What Are Audio File Formats?
Audio file formats are digital standards for storing audio information. The raw data in a stream of audio from the analog-to-digital converter in your audio interface is encoded using a technique called PCM or pulse code modulation. PCM audio needs to be organized into a file so you can work with it, or play it back in a system.
Different audio file formats use different containers and varying methods of data compression to organize the PCM stream. Depending on which you choose, each format represents the same information in different storage sizes or quality levels. In addition to that, some audio file formats carry metadata that supplies information about the file or its content.
Lossless vs. Lossy Audio Files
There are two main types of audio file—lossless file formats, and lossy file formats. The difference between the two has to do with data compression.
Data compression means making the files take up less space on a hard drive. It’s not the same as the dynamic range compression used in music production.
Some methods of data compression make the file smaller but still preserve 100% of the information in the raw audio stream. These are known as lossless compressed formats.
Other compression types work by eliminating data in the audio that doesn’t make a big impact on the sound. Some information is thrown away using this method, so these are known as lossy compressed formats.
Uncompressed Audio Formats
There are other audio file formats where no data compression is used. These are called uncompressed audio formats. These file types act as a container for raw audio data without reducing its size or quality in any way. These are the largest files to work with, but they provide the highest level of detail in the audio information. Uncompressed audio files are the type most often used for recording and mixing music in a Digital Audio Workstation (DAW).
Even so, uncompressed audio files also come in different quality levels. These are based on the accuracy and precision with which the analog audio signal was converted to digital. The higher the sample rate and bit depth used, the more information is captured in the conversion process. Bit depth represents the precision of the AD/DA converter for measuring amplitude, or the volume level of the signal.
You can think of it like the number of tick-marks on a ruler—the more closely spaced they are, the less often the measurement will fall in between the two marks. Sample rate means the number of times the measurement is taken in a second. Higher sample rate means more individual measurements made.
Here is a list of common quality levels for uncompressed audio:
Audio Bitrate
Lossy compressed audio files can be encoded at different quality levels. The quality of this file format is determined by the bitrate, or the amount of data encoded per second. At lower bitrate settings, the compressed files will be much smaller, but may sound worse.
In the past, this was necessary since storage media had limited capacity and networks couldn’t easily transmit large files. But storage and bandwidth aren’t so much of a concern in today’s digital world. That’s why a larger file with higher bitrate is almost always the best choice when you need to use a lossy format.
A high quality standard for MP3 compression is 320 kbps. At these settings it’s very difficult to distinguish compressed audio from uncompressed in casual listening tests.
Common Audio File Formats
There are many different file formats out there, but not all of them are widely used. In fact, there are only a handful that you’ll commonly see in the wild.
Here are the main ones to know:
MP3 / M4A
MP3s are the most common file type for general listening.
The use of MP3s exploded during the file sharing revolution of the early 2000s. The reason why has to do with the sound quality they were able to achieve in such a small package.
MP3s were the first audio file format that made music easy to send back and forth across the internet in listenable audio quality.
MPEG-4 is a multimedia container format that supports video, audio, subtitle, and image data encoded in different codecs. MPEG-4 files that store video are saved as .MP4 files. However, if the MPEG-4 file only stores audio, it is saved with the .m4a extension, which stands for “MPEG-4 Audio.” This name change helped distinguish between MPEG-4 video files and MPEG-4 audio-only files.
You will most likely encounter M4A files when downloading audio content via the Apple iTunes Store. The content, most typically songs, is encoded with AAC compression, which significantly reduces the size of each file. Songs that include copyright protection have an .M4P extension.
AAC
AAC is a lossy compressed format designed by a group of digital technology companies including Dolby, Microsoft and Bell . It was intended as a more efficient successor to MP3. AAC is known for being the standard format for Apple devices like the iPod.
If you ever bought music on the iTunes store, or used iTunes to rip CDs to your library, you might have some AAC files lying around.
Ogg Vorbis
Ogg Vorbis is an open source alternative to lossy compressed formats like MP3. It’s notable for being the file type used for audio material on Wikipedia.
Despite its widespread use, MP3 is a proprietary format. In response, the open source community created Ogg Vorbis as an alternative that’s free and editable.
FLAC
FLAC is an open source lossless compressed file format. It was one of the first lossless compressed formats to gain popularity. FLAC files make listening to lossless audio possible on devices with limited storage.
WAV / AIFF
These are the most commonly used file types for working with lossless uncompressed audio.
Since there is no change to the amount of information included, both file types have similar performance.
WAV was created for use on PC, while AIFF was developed by Apple for the Mackintosh. Both formats are compatible on either platform.
Sound Fonts
A file format that contains samples of musical instruments as well as support for numerous music parameters.
Soundfonts enhance MIDI playback, because unlike the General MIDI standard, which describes how one hears the sound, Soundfonts include actual digitized sound waves stored in wave tables (wave table synthesis).
MIDI
MIDI is an acronym that stands for Musical Instrument Digital Interface. It’s a way to connect devices that make and control sound — such as synthesizers, samplers, and computers — so that they can communicate with each other, using MIDI messages.
MIDI files can also be created and/or downloaded which will consist of the notes of a song but without any sounds, but is capable of playing those notes with any instrument you prefer.
How To Choose An Audio File Format
With the background info out of the way, here are the simple guidelines for choosing an audio file format:
- For music production, use uncompressed audio with high sample rate and bit depth (24 bit / 48 kHz WAV or AIFF)
- For general listening, choose a high bitrate compressed format (320 kbps MP3, AAC or similar)
- For critical listening, choose a lossless compressed format (FLAC)
Hot Tip: No process in music production can add audio quality back if it didn’t exist already. To get the highest quality file, you need to start with a high resolution file. We recommend setting your DAW sessions to at least 24 bit / 44.1 kHz, or higher if possible.
Source: https://fileinfo.com/extension/m4a