Problems connecting wavfile_source to usrp_sink

Greetings, I’m new to the list, though I’ve been using gnuradio for
about 6
months now. I’m using the USRP connected to an acoustic transceiver for
underwater communications/data collection.

I’m having some trouble sending data from a file, specifically a
wavfile_source, to a usrp_sink_c. The block diagram is as follows:
gr.wavfile_source ->blks2.rational_resampler_fff -> gr.float_to_complex
->usrp.sink_c. It doesn’t give me any errors (other than a few "uU"s)
but I
get garbage on the other end of the transmission.

I’ve tested out most of these parts individually, and they work fine.
The
usrp_sink works fine when I use the signal generator. I can read the
wavfile_source, resample it, and pipe it to an audio_sink or a
wavfile_sink
and it does the resampling properly. Assuming I’ve done everything
correctly, am I missing something? Is there some fundamental reason why
one
would be unable to read a file & send it via the usrp? I’ve gotten the
reverse (usrp_source -> wavfile_sink) to work just fine.

Any help would be appreciated.

Justin

P.S. I’ve tried both wavfile_source & file_source & neither work. I’m
aware
of the -1.0 to 1.0 normalization in wavfile_* & have commented that
portion
of the code out. If I get this to work, I’ll write a wavfile_source &
sink
that do no rescaling & take shorts because I’m doing too many unecessary
conversions.

On Wed, May 13, 2009 at 04:25:39PM -0400, Justin G. Eskesen wrote:

P.S. I’ve tried both wavfile_source & file_source & neither work. I’m aware of
the -1.0 to 1.0 normalization in wavfile_* & have commented that portion of the
code out. If I get this to work, I’ll write a wavfile_source & sink that do no
rescaling & take shorts because I’m doing too many unecessary conversions.

For the start, it probably would have been better to put in a
gr.multiply_const_ff() after the filter with a value of something like
20000. In the setup you mentioned, reading shorts from the WAV file
would not have helped, since you’re using a float FIR afterwards, and a
short FIR would introduce too much quantization noise.

I’ve tried pretty much exactly the same setup before (but with the
multiplier) and it worked. Also, for debugging, I recommend using a
file_sink (not a wavfile_sink) instead of the USRP and check the sample
values in that file scale well in the DAC range. Actually, if you /did/
pipe it to WAV or audio, it should /not/ work, since they rely on data
being between -1 and 1.

Should you do ever do write a short wavfile_* and also want to support 8
Bit, remember that scales differently.

Hope this was what you wanted.
MB

Thank you Martin.

Knowing that there is no fundamental reason that this setup would not
work,
led me to investigate a different section of my code & I discovered that
I
was running with a usrp decimation too low for my system & a wav file
with
too high a sample rate.

As for the short int wav file, I’m writing this code so that a number of
students, who don’t use anything but matlab, will have access to the
usrp
board for their various experiments. I can cut out the FIR filter if I
desire & require a compatible input wav file sampling rate… I was just
trying to make it flexible to input wav files of varying sample rates.
I
have a competing desire to make it efficient, as I my be running this on
a
333 mHz PC-104 board. So, its a tradeoff.

That said, it works beautifully now. Thanks again.

Justin

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