MusicReasonProduction, Synthesis, and Audio Math
What note is this cutoff frequency near?
Enter a filter cutoff frequency. This tool maps it to the nearest equal-tempered note for orientation, the same way a synthesizer's filter knob sometimes shows a note name. A filter cutoff is not itself a perceived pitch, and this mapping does not imply the setting will be audible in isolation.
Answer
Understand
A low-pass or high-pass filter's cutoff frequency marks where the filter begins attenuating content, not a pitch someone hears ringing out. Naming its nearest note is still a genuinely useful orientation tool, since musicians often think in note names, but the actual audible effect of a cutoff setting depends heavily on the filter's slope and resonance, neither of which this mapping addresses.
Worked examples
A cutoff of 440 Hz maps to A4 exactly, zero cents away. Doubling that cutoff to 880 Hz maps to A5, exactly one octave higher, since doubling frequency always raises pitch by exactly 12 semitones regardless of the starting note.
Method and limitations
The cutoff frequency converts to an exact MIDI note number using the same locked frequency-to-note formula Frequency to Note uses, rounds to the nearest integer note, and reports the signed cents remainder. This tool never implies the filter cutoff has a perceived pitch of its own or that the setting will be audible on any given source material; it only offers a note-name orientation for a numeric frequency value.
Two cutoffs that map to the same note name are not necessarily musically interchangeable: the cents remainder shows how far off an exact note the cutoff actually sits, and a filter set right between two notes will show a remainder near 50 cents either way, a genuinely ambiguous case this tool reports honestly rather than forcing toward whichever note happens to be nominally closer.
Changing the A4 reference shifts every mapped note name slightly, since it redefines where the whole 12-TET grid sits relative to absolute frequency; a cutoff mapped to A4 exactly under a 440 Hz reference will show a small nonzero cents deviation under a 442 Hz reference instead, even though the cutoff frequency itself never changed. This is the same reference-pitch sensitivity Reference Pitch and Cents makes explicit for tuning work generally.