Tool
Drone tone
Choose a note, an octave, and an A4 reference between 400 and 480 Hz. The page shows the frequency, then you can start a sine tone in this tab. The same drone is the one on the session bar, so you do not get two tones at once.
How the frequency is chosen
MIDI equals (octave + 1) × 12 plus the pitch class. Then frequency equals A4 times two to the power of (MIDI − 69) / 12. A4 is MIDI 69. That is the same formula as the note frequency calculator. The default A4 is 440 Hz.
The tone is a sine wave in Web Audio. It is a practice reference, not a studio oscillator and not a claim about concert pitch in the room.
Worked examples
Note A, octave 4, reference 440. The readout is 440.00 Hz. Can you match it on an open A string?
C4 is MIDI 60. At A4 = 440 Hz the frequency is about 261.63 Hz. Does that sit under a sung middle C?
The same A4 name with a 442 Hz reference is 442.00 Hz. Orchestras that tune high use a number near this.
Questions
Why is the range 400 to 480 Hz?
That window covers common concert references such as 432, 440, 442, and 444 without accepting an empty or zero field that would break the formula.
Will the drone continue on another page?
A full page load stops Web Audio. The session remembers the note and that you wanted a drone, so the bar can start it again.
Is this the tuner?
No. This page plays a tone. The chromatic tuner listens through the microphone.