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These days many people store their music digitally on a computer or home server. This music may be purchased on CD, downloaded from the Internet, or even digitized from a high quality source such as a vinyl LP record. The format and sampling rate used can have a big impact on the quality of the result.
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The Formats Available
There are three principal ways to encode audio data: uncompressed, lossless compression and lossy compression. There are proprietary platform-dependent versions of each. Uncompressed audio is most commonly seen as either the .WAV format for Windows or .AIFF on the Mac. The quality will depend upon the sampling rate. The original sampling rate for CD audio was set at 44.1 KHz, designed to exceed double the highest audible frequency. Each sample was represented using 16bits. More recently, a limited amount of material has been made available in higher quality, sampled at up to 192 kHz and using 24 bits. Companies such as Linn and Naim offer direct download of their own recordings for direct replay using home computers or servers.
Lossless compression is designed to store music more efficiently whilst maintaining the integrity of the signal. These compression algorithms are designed to allow the signal to be reconstructed bit for bit compared to the original. They can achieve a compression rate of 2-3 storing a typical CD occupying 600Mb in uncompressed form in around 250-300Mb depending upon the complexity of the signal. Examples of lossless compression are WMA Lossless for Windows, Apple Lossless for the Mac (and iTunes even when running under Windows) and FLAC as an open-source alternative.
Lossy compression achieves higher compression rates by effectively removing the parts of the signal that are unlikely to be heard. The compression rates achieved vary according to the sampling rate chosen but are typically up to 10 times storing a CD in around 50-60Mb. Examples of this type of compression include MP3, the most common format of all, as well as WMA for Windows, and AAC (used in the M4p file format) used by Apple in the iTunes store.
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Which Format Should I Use?
The best format to use is dependent upon your situation. The key factors are quality, storage size, and delivery environment. Thus, if your preferred environment is iTunes on your computer and an iPod or iPhone for portable use, then you will be effectively limited to either Apple Lossless or AAC. iTunes provides facilities to convert other formats. For serious home replay or for use with iPods with upgraded headphones or a high quality dock, Apple Lossless is a good choice offering high quality replay. If you are limiting your use to a standard iPod, then the AAC format will allow you to fit more songs on your portable player.
For more general use and maximum quality and flexibility, the FLAC format offers an open route to lossless coding. Whilst it is not offered within iTunes, it is increasingly available as part of open source music applications, and can be used with Windows Media Player if a plug-in is downloaded such as this one. Applications such as Songbird enable you to manage your FLAC encoded audio files in an open source iTunes like environment. Other applications, such as dBPoweramp, offer a convenient way to rip music from your CDs in FLAC format.
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For many home users, iTunes and Windows Media Player offer convenient ways to manage digital audio. Once your music is replayed through a decent music or home theater system, the default formats used by these applications may seriously compromise replay quality. This quality cannot be reinstated once it has been lost, so some thought is needed to get the best sound. And finally, always remember to stay within copyright laws for your jurisdiction.