Audio files are broken down into two different groups — uncompressed (lossless) and compressed (lossy). Uncompressed file formats are used when maximum audio quality is desired. While analog purists will argue that digitizing any signal results in a loss in quality, lossless audio files try their best to keep all the digitized data in its full form. In general terms, you’ll want to use lossless formats when the audio may be further edited or passed through other computer processing. Files that have been compressed with lossy codecs will only be degraded further if they are subject to additional computer modifications. Compressed formats are used when the highest-quality audio is not necessary or when storage space and transfer time are important considerations.
Uncompressed Audio Formats
AIFF
(Audio Interchange File Format). These files will often use the .aif extension. This is a noncompressed format that is used to store audio files primarily on Apple computers. However, most PC software can read AIFF files without a problem. The AIFF format was developed by Apple (some folks believe that the acronym stands for Apple Interchange File Format) and was based on the Electronic Arts Interchange File Format. One of the advantages of this format is the large amount of nonaudio data that can be stored along with the audio information. AIFF files often contain information such as name, author, copyright, and comments. As is an uncompressed, lossless format, it takes about 10MB to save a minute’s worth of music.
WAV
(Waveform Audio Format). The common extension for this type of file is .wav. This is a file format designed to store audio data on PCs, yet most Mac software will also open WAV files. While this format is a close cousin to AIFF, it makes some use of the special features available with Intel CPU machines. WAV files can hold audio that has been compressed, but they are most often used to house noncompressed audio. Due to the limitations of the format, WAV files can’t be larger than 2GB. It is also an uncompressed, lossless format, and it takes about 10MB to save a minute’s worth of music.
Compressed Audio Formats
All compression formats use a codec of some sort. An audio codec is a process or a software program that compresses (co-) and then decompresses (-dec) an audio signal based on a number of rules and assumptions about how we perceive music. Compressed audio is further divided into codecs that are lossy and those that are lossless. With lossless audio compression formats, the size of the file is reduced but the quality of the music remains the same. In theory, the decompressed signal is exactly the same as the original signal. While lossy compression formats can offer a huge reduction in the file size, you can expect only about a 50-percent reduction when using lossless codecs.
AAC
(Advanced Audio Coding). Apple’s default audio format, AAC is a lossy compression scheme that was developed to be an improvement over MP3 and designed for audio streaming. Some argue that AAC produces the same quality audio at 96 kbits/s as a mp3 does at 128 kbit/s. Some of the features that make AAC more robust than MP3 are the ability to sample frequencies from 8 Hz up to 96 kHz, the use of up to 48 channels, and higher coding efficiencies for stationary and transient signals. The AAC file format was first published in 1997 but came into the popular consciousness when Apple computer’s iPod began using this file format in 2003. With the recent developments in mp3 codecs, mp3s have performed far better in listening tests against AAC than in previous years. Nevertheless, when it comes to a sound quality to file size ratio, AAC beats MP3.
ASF
(Advanced Streaming Format; later changed to Advanced Systems Format). This file format is patented in the US by Microsoft and is used by Windows Media for both audio and video. ASF files are more like containers that can hold data compressed by a number of different codecs. WMA (Windows Media Audio) and WMV (Windows Media Video) are the two most common file types held inside an ASF file.
ALAC
(Apple Lossless Audio Codec). This format is also called Apple Lossless Encoder, or ALE for short. Similar to ASF files, ALAC files serve as a container to house files that have the extension m4a. This format was first introduced in a QuickTime upgrade in 2004 and implemented into Apple’s iTunes 4.5.
FLAC
(Free Lossless Audio Codec). The “free” part of this file format’s name means that the FLAC process is not covered by any patent. Like other lossless compression formats, FLAC can reduce an audio file by 30 to 50 percent. FLAC files are becoming more popular as a way to archive CD collections and as a way to transfer high-quality audio over the Internet. FLAC files can be read by a number of different programs on all major computer platforms.
m4a
(MPEG-4 Audio Standard). This is the file extension of an audio file that uses MPEG-4 Advanced Audio Coding. Apple made this format famous by using it for their iTunes software. Most software that will read MPEG-4 files will support the m4a format.
MP3
(Moving Picture Experts Group-1 Audio Layer 3). Without a doubt, this is currently the most popular audio compression format on the planet. The MP3 audio compression format was first developed as early as 1987 and finalized in 1992. The first commercial software to use the MP3 format was Winplay3 in 1995. Since that time, MP3 files started appearing on the Internet, and as they say, “the rest is history.” Today, the number of applications that can read or write MP3 files is enormous. It is the ubiquitous standard for sharing audio files over the Internet, and for good reason. It’s fast, it’s free (for the user), and it can drastically reduce the size of an audio file without totally destroying the quality. Like other lossy compression schemes, it does this by removing portions of the audio image that the algorithm determines can’t easily be heard. MP3 files can perform their compression magic at a number of different bit rates that can adjust the trade-off between file size and audio quality. Common bit rates range between 32 and 320 kilobits per second (Kbps), with 128 Kbps and 192 Kbps being the most popular compromise. For most civilians, an MP3 file at 128 Kbps will sound just fine. If you’re planning on listening to music files in a moving car, 128 Kbps might satisfy your ear. But for most musicians who are familiar with the sonic fingerprint of high-quality instruments, a 192 Kbps format or higher is often necessary.
OGG
.ogg – Vorbis, which is the name of Ogg’s audio format, is an open source lossy compression format that is favored by developers of free software for its patent-free nature. Despite its claims of being able to produce better sounding music at smaller file sizes, Vorbis is not widely used because of its slow encoding time and the lack of native support from popular music players such as iTunes and Winamp. However, many video game makers and programmers have begun using Vorbis because it is open source, and thus does not demand licensing fees like mp3 and aac do. If you are interested in testing the sound quality of Vorbis yourself, try the aoTuV modification of Vorbis and install the XiphQT plugin for iTunes.
WMA
(Windows Media Audio). WMA files are compressed files that are played using Microsoft’s Windows Media Player. Originally, the format was developed to be a competitor to MP3; it’s now a competitor to Apple’s AAC format. The newest version of WMA is 9.1 and contains codecs for multichannel surround sound and lossless support. WMA files are most often contained inside an ASF file.
Conclusion
If you’re willing to sacrifice the storage space, and have ears sensitive enough to tell the difference between a CD and a ripped track, go with .wav or .aiff. Otherwise, .aac and .mp3 encoded at bitrates above 256 kbit/s are indistinguishable from CDs for the average person. Vorbis performs the best at low bitrates around 64 kbit/s, whereas the LAME encoder for MP3 performs better at higher bitrates. Regarding VBR and CBR, the general rule of thumb is that VBR will produce better sound quality at a lower file size than CBR can.