What audio file format should you be using? Mastering engineers typically request their clients to send them their final mixes in either WAV or AIFF format. Why? The following table provides a simple explanation.
| Format | Extension | Lossless? | Use For Mastering? |
|---|---|---|---|
| WAV | .wav | Yes* | Yes |
| AIFF | .aiff | Yes | Yes |
| MP3 | .mp3 | No | No! |
| OGG | .ogg | No | No! |
| M4A | .m4a | Maybe | No! |
WAV and AIFF are the only two common audio file formats that do not compress the audio signal to save space. Here, by "compression" we mean audio file compression (e.g. MP3 file compression) not audio signal compression (e.g. using a glue compressor). Audio file compression reduces the file size significantly (e.g. to one tenth of the uncompressed size) in exchange for the introduction of a small amount of distortion to the audio signal. Mastering engineers want to operate at an excellent audio quality level, and do not want the mastering process to introduce unnecessary distortion, so they typically require their clients to provide their final mix in either WAV or AIFF format.
Note: MP3 files come in a variety of compression levels, and some of the less-compressed levels approach WAV/AIFF quality.
* WAV files are actually also capable of storing audio in a compressed format (see the wikipedia page), but in practice almost never do.
For more information on audio file formats, see the Wikipedia Audio File Formats Page.
Within the WAV or AIFF file, the signal is recorded at a sample rate. Here are the common sample rates:
| Sample Rate | Comment |
|---|---|
| 44.1KHz | The industry standard sample rate. This is used on CDs. |
| 48KHz | A higher quality sample rate that is better than 44.1KHz. |
| 96KHz | A high quality sample rate. Reduces audio plugin aliasing. |
| 192KHz | A very high quality sample rate. Reduces audio plugin aliasing. |
Mastering engineers typically require a minimum sample rate of 44.1KHz. This is fine, but we like to work at 48KHz because 48KHz halves the slope of low-pass filters applied arounds 20KHz (Nyquist 24KHz vs 22KHz) which, in turn, reduces aliasing.
Within the WAV or AIFF file, each sample is recorded with a particular bit width. Here are the common widths:
| Sample Width | Comment |
|---|---|
| 16 Bits | The old industry standard sample width. It is used on CDs, but is now considered not high enough quality. |
| 24 Bits | The new industry minimum sample width for audio professionals. |
| 32 Bits | Excellent quality, but 24 bits is good enough. |
Mastering engineers nowadays typically require a minimum sample width of 24 bits.
Here's what you should be using for your professional audio production. This is what we would like you to send us when you upload a final mix for mastering.
| File Format | AIFF or WAV. |
| Sample Rate | 44.1KHz or higher. |
| Sample Width | 24 bits or higher. |
If, for some reason, your final mix does not satisfy these requirements (e.g. it's a high-quality MP3), we can still master it. The quality of the final product just might not be as high.
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