Definition
Masking occurs when one sound makes another sound that is close in frequency and plays at the same time less audible (or inaudible). It is the main cause of “muddy” mixes: it is not that the instruments are too quiet, it is that they cover each other. (Temporal masking is covered in “Psychoacoustics in mixing”.)
How the ear works
The inner ear analyzes sound in critical bands (about 24 bands along the audible spectrum, Bark scale): roughly 100 Hz wide below 500 Hz and about a third of an octave above. Two sounds in the same critical band compete; the louder one dominates. Masking is also asymmetric: a low sound masks the frequencies above it much more than those below (upward spread of masking). Practical consequence: excessive lows and low mids mask the clarity of the whole mix.
Typical conflict zones
| Conflict | Zone | Typical solution |
|---|---|---|
| Kick vs bass | 40–120 Hz | choose which one sits below, sidechain, complementary EQ |
| Bass vs guitars/piano | 100–300 Hz | HP on guitars and piano, cut on the bass at 200–250 Hz if needed |
| General mud | 200–500 Hz | small cuts on several tracks (−1/−3 dB) instead of one big one |
| Vocal vs guitars/synths | 1–4 kHz | carve 2–3 kHz on the instruments, dynamic EQ in sidechain |
| Vocal vs cymbals | 5–10 kHz | de-ess, cut the cymbals at the same frequencies as the sibilants |
| Snare vs vocal | 1–3 kHz | move the snare's presence to 4–6 kHz and its body to 200 Hz |
Strategies (in order of effectiveness)
- Arrangement: changing the octave, voicing or entry point beats any EQ. If piano and guitar play the same chord in the same register, move one of them.
- Sound choice: a darker pad, a thinner guitar.
- Complementary EQ: where one element has a boost, the other has a cut (see “Slotting and interlocking”).
- Dynamic EQ / sidechain: the cut happens only when the priority element plays (e.g. −3 dB at 2.5 kHz on the guitars when the vocal sings). Tools: FabFilter Pro-Q 3/4 (dynamic bands with external sidechain), Wavesfactory Trackspacer, soothe2, iZotope Neutron (Unmask).
- Volume sidechain (ducking) for the lows.
- Panning: separating in stereo reduces masking (but does not solve mono).
How to find it
- Listen to one element, then add the other: if the first one “disappears” or changes timbre, there is masking.
- Sweep with a narrow bell EQ (+8 dB, Q 4) to find common resonances, then go back to normal and cut.
- Analyzers with overlaid spectra (Pro-Q shows collisions with other instances).
- Listen at low volume: conflicts in the mids are more evident.
Example in A minor
Pop track at 100 BPM with piano (Am – F – C – G in the A3–E4 register), acoustic guitar (same chords in first position), pad and female vocal (E4–A5). Problems: piano and guitar mask each other at 200–400 Hz, both cover the vocal at 2–3 kHz. Solutions: guitar with a capo at the 5th fret and chords in inversion (higher register), HP at 120 Hz on the piano and at 180 Hz on the guitar, −2 dB at 300 Hz on the piano, dynamic EQ −3 dB at 2.5 kHz on piano and guitar sidechained from the vocal, pad with LP at 4 kHz.
In FL Studio
Fruity Parametric EQ 2 for static EQs and analysis; for sidechained dynamic EQ you need external plugins (Pro-Q, Trackspacer) or Fruity Limiter / Maximus as a sidechained multiband compressor (Maximus accepts per-band sidechain). Route the vocal to the instruments' sidechain with “Sidechain to this track” from the mixer's routing menu.
Common mistakes
- Mixing in solo: EQ in solo does not take masking into account.
- Cutting everything everywhere: a thin mix with no body. Decide priorities.
- Boosting the covered element instead of removing from the one covering it: it raises the overall level and the mud.
Exercise
Take one of your mixes, choose the 3 most important elements (e.g. vocal, kick, bass) and for each find what masks it the most. Solve it with one arrangement fix, one static EQ move and one dynamic one. Compare at equal loudness.
Related topics
“Slotting and interlocking”, “EQ by frequency zone”, “Psychoacoustics in mixing”, “Mixing the vocal in context”, “Static balance”.