The actual definition
Resonance occurs when a driving frequency matches the natural frequency of a system. At that rate the system responds far more strongly than at any other, because energy delivered on each cycle accumulates rather than dissipating.
This is why a badly sized room has no good place to stand, why a wine glass shatters when a sustained note matches its rate, and why a cello sounds like a cello. Same mechanism, wildly different consequences.
Everything resonates
It is tempting to treat resonance as something unusual. It is not. It is the default behaviour of physical systems driven periodically, which means everything in a mix is resonating all the time.
| System | Natural rate | Audible effect |
|---|---|---|
| Room | Low, broad | Bass build-up or a hole at one frequency |
| Guitar body | Mid, shaped by the air cavity | The warmth of an acoustic instrument |
| Voice | Formant regions in the vocal tract | Why one vowel sounds unlike another |
| Microphone body | Mechanical resonance | A colouration that sounds like that mic |
Once you accept that resonance is everywhere, the useful question becomes which resonances you can control. Instruments and voices are mostly fixed. The room is usually fixed. Filters and EQ are where you have leverage.
Sympathetic resonance
When one vibrating object sets another into motion without direct contact, that is sympathetic resonance. A guitarist playing near an open piano lid will set the strings moving. A cymbal in a room will pick up the kick drum.
In mixing it is the reason bleed matters, and the reason an unprocessed acoustic piano sample can sit oddly in a dense arrangement. The instrument recorded more than the note you hit.
Resonance and EQ
A narrow boost centred on a resonant peak does not add resonance, it adds gain at a frequency where resonance already concentrated energy. That is why boosting a room mode makes the boom worse rather than fixing it, and why cutting is almost always the better move.
High-pass filters and clean mixes covers the subtractive approach. The principle generalises: remove the problem before adding anything.
Reference, room, and what you cannot fix
Changing the tuning reference changes where a mix sits against the resonances of every room it will be played in. That is a real effect and one of the less discussed consequences of retuning.
432Hz MASTER and RASTA 528Hz shift the whole mix, so the relationship between your music and any given room changes. Whether that helps depends on the room.
Sharpness and why some resonances hurt
Not all resonances are equally troublesome, and the reason is often called Q, for quality factor. A high-Q resonance is narrow and rings for a long time. A low-Q resonance is broad and settles quickly.
| Resonance | Q | Audible effect | What to do |
|---|---|---|---|
| Room boom | Low | Broad, sustained low build-up | Cut with a high-pass or a wide cut |
| Boxy resonance | Medium | Narrow lump around 200 to 400Hz | Cut the narrow peak |
| Feedback howl | Very high | A note that will not stop | Break the loop, do not EQ it |
| Boom mic resonance | High | Honky nasal quality | Cut the peak, or move the mic |
| Snare body | High | Ringing that masks the mix | Cut the specific ring frequency |
The practical rule follows from the physics: narrow problems want narrow cuts, and broad problems want broadband removal. Using the wrong tool is why some room problems survive several attempts at EQ and then vanish on the first high-pass.
How to hear resonance
Resonance is easy to hear once you know what to listen for, and hard to hear if you do not, because it sounds like the source rather than like an effect.
- Solo the source and listen for a pitch that survives long after the note has stopped.
- Sweep a narrow boost slowly across the low end and stop where the sound grows most with very little boost.
- In a room, move through positions. A frequency that is fine at one spot may be three decibels loud two metres away.
- Check a mono fold-down, since a narrow resonance often sits hard on one side.
The swept-boost method is the fastest diagnostic available. If a small amount of boost produces a large change in tone, you have found a resonance rather than a broad balance issue.
The bottom line
Resonance is the most overextended word in discussions about tuning. It is also one of the best-established pieces of physics in audio, and the two facts are not in conflict. What resonance describes is why some frequencies build up in a system and others cancel, which is exactly what a room does to your mix.
Hear a room respond
432Hz MASTER and RASTA 528Hz move a whole mix to a new reference, changing where it sits against resonant surfaces.
Frequently asked questions
What is resonance?
When a driving frequency matches the natural frequency of a system, that system responds far more strongly than to any other input. Energy accumulates rather than dissipating.
Does every object have a resonant frequency?
Every physical system has one or more natural rates at which it responds strongly. A wine glass, a guitar string, a room and a human ribcage all have them.
Is resonance the same as the universe resonating at 432Hz?
No. Resonance describes a system responding to a matching input. The claim that the universe itself resonates at 432Hz is an interpretive framing, not a measurement.
How does resonance affect mixing?
Every room has resonant frequencies that colour what you hear, and every instrument has resonances that colour what it produces. EQ can shift a resonance but it cannot move the room.