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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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