[linux-audio-user] format conversion question (long)

[ben-extra at MIT.EDU]

Hi,

I have a few questions about audio format conversion.  After reading a
description of the purpose of this list, and reading the list itself for
about 10 days, I think this is an acceptable place to be asking.  If, in
fact, my questions are best asked someplace else, please let me know,
and my apologies.

I have quite a few recordings that were made from a RealPlayer 8 live
stream.  As saved by vsound (.au format), they are about 500 Megabytes
each!  Seeing as RealPlayer reports the (original) stream/broadcast as
12.4 Kbps, and the recordings are about 3.5 hours long, I am quite sure
they are being saved to disk with much higher quality then needed.  :-)

My basic need is to reduce their size.  I am not an expert in audio
processing, and I would prefer not to become an expert in order to make
the correct choices for this conversion.  Hence, I hope that this is an
easy question for somebody(s) reading this list to answer.  I don't need
to conserve every possible megabyte of disk space, indeed I would prefer
to be conservative, and not lose any quality.  The recording is of low
AM radio quality as it is...

I have sox installed on my system, so I am trying to use that.  I read
through the man page.  I don't feel a need to have stereo, so I took a
wild guess as to what rate would be appropriate and did the following.
My attempt was to produce a mono recording at 8000 samples per second.

marit at chipmunk:/var/tmp$ sox -V test.au -c 1 -r 8000 test.wav polyphase
sox: Detected file format type: au

sox: Found Sun/NeXT magic word
sox: Input file test.au: using sample rate 11025
        size shorts, encoding signed (2's complement), 2 channels
sox: Input file test.au: comment "test.au"

sox: Writing Wave file: Microsoft PCM format, 1 channel, 8000 samp/sec
sox:         16000 byte/sec, 2 block align, 16 bits/samp
sox: Output file test.wav: using sample rate 8000
        size shorts, encoding signed (2's complement), 1 channel
sox: Output file: comment "test.au"


*******
The resulting file sizes are then:
-r--r--r--    1 marit    marit    527881224 Jan  6 15:43 test.au
-rw-r--r--    1 marit    marit    191521568 Jan  7 19:13 test.wav

I am open to any suggestions.  I wasn't expecting 3.5 hours of
low-quality audio to be 200 MB, but maybe I am naive.  Am I using the
wrong tool?  As a separate question: How much space would I save using
mp3 or ogg encoding?

Thanks in advance,

Ben Blout