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Subject: RE: Question about CD-Quality and MP3

RE: Question about CD-Quality and MP3

From: rob powell <rob_at_rinty.plus.com>
Date: 2006-02-01

Hi,

Not sure I understand the question entirely, but here's some help.
Hopefully it'll be of use to others too.

These comments are obviously not all-encompassing, but they do to gain an
understanding. There are 2 elements to the quality of a digital audio file,
whether it be MP3, Ogg, or whatever. Sample frequency and bit rate.

First, professionally produced audio CD's are always sampled at 48KHZ,
whereas most MP3's and minidisks tend to be sampled at 44KHZ. Second is the
bit-rate, not so critical as the sampling rate, but still important. Most
MP3's are recorded at 128KBPS, (kilobits per second), though of course you
can record at whatever value you want, provided your MP3 player will support
it). I for example record books at 48KBPS, 22K sampling rate, and mono.

It's generally agreed however that to obtain CD quality, you need to be
recording MP3's and any other audio format for that matter at 192KBPS. For
reasons that I'll go on to explain, it's not actual CD quality, but it's
recognised to be audibly very close, and barely noticeable.

There are basically 2 types of digital audio formats, lossie and lossless.
Lossless create larger files, lossie ones smaller. .MP3 .ogg and .wma are
examples of lossie formats, .wav is a lossless format. The issue is not
whether you loose anything by converting to MP3, but whether you'll notice
what you loose on the equipment you're using for playback. 44KHZ and 128KBPS
are generally recognised to provide an adequate level of playback for
portable digital audio devices, and indeed I find that generally to be true:
however when I connect the Archos or Iriver to my hifi system, I can hear
the difference quite easily between the CD and the music on my player.
Basically it's horses for courses.

Inevitably however there's a trade-off between file size and quality. You
don't actually need an audio book (speech) to be the same quality as your
favourite album: so you can get away with lower bit-rates and sample
frequencies, which mean smaller files, and less space on your MP3 player. I
change the bit-rate and sample rate quite a bit, depending on what I'm
recording. Old football matches recorded from AM don't need to be recorded
at a high bit rate and sample frequency, as the bandwidth of AM limits the
quality of the original. Well-recorded stereo radio dramas however benefit
from higher recording quality.

The generally accepted rule is, that the MP3 standard is good for many
reasons, not least because all digital music players will play it. However
Ogg Vorbis WMA and others have advantages. Ogg Vorbis files take up less
space for the same sample and bit-rate size. It's also a more modern
encoding standard, and therefore the quality of a file will be higher if an
MP3 file and an Ogg Vorbis file of the same size are compared. However a
.ogg file and an MP3 file recorded at the same bit-rate and the same sample
rate will be of very similar quality. That's as I understand it, if I've
got it wrong, I'm happy to take corrections: as I'm a bit hazy there.

Gary, you might know more.

   I think that all the units that'll take rockbox are capable of reading
files from 32 to 320KBPS, and with sample rates of 22 to 48KHZ.

In short, the lower the bit rate and sample frequency, the smaller the file,
but the poorer the playback quality.

HTH,

Rob

-----Original Message-----
From: rockbox-bounces@cool.haxx.se [mailto:rockbox-bounces@cool.haxx.se]On
Behalf Of Selamet Aydogdu
Sent: 01 February 2006 09:32
To: rockbox@cool.haxx.se
Subject: Question about CD-Quality and MP3

Hello,

I search some sources that describe the different about MP3 and CD-Quality.
If it's possible that you can hear the same sound in MP3, that exists too in
CD-Quality? Whats about OGG?

Greetings
Selamet

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Received on Wed Feb 1 11:17:26 2006

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