When mastering music, try to avoid changes to your signal greater than 3dB when equalizing the signal, and avoid very narrow bands or curves. Additionally, some subtle tube or tape saturation and very mild compression prior to limiting to control your dynamics and create a full sound.
The purpose behind mastering music is to prepare a recording for consumer-grade equipment - this means that the master should adhere to the technical limitations of the equipment or specifications of the medium. Typically when mastering, we want to retain the mix’s timbre while increasing its perceived loudness.
Any changes made to the signal during mastering should be minimal, improve the sound and enjoyability, and be made as objective as possible.
When equalizing a master, try to avoid any changes greater than 3dB - also, I find that using subtractive equalization first is helpful. Furthermore, I typically avoid very narrow bands since this results in an unnatural sound - whereas a 1-octave bandwidth or a Q value of 1.414 will sound musical.
Try low latency linear phase processing, or natural phase settings if available, since zero-latency may cause unwanted boosts or dips to your signal.
In many instances, you won't need to compress a master since the mix will already be compressed enough, however, if you’re trying to achieve a louder master, or glue details together, use compression. My favorite method is to use an internal side-chain filter to ensure the lows don’t trigger compression.
Then I’ll time the compression to my host BPM using 60000/BPM as my formula. This value or a half or quarter of this number will be my release time.
To saturate a master you need to use both soft-knee compression and harmonic distortion or use a saturation plugin that combines the effects. For a warmer-sounding master, use a tube saturator - for a cleaner, slightly clearer sound, use a tape or transistor saturator plugin.
To see what harmonics you’d add to a signal with a particular saturator, run a sine wave through the saturator and see what harmonics form with a frequency analyzer.
Exciters are frequency-specific distortion plugins that target the high frequencies, in turn adding clarity to your instrument or master. The best way to add this is with a dedicated exciter plugin - which is somewhat rare but some good options are the Logic stock exciter, and Fresh Air by Slate.
When mastering keep this effect subtle - since you’re working with the full stereo track, excitement can become aggressive much sooner than you expect.
Of the many ways to add detail to a master, my favorites are low-level compression and parallel compression. In fact, you can combine the two for an interesting effect - first set up your aux send, then heavily compress; next introduce low-level compression to bring out the detail.
Then blend the compressed send back in. This is an unorthodox method, but it accomplished both downward and upward compression, resulting in a unique sound.
You need to be particularly careful when using stereo expansion on a master since some forms cause aggressive and unwanted phase cancellation. I personally prefer to use mid-side equalization, or mid-side compression to achieve a wider stereo image since I find these to sound most natural.
For a more vintage sound, use crosstalk on a tape machine plugin to widen your image.
Limiting your master can be difficult since you want the master to sound commercially loud, but while preserving the original timbre, dynamics, and transients as much as possible. For a louder sound, you may need to sacrifice some of these elements by using the limiter aggressively.
A good starting point when limiting is using a 50ms release time, achieving roughly 3 to 6dB of attenuation, setting a ceiling of -1dBTP, and using at least 4x oversampling if available.
When measuring your master, a true-peak meter measures the level or peaks, and a LUFS meter measures the signal’s perceived loudness. Ideally, your dBTP will be around -1, and your LUFS will be somewhere between -16 LUFS for dynamic genres, and -7 LUFS for loud genres.
Loudness normalization will play a role as well and may turn your track up or down before streaming, so keep that in mind when determining levels.