Stefan,
Referring to my previous posts I'm looking
for a solution of the problem of obtaining
audio at 192kc/24bit and streaming it
via WLAN to elsewhere at very low current
consumption.
I've tested thin clients incl. the M-Audio
192, but >15 Watts of supply power is hard to
provide at remote sites, far from mains, 24/7.
In contrast the R-Pi consumes only 0.5 Amp.
@5 Volts, sound card and WLAN-stick up and
running.
You wrote:
> Raspi, OK, understood.
Fine. No GUI, no mouse, no keyboard, no display.
Only remote access via ssh - and a cup of hot tea.
> Which kind of data do you transfer?
For your convenience I'm using uncompressed
plain audio in Microsoft "riff" aka *.wav.
> A certain RF spectrum?
Yes, VLF/LF, high pass filtered at Wolfson-DSP,
from 5 kc up to the Nyquist frequency at 96 kc.
As I mentioned before there is some breakthrough
folded back from the 2nd Nyquist domain (EFR-tx).
May be a feature?
> What kind is the ADC?
> Are you using a ready to use USB
> soundcard or a single ADC connected to the RPI, via SPI oder so?
Citation Farnell:
"AUDIO CARD, FOR USE WITH RASPBERRY PI". See:
http://www.farnell.com/datasheets/1805130.pdf
There's no USB sound card available which provides
what we are aiming for (on R-Pi).
> Data rate, bits,
"arecord -D hw:0 -r 192000 -c 2 -f S16_LE from_rpi.wav"
This cryptic linux lingo can be translated to:
- read from sound card device "hw:0"
- at 192000 of sample rate,
- 2 channels,
- 16 bits little endian (S32_LE works)
- to a riff-file "from_rpi.wav"
(or pipe it by ssh via network as shown).
> SNR?
Typing "iwconfig" on R-Pi:
wlan0 IEEE 802.11bgn ESSID:"SecretService"
...
Bit Rate=54 Mb/s Tx-Power=20 dBm
...
Link Quality=43/70 Signal level=-67 dBm
...
> Streaming via cable or via a RF link?
Just checked:
R-Pi ==> WLAN ==> router ==> WLAN ==> Linux-box
2 very short glitches over ~1 hour;
may be due to my very old router.
This is only a proof of concept and I don't know how
to stream that huge amount of data reliably over
unstable WLAN-dx-links. May be Paul Nicholson's
"vlfrx-tools" could be a solution.
Laura
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