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Compressed Audio File Formats
There are two major categories for music files resulting
from an analogue to digital conversion process, lossless and compressed
(also called lossy). The lossless files are large files that contain
full digital equivalent of the original analogue sound. Compressed
files use digital technology to remove 'un-needed' elements of the
larger files. Typically you would burn a lossless file (WAV format)
to a CD to be played in a CD player, but for use within an MP3 player,
mobile 'phone or PC, a compressed file such as MP3, WMA or Ogg Vorbis
may suffice.
What is MP3?
MPEG1 Audio Layer 3 (MP3) is an audio file format
that aims to provide near-CD quality audio at a fraction of the file-size.
CD quality audio (WAV) files carry a lot of extraneous information
for frequencies outside human hearing, one of the ways that MP3
audio is able to compress data is by removing some of this information.
MP3 can be further compressed by lowering the encoding bit-rate,
the most popular files are encoded using 128kbps (kilobits per second).
Compression rates vary from 8kbps at the lower-quality end (suitable
for speech), up to 256kbps giving quality comparable to CD.
Typically an MP3 encoded at 128kbps will be approx
1MB (megabyte) per minute of audio. This can be compared to a similar
WAV file (CD track) which will be approx 10MB per minute, hence the
popularity of MP3 - you get a comparable quality for a tenth of the
size taken up on your hard-drive. A typical 3 minute track will be
of a size which can be emailed to friends or downloaded from the internet
by just about anybody (even on dial-up).
A conventional CD holds 700MB, around 70 minutes of
WAV-sized files, whereas if you store MP3s on a CD you get around
twelve hours of music. If you store your MP3s on a 4.7GB (gigabyte)
DVD , you can get a massive 78 hours of music time - that's more than
three days....
MP3 players are also very popular, even a cheap 128MB
MP3 player should be able to hold two hours of music.
What about OGG VORBIS?
OGG VORBIS is another format used to store digital
music in a similar way to MP3. The main difference with OGG VORBIS
is that it is completely free and unpatented. This means that licensing
restrictions which apply to MP3 and other formats, do not apply for
files using OGG VORBIS format.
Vorbis is inherently variable bit-rate, giving better
sound quality for a given average bit-rate, but not strictly adhering
to that average as a target. Nevertheless, comparisons can be made
using approximations based on the average bit-rates. Vorbis uses a
quality scale of q0 to q10, with q10 as the highest quality and largest
file size. This scale can be used for comparison using the following
guide:
q0 = 64kbps, q5 = 160kbps, and q10 = 400kbps
Very-near CD quality can be achieved at q5, the default setting
is q3, roughly equivalent to 110kbps. Many people agree that a Vorbis
file remains indistinguishable from the original source material
at q5 (~160kbps), whereas for MP3 a bit-rate of 192kbps is required
to reach the same standard. Put simply, that means that Vorbis should
sound better at the same file size as an MP3, and to achieve the
same sound quality as MP3, a Vorbis file will invariably be smaller.
Industry support for Vorbis exists in the form of
patches for Apple Quicktime (Mac & Windows) and Windows Media
Player enabling these popular applications to interpret Vorbis files.
Vorbis is also well-supported on the Linux platform. Several digital
audio player manufacturers including Samsung, Rio etc.. support this
format and many mainstream games producers have used Vorbis due to
the smaller file size and lack of licensing costs.
(source: Wikipedia and Vorbisdotcom)
So what in the world is M4P then??
M4P is a file format that contains a level of protection for copyright
purposes via DRM (Digital Rights management). This file format is
used by Apple iTunes and would need to be converted to work on a
device other than an iPod or on a PC using iTunes. There are some
software solutions for carrying out this conversion, some of which
have free trials. Up to the time of writing this section there is
no completely free software that I know of that will convert M4P
to MP3 orWMA/AAC etc..,
iTunes use a lossy format (compressed), to convert
to another lossy format (MP3 etc..) is likely to lead to further reduction
in audio quality. What this means is that if you pay for an M4P or
MP3 file download, be aware that you may not be getting anywhere near
the audio quality of a 'lossless' CD or WAV file. Buying a CD enables
you to create lossy files of varying audio quality, buying a lossy
file leaves you stuck with a lower quality product.
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