Re: [Discuss-gnuradio] Demo Audio Code

[Joseph DiVerdi]

At 11:48 PM -0800 3/4/03, Matthew Ettus wrote:
>I have checked in working GrAudioSource and GrAudioSink files.  They now handle
>1 or 2 streams each.  OSS sound drivers split multichannel cards into separate
>stereo devices, so this doesn't stop you from working with >2 channels.  You'll
>just need multiple GrAudioXXX blocks.
>
>ALSA handles multichannel cards much better, so it will need to be integrated 
>in
>order to do this right.
>
>The source and sink now also handle scaling for you, and both work with
>VrComplex data.
>
>There is demo code --
>    See full_duplex_audio_demo.cc in the src/gnu/examples directory for an
>example of single channel, 16-bit data I/O, full_duplex.
>    See complex_audio_fft.cc in the same directory for an example of Complex
>I/O, also full duplex.  This one will do a complex FFT on the stereo input,
>assuming the Left channel is real, and the right channel is imaginary.  Joesph
>-- this is the one I promised you.
>
>Let me know if you have trouble
>
>Matt

Thanks Matt (et. al.), for your work on this. I'll hunker down and start 
working on this demo code, boning up on C++, clearing the snow off the antenna, 
etc. ;)

FYI, I have managed to capture some actual VLF data using "record" to suck it 
from the sound card and by processing it manually. WWVB (60kHz, Fort Collins, 
CO) shows up prominently while a number of other stations (21.4kHz, NPM, 
Lualualei, HI; 24.0kHz, NAA, Cutter, ME; 24.7kHz, NLK, Jim Creek, WA; 25.2kHz, 
NML, LaMoure, ND; 40.7kHz, NAU, Aguada, PR) have been identified and a number 
of others remain unidentified. WWVB uses ASK (Amplitude Shift Keying) to encode 
time-of-day information while many of the others use MSK (Minimum Shift Keying 
- a form of Gaussian filtered Frequency Shift Keying). I've put up a few images 
of this preliminary acquired data on my web site and am writing up some of the 
technical details (as promised) similarly.

http://xtrystems.com/vlf/images/wwvb_time_1 - one channel of time domain data 
dominated by WWVB
http://xtrystems.com/vlf/images/wwvb_time_2 - one channel of time domain data 
dominated by WWVB
http://xtrystems.com/vlf/images/wwvb_time_3 - one channel of time domain data 
dominated by WWVB

http://xtrystems.com/vlf/images/wwvb_spectrum - detail of WWVB in frequency 
domain

http://xtrystems.com/vlf/images/spectrum_full_30khz - full frequency spectrum 
+/-24kHz centered at 30kHz
http://xtrystems.com/vlf/images/spectrum_full_50khz - full frequency spectrum 
+/-24kHz centered at 50kHz

http://xtrystems.com/vlf/images/spectrum_detail_21.4khz - detail of NPM in 
frequency domain
http://xtrystems.com/vlf/images/spectrum_detail_24.5khz - detail of NAA, NLK, 
NML in frequency domain
http://xtrystems.com/vlf/images/spectrum_detail_40.7khz - detail of NAU in 
frequency domain

http://xtrystems.com/vlf/images/wwvb_xy - WWVB real and imaginary channels 
plotted against each other (my personal favorite)

Best regards,
Joseph

-- 
Joseph A. DiVerdi, Ph.D., M.B.A.          
http://diverditech.com/           970.980.5868 (voice) 
http://xtrsystems.com/            970.224.3723 (fax)
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