Guide to Digital Audio Compression

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AudioReview.com's Guide to Digital Audio Compression

This is a follow-up to our previous article on pc audio hardware and software.

Last time we covered pc audio hardware and software and here we will cover compression formats and their effect on sound quality. How you store your music is as important to sound quality as is the hardware.

Compression Formats: Quantity vs. Quality

Basically, it boils down to the old question of quantity vs. quality. Music files as they exist on your CDs are very large – one CD uses about 700 megabytes (MB) of space, nearly one gigabyte per CD, or 10 MB per minute of music – and would take up way too much space on your computers’ hard drive.

Since storing files uncompressed would require so much expensive hard disc space, we compress the files. The first compression format that enabled the PC audio revolution was MP3, and it continues to dominate today. MP3 is quite simply one format for compressing your music. Compressing to MP3 enabled you to store nearly dozens of CDs worth of music in a very small space. Hence MP3 players, and file sharing were born.

Problem was, these highly compressed files sounded like absolute garbage. The early compression process very crudely ripped out parts of the music, giving you a distorted and ugly representation of your music. Audiophiles shunned PC Audio altogether.

It turns out those highly compressed files were to blame for bad sound. New compression technology and better PC sound cards have given way to renewed interest in computer audio.

Where to Start

First, you need to secure as much hard drive space as possible. At least several gigabytes worth, or even up to several hundred, depending on the size of your collection and the compression rate you choose to use.

Next, you must choose a music management software with a “ripper� to extract the music files from your CDs and convert them into music files. See our previous article for a guide to choices on music management software.

Your two main choices will be “lossy� and “lossless� compression formats. They are pretty self explanatory. “Lossy� compression removes parts of the music that the compression software deems unnecessary or inaudible. This includes high and low frequency information. The more compression you use (to get smaller files) the more music you will lose, and the worse your music will sound. Obviously the advantage here is that you can fit a lot music into a smaller space. With lossy compression, however, you have many options how you compress your files. You can use low compression rates which are larger and discard less of your music in the compression process. You can also use Variable Bit Rate encoding, which intelligently decides which musical passages require more space, and and which less, instead of uniformly using the same compression rate across a track.

The other option is Lossless encoding. Lossless compression is the best compromise for people who can't bear to have their beloved tunes hacked up by a piece of software, but don't want to give up tremendous amounts of disc space. That said, lossless compression still uses quite a bit of space, about 60% of an uncompressed .wav file. Remember, a .wav file consumes about 10mb per minute of music. The sound of a lossless file is indistinguishable from its .wav counterpart.

Here’s a breakdown of various compression options:

Lossy Compression Formats:

MP3. The "Industry Standard". Just about every player supports this format. This is often what you'll find if download music online, and gives you the most options in terms of encoders and playback software on your computer. Some say that MP3 has been outpaced by newer, better sounding formats such as WMA, AAC, and OGG. If you choose this format, try and use "Variable Bit Rate" MP3 encoding. This is a smarter method of encoding which consumes more drive space on more complex parts of a musical composition, where there's more information, and less in quieter or less complex passages.

WMA. Microsofts' proprietary format. Reportedly it is a quality format but not many players are supporting it. If you choose to use this format you are committing to the microsoft format. Your choices will be limited to a few players and companion software for your computer.

AAC. Apple's proprietary format. Much like Microsofts' WMA, it is a newer, good quality format, but it restricts you to Apple's iPod and iTunes software, and little else. If you use Apple's iTunes online music store, the songs you download will be encoded in this format.

Ogg Vorbis. A fairly popular open source compression format reputed as having very good sound quality. Somewhat limited player support, however.

ATRAC. Sony's proprietary compression format. If you are going to buy a Sony player, such as their Network Walkman (NW-HD1), you can only use this format. More on this in the player guide section - remember beta video tapes, anyone?

Lossless Compression Formats:

Apple Lossless. Apple's proprietary lossless format is getting good reviews, but again, you are pretty much restricted to Apple products.

FLAC. Open Source, revered among audiophiles for its sound quality. A popular format, but not too many players support it.

-Good Luck!

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