Re: MP3 to OGG converters

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To: For users of Fedora Core releases <fedora-list@redhat.com>
Date: Sat, 11 Dec 2004 10:08:19 -0400

El vie, 10-12-2004 a las 18:01 -0800, Austin Isler escribió:
> All this talk of lossy codecs, so please inform us of a good codec.

MP3 and OGG codecs lose some information. I will exemplify with a picture (called pic A).
If you use a lossy compressor (like jpeg format), maybe you lose some stars in a
nightly heaven picture when decompressing to pic A'. (dont forget: codec means an algorith for
coding and decoding, you use it sually to transport your files, using less space, but when using
them at your destiny, files are decompressed)

pic A -> (losely compression) -> (decompression) -> pic A'

The idea is that the compressor makes his job so you cannot see the difference at first sight.
But, if you compress this again with a different algorithm, the process is

pic A' -> (losely compression) -> (decompression) -> pic A"

Pic A" has lost some stars again. But this time, you'll probably see the difference at first sight.
That is the problem, we want to lose all information we don't use, but not the one which we use.

MP3 is like a Pic A', cause it's got some loseness. Somebody suggested you to compress the file from the original,
that means you must not do:

.MP3 (1 level of loseness) -> .MP3.OGG (2 levels of loseness, noticeable) NO!!!!

and the best you can do is

.WAV (0 level of loseness) -> .OGG (1 levels of loseness, not very noticeable) YES!!!!

There also exists some loseless codecs, like FLAC. You can read about them, but the idea
is when making the compression and the decompression procedure, you obtain the same original file...

audio A -> (loseless compressed audio A) -> audio A (the same original)
ie
original .WAV -> .FLAC -> original .WAV

But theoretically, loseless codecs can't compress the same rate than lossy codecs.
Personally, I have a litle idea of the process, but can't notice the difference between a WAV and a
MP3-128kbps compressed file (what is that? a file that uses 128kb per each second of audio,
approx 1/10 of original audio size and more than 9/10 quality rate).

I can hardly feel the difference in a 112 kbps, when a cymbal crashes, paying some attention, but as I said,
that's a personal feel. So, theoretically I WILL FEEL THE DIFFERENCE if I make an .MP3.OGG
compression, cause a .MP3 has a 90% quality and a .MP3.OGG has 80%, using the same rates.
112 kbps is 87% of 128 kbps, so my .MP3.OGG will be less than 112kbps, say 102kbps. Probably I will
notice the difference. Some others don't. Some others say the quality of a MP3-128kbps file is
more than 95%, by using a comparison algorithm. I believe it's hard to find.

-- 
Rodolfo Alcazar (rodolfo.alcazar@padep.org.bo)
Administrador datos y red - Padep/GTZ
La Paz, Bolivia
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