Should I brighten a dull mix with EQ or saturation?

Measure before choosing

Look at the spectrum of the mix, or compare it with a reference track at the same loudness. If the top end rolls off gently, there is content to raise. If it stops, as it does on a dark synth, a bass or a recording made with a dull microphone, there is nothing for an EQ to work on.

Check the low-mids as well. A mix can sound dull because it has too much at 200 to 400 Hz, not too little at 10 kHz. Cutting there brightens the mix without touching the top.

Brightening with EQ

• A high shelf from 8 to 10 kHz, raised 1 to 3 dB, for air.
• A broad bell at 3 to 5 kHz for presence, in small amounts: this range becomes harsh quickly.
• Shelve single tracks before the whole mix. Brightening the master also brightens the hi-hats and the vocal's sibilance.

Brightening with saturation

Saturation bends the waveform, and that creates harmonics at multiples of the frequencies already present. A bass with nothing above 2 kHz gains upper harmonics that make it audible on small speakers. A flat pad gains texture.

• Use a little drive. The result should be heard as brighter, not as distorted.
• Blend it with the dry signal if the tone changes too much.
• Use oversampling on bright sources, so the new harmonics do not fold back as aliasing.

Both, in that order

Saturate the tracks that lack harmonics, then shelve the mix as a whole if it is still dark.

In Zammoth

The engineer measures the mix's spectral tilt and its balance across eight bands before it answers, so the reply says which case you have:

The EQ has high-shelf and tilt-shelf shapes. Saturation has 1 to 12 dB of drive, four curves (tanh, warm, tube, hard), a mix control and oversampling up to 8×. See the EQ reference and the Saturation reference.