Hi all,
There are vorbis streams available on VLF by Paul Nicholson and
Wolf/DL4YHF and a few more known people from the scene. As far as i
know these are in vorbis format, like my MF/VLF stream.
What i found yesterday, the data rate depends slightly on the volume
level.
Now i'm asking myselfe if there is a 'quality' loss when using a low
mic volume level ??
To become more precise: The usual method is to check where the noise
level of the soundcard can be found, e.g. in Speclab it shows -120 dB
for example. Then, if one connects the RX, it may rise to -118 dB (in
what ever FFT bin width and Mic gain level). Then, connecting the
antenna to the RX may let the (daytime!) noise level rise to -100 dB.
Then one knows that the daytime band noise level is 18 dB above the
noise level of soundcard+RX and everything is fine and
the dynamic range is somewhere near 100 dB or maybe just 90 dB but at
least it is high enough...
Can this method or thinking be applied when SpecLab is getting its
data via a vorbis stream???
I can detect the noise level without an antenna connected and prove
that it is about 20 dB lower as when the antenna is connected. So i
assumed that everything is all right. But when playing with the mic
gain level, i can see that the data rate rises about 10% when adding
another 20 dB. So is there a loss of data, resulting in a lower SNR of
incoming signals when using a low mic level, although it is still well
enough above the soundcard+RX noise?? (Of course i want to keep the mic
level as low as possible without a quality loss, to have a dynamic
range as high as possible)
I just noticed that effect last night and now i'm aksing if there are
unwanted losses.
73, Stefan
|
|
