folks. Sonar operators need to only have the
sonar frequency audible components and not a full span of ocean noise.
73,
Stuart Rohre
K5KVH
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