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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


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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