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Re: LF: VLF vorbis stream, Question

To: [email protected]
Subject: Re: LF: VLF vorbis stream, Question
From: Tobias DG3LV <[email protected]>
Date: Sun, 21 Jun 2015 14:58:12 +0200
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Hi Stefan, LF !

For the suitability of "(ogg) vorbis" format as a transport for antenna (or IF) signals please consider reading the articles at english or german Wikipedia about the technical details of this lossy(!) audio codec :
https://en.wikipedia.org/wiki/Vorbis

https://de.wikipedia.org/wiki/Vorbis

The output of vorbis is completely "synthetic" (as "MP3" is) and targeted to the human ear and brain as a "receiver", but not for an RF receiver and subsequent DigitalSignalProcessing.
But there is a (free, too) alternative : a lossless(!) audio codec "FLAC"
https://en.wikipedia.org/wiki/FLAC

https://de.wikipedia.org/wiki/Free_Lossless_Audio_Codec

Both codecs are implemented in the free "FFmpeg" suite, available for Windows and Linux (Raspi ?) and other OSes.
https://en.wikipedia.org/wiki/FFmpeg

https://en.wikipedia.org/wiki/List_of_hardware_and_software_that_supports_FLAC

73 de dg3lv Tobias

Am 20.06.2015 um 21:04 schrieb DK7FC:
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




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