Compression, Ripping, Encoding

Compression

With the popularity of the personal computer (utilizing digital storage) and a most explosive mode of communication and information transportation with the internet introduces the ability of audio storage and transfer to the end user - which was previously limited to tape dubbing. Also, the "collaboration" of available software ("CD ripping" or "CD extraction" software) with a computer CD-ROM and hard drive now has the ability of copying the information stored on a compact disc onto the local hard drive with absolute, 100% accuracy.

As impressive as this ability of "copying" may be, the size of this audio information is enormous in comparison to the various methods of transportation currently available. Some may ask "how big?" and for them the following information is mathematically deduced:

  • the format of digital audio storage used in a compact disc utilizes 1441.2 kilobites per second (kbps)
  • this is achieved by: 2 channels (left and right channels) x 44.1 kHz x 16 bit = 1441.2 kbps.
  • this format outputs approximately 10 megabites per minute of audio.

A filesize of this magnitude would take the average modem user about 35-50 minutes to transfer only one minute of music. Now realize the average length of a song (usually ~3 minutes before 1970 and approximately ~4 minutes afterwards) and you have one song that will take at least 1 1/2 hours to 2 1/2 hours to transfer via dial up internet connection (which was the only available mode of connection until recently). the complications of transferring such a huge file size spawned the use of two different types of compression techniques, lossless audio compression and lossy audio compression (also known as "psychoacoustic audio compression").

Shortly saying, audio compression is a process which aims to reduce the amount of data required to store the music. The two possible approaches to this are lossless compression and lossy compression. the similarities of lossless and lossy modes of compression end at their shared objective - to decrease the filesize of an audio file while maintaining quality. A quick explanation of the differences between the two formats would be that lossless audio compression is, by definition, a compressed audio file that can be decoded to result identical to the source wave file, whereas lossy audio compression cannot be decoded to result identical to the source file, ever.

Ripping

The process of saving the content of a CD to a computer harddisk is called ripping.

Why is the ripping tool important? Isn't it just a transfer of digital data? A CD contains digital data in raw format which does not have any error correction features like checksums which are standard with all other computer files. What this means is that you can never be sure that you have successfully copied all the digital data. What software products like EAC do, is read each sector several times and only "approve" of it if the result is always the same. This results in a longer ripping time but also in a better quality.

What sometimes happens with lower quality ripping tools is that you have drop outs in your music files. The ripping speed very much depends on the CD and your CD-ROM/DVD drive.

Encoding

The process of transforming an audio file from .wav to a compressed format (.mp3, .ogg) is called encoding. This is a very CPU intensive task and the faster your computer you perform the encoding on, the better. If you have a slow processor in your jukebox, it is a good idea to do the ripping on your main computer.

It is also a good idea to batch encode your .wav files when you don't work on the computer. This is very easy with programs like Monkey's Audio for lossless or with Razorlame for lossy MP3 formats. You won't waste any time waiting for the task to finish during ripping.


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