When you hear compression you often hear the absence, rather than the presence of something.
The best gain control is performed using a fader; there's no artefacts or colour, it's the highest fidelity option.
Compressors Vs Limiters
Compressors allow you to work with longer time frames; limiters are a safety net to prevent distortion.
Compressors map better to musical signals than limiters. Anything that has a note to it is best suited to a compressor, as the release time is fractions of a second rather than milliseconds.
How Compressors Affect Level and Tone
Compressors don't make things louder; they turn things down. The reduction tends to thicken sounds.
While it does make sense to reduce dynamic range to create more headroom, enabling you to turn the whole track up, what you're doing is turning the level down so you can turn it up again later.
Compressors will often rob sounds of some early harmonics. Early harmonics are in a section of the frequency spectrum where our ears are most sensitive. A lot of harmonic content between 1 - 4kHz, will give you an increased sense of loudness according to our perception. When you compress, you're going to lose some of that signal unless you use a fast release time or a compressor that adds harmonic distortion. They're suitable for glue and punch, but they're not the thing that makes something loud.
How Compressor Affect Clarity and Density
You can think of a compressor as an envelope. You're shaping the sound over time. They're like transient shapers; they allow you to modify and shape a signal.
The trade-off, when using a compressor, is between transient and sustain. There's also a trade-off between clarity and density.
If you want a record to sound clear, you should be light-handed with a compressor. Do not apply much reduction, use meagre ratio's and long attack times to persevere the ability to distinguish between one element and another in a mix.
If you want a dense, wall of sound mix, a compressor can help bring everything together and give you what's called 'glue'.
How to Add Punch to with Compression
Punch = Bring the transients forward.
The recipe for this is letting the transient come through with a long attack time (50ms), quick release (100ms) and low ratio (2:1). These settings enable the compressor to allow the transient through before the rest of the sound is pulled up. In this example, the compressor isn't kicking in until 50ms has passed after the signal crosses the threshold.
50ms is an interesting number that corresponds to a 20Hz sine-wave signal. Anything preset when a transient hits that might cross the threshold will go through a full cycle before the compressor kicks in and interrupts it. Therefore, there's a relationship between the low-frequency component and the attack time. As the attack gets shorter, it's going to start pulling back the low-frequency transients, as it gets even shorter it begins to interrupt the transient shape as one moves higher up the spectrum.
As you reduce the attack time on drums, the transients begin to fold back into the overall mix.
A longer release time provides a smoothing effect.
How to Get Smoother Compression with Side-chaining
Use side-chains to remove low frequencies from a mastering compressor to effectivity compress the bass and everything else individually.
MV: I use a multi-band compressor to achieve the same results. One band for the bass and one for everything else. Same compression settings. Just different threshold levels.
Glue = Bringing everything closer together with a compressor, trading some of the transient energy to better hear the sustained information. You can use 1dB - 1.5dB of gain reduction as a thickening agent.
How The Compressor's Knee Affects The Sound
Softer Knee = More compression happening at a lower level, and a gradual onset of compression, which results in a smoother overall sound.
Hard Knee = Fast onset of compression as the signal crosses the threshold, which translates to a brighter sound, sometimes with a little distortion.
Soft Knee = Smooth
Hard Knee = Edginess
Compressors Detector Types
Peak = Looks at the peak level over a short period - tracks the fast-moving signal.
Peak = Drums/transients.
RMS = Track’s sustained elements.
RMS Window = 1/3 of a second or 300ms, typically tracks sustained notes.
You can change everything in the low band, say under 150Hz by just altering the attack time - as this will change the relationship between the kick and bass. A long attack time will let the Kick drum come forward and compress the bass, ditto for the opposite.