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

[Frank Neumann]

Hi,
On Tue, 7 Jan 2003 19:37:39 -0500 (EST) ben-extra at MIT.EDU wrote:

[..]

> 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?

There is no mistake. It's a simple calculation: 3.5 hours is 210 minutes
or 12600 seconds. 8000 samples per second, each sample being 16 bits (or
2 bytes) gives: 12600*8000*2 = 201600000 or 200 MByte.

Personally, my suggestion would be to go for a lossy format, and try
Ogg/Vorbis (http://www.vorbis.com) which is supposed to be very good
especially at low bitrates. Typically an .ogg should be about 1/10th
of the original filesize, with low bitrates probably even lower than
that (but my experiences are with CD quality, not with mono/8kHz
material).

Hope that helps,
Frank