Howard White writes:
> BTW... External USB Sound Card Devices such as Rig Expert
> work substantially better (10db or so) than internal sound
> card on digital signals..
This is demonstrably false. The claimed "advantage" comes from
flawed tests which fail to properly set the input level to each
sound device to take maximum advantage of its dynamic range.
Except for the very worst sound cards or exceptionally noisy
systems, internal sound cards have at least 60 dB of usable
dynamic range (the better 16 bit cards have 80 dB of dynamic
range and 24 bit cards with high level inputs can have dynamic
ranges that approach 100 dB). If the audio from the transceiver
is such that the receiver noise floor (no antenna) is six to ten
dB above the noise floor of the sound card, the software DSP
(RTTYrite, MMTTY, etc.) will be able to operate at its full
capacity. Receiver AGC, etc. will limit the receiver output
to a level well below the input capacity of the soundcard.
Most receivers will not vary more than 30 to 40 dB from quiet
band to S9 +40 dB receive signals.
Soundcard performance is not a matter of internal vs. external.
It is a matter of careful attention to setting the proper level
to allow the soundcard to function properly.
73,
... Joe Subich, W4TV
microHAM America
http://www.microHAM-USA.com
http://groups.yahoo.com/group/microHAM
support@microham.com
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