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Re: [Discuss-gnuradio] Compressing gnuradio data with flac
From: |
mgray |
Subject: |
Re: [Discuss-gnuradio] Compressing gnuradio data with flac |
Date: |
Sat, 5 Feb 2005 13:19:05 -0700 (MST) |
I tried the same program on a multi-carrier NB FM sample set. The flac
compression was worse than bzip2
nws_nbfm_4_stations_256k_complex.dat
uncompressed: 52.8 MB
bzip2: 16.3 MB
flac compressed: 26.4 MB
My guess is the NTSC siganl contained data that appears much like music
data when using its polynomial/LPC routine. So the compression worked
well. Complex (I/Q) multi-carrier NB FM doesn't model so well.
What is interesting is that bzip2 does so well with an IF signal that
should appear mostly as white noise. However, looking further at the raw
I/Q samples, much of the ADC dyanmic range is unused and the upper bits
are 0. With stronger or wider bandwidth (i.e. NTSC), compress will
probably fall off.
Samples at: http://kd7lmo.net/ground_gnuradio_ota.html
Thanks though for pointing out flac. Lossless audio compression is pretty
cool. I tried it on some music .WAV files and it worked well.
On Sat, 5 Feb 2005, James Smith wrote:
> A while back, I downloaded the
> ntsc-short-complex-baseband-8MS.dat.bz2 sample to
> experiment with. Recently, I was wondering if bzip2
> was the best compression to used, so I compressed the
> sample (after bzip2 decompression) with flac. I
> specified a sample rate of 8 Khz since it would not
> accept 8 Mhz. I used the options: "--endian=little
> --channels=2 --bps=16 --sample-rate=8000
> --sign=signed" and left the compression level at the
> default. After decoding the file with the options
> "-endian=little --sign=signed --force-raw-format", I
> ran md5sum and comfirmed that the output was
> identical.
>
> Summary for ntsc-short-complex-baseband-8MS.dat:
> uncompressed: 124 MB
> bzip2 compressed: 66 MB (as downloaded)
> flac compressed: 37 MB
>
>
>
>
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