Definition
A resonance is the tendency of a system (instrument body, room, filter, loudspeaker) to amplify energy around its own natural frequency f_0. Selectivity is expressed by the quality factor Q = f_0 / Δf, where Δf is the bandwidth at −3 dB. A high-Q resonance is narrow and decays slowly: the envelope time constant is τ = Q / (π · f_0) and the 60 dB decay time is T60 = 6.91 · τ. In enclosed spaces the main resonances are the axial modes: f_n = n · c / (2L), with c = 343 m/s and L the dimension of the room.
Masking is the psychoacoustic phenomenon by which one sound (the masker) reduces or eliminates the audibility of another sound (the masked).
- Simultaneous masking (in frequency): acts mainly within the same critical band; the equivalent rectangular bandwidth is ERB(f) = 24.7 · (4.37 · f / 1000 + 1) Hz, that is 35.5 Hz at 100 Hz, 132.6 Hz at 1 kHz, 456 Hz at 4 kHz. Masking extends further upward than downward (a loud low frequency masks higher frequencies) and this spread grows with the level of the masker.
- Temporal masking: a loud sound masks the soft sounds that follow it for 50–200 ms (post-masking) and, to a lesser extent, those that precede it by 5–20 ms (pre-masking).
- Spatial separation: two sources in different stereo positions mask each other less than two sources stacked in the center.
Parameters and units
- Resonance frequency: Hz.
- Q: 4–30 for instrument and room resonances; corrective cuts use Q 4–12.
- Gain of the resonant peak: 3–12 dB above the surrounding curve.
- Critical band: ERB in Hz or the Bark scale (24 critical bands between 20 Hz and 15.5 kHz).
- Masking times: pre 5–20 ms; post 50–200 ms.
Typical resonance zones in the mix:
| Source | Zone |
|---|---|
| Snare ring | 180–250 Hz and harmonics |
| Toms | fundamental 70–200 Hz |
| Acoustic guitar body | 90–120 Hz |
| Vocal nasality | 800 Hz–1.2 kHz |
| Harshness of vocals and distorted guitars | 2.5–4 kHz |
Musical function
Resonances give an instrument its character; in excess they make the sound boomy, nasal or harsh and make individual notes jump out. Masking is the main cause of lost definition in the mix: bass and kick in the same critical band, guitars and vocals between 1 and 4 kHz, pads and backing vocals in the mids. It is managed with complementary EQ (a cut on the secondary instrument where the main one has its identity), with dynamic EQ or sidechain compression, with panning, with the choice of octaves in the arrangement and with control of the tails (reverbs and delays that mask the following attacks).
Practical example
- Kick and bass: the kick fundamental at 55 Hz and the bass note A1 (55 Hz) fall in the same critical band (ERB at 55 Hz ≈ 30.6 Hz). Solution: dynamic EQ on the bass, bell at 55 Hz Q 2, range −4 dB, sidechain from the kick, release 80 ms; the bass gives up space only on the hits.
- Snare ring: resonance at 210 Hz with Q 30: τ = 30 / (π · 210) = 45 ms, T60 = 0.31 s. A −6 dB notch at 210 Hz with Q 8 reduces its tail without removing body.
- Listening room modes: in a room 4 m long the first axial mode falls at 42.9 Hz, the following ones at 85.8 and 128.6 Hz. At the listening position these frequencies can be boosted or cancelled by 10 dB or more: the judgment of the sub must be verified with the analyzer and on headphones.
Common mistakes
- Eliminating every resonance: the instrument loses its identity and becomes sterile.
- Evaluating masking in solo: it shows up only with all instruments playing.
- Raising both conflicting instruments in the same zone instead of cutting one.
- Using wide cuts for narrow resonances: the useful sound around them is removed too.
- Neglecting temporal masking: long reverbs and delays cover the attacks of the following notes.
- Correcting in the mix resonances of the listening room that do not exist in the file.
How to check it
- App analysis (layering): by comparing multiple files, the app indicates for each pair the Shared bands (masking), that is the bands in which both layers have their main energy, the Crowded bands (3 or more strong layers) and the Bands with no dominant layer. Shared bands call for complementary EQ, sidechain or a different octave.
- Energy per band: compare in the app the same band in two tracks that mask each other.
- EQ sweep: a narrow bell (Q 6–8) at +10 dB swept across the spectrum to find resonances; analyzer with peak hold and FFT ≥ 8192.
- Mute test: mute in turn the instrument suspected of masking and check how much the definition of the other improves.
Starting settings
| Parameter | Value | Why |
|---|---|---|
| Notch on a narrow resonance | −4/−8 dB, Q 6–12 | Reduces the tail without removing body. |
| Dynamic EQ bass/kick | −3/−6 dB at the fundamental, sidechain from the kick, release 60–120 ms | Gives the kick space only on the hits. |
| Complementary cut guitars/vocals | −2/−4 dB at 2–4 kHz, Q 1 | Frees the zone of vocal intelligibility. |
| Pan of conflicting instruments | ±30–70% | Spatial separation reduces masking. |
| Reverb pre-delay | 20–80 ms | Reduces the temporal masking of attacks. |
| FFT for resonances | ≥ 8192 samples, peak hold | Sufficient resolution for narrow peaks. |
Frequencies to watch
| Range | What to do |
|---|---|
| 40–100 Hz | Kick and bass: fundamentals in the same critical band; sidechain or dynamic EQ. |
| 180–250 Hz | Snare ring and tom body: narrow notches. |
| 800 Hz–1.2 kHz | Nasality of vocals and wind instruments. |
| 2–4 kHz | Masking between vocals, guitars and synths: complementary cuts. |
How to check the result
- Shared bands (masking) in the layering analysis: at most one per pair of main instruments, handled with EQ or sidechain.
- No Crowded band (3 or more strong layers) between 120 and 500 Hz.
- No narrow peak more than 6 dB above the average curve in the track's spectrum with peak hold.
- The vocal stays intelligible in the full mix at a low listening volume.