D4 at a glance
All values assume twelve-tone equal temperament at the international standard pitch of A4 = 440 Hz. In that system every semitone has the same size - a frequency ratio of 2^(1/12) - so D4 is exactly 440 × 2^(-7/12) Hz. Under alternative references the note shifts with the reference: at A4 = 432 Hz, D4 becomes 288.33 Hz.
D in every octave
| Note | Frequency | MIDI | Piano key |
|---|---|---|---|
| D1 | 36.71 Hz | 26 | 6 |
| D2 | 73.42 Hz | 38 | 18 |
| D3 | 146.83 Hz | 50 | 30 |
| D4 ← | 293.66 Hz | 62 | 42 |
| D5 | 587.33 Hz | 74 | 54 |
| D6 | 1174.7 Hz | 86 | 66 |
| D7 | 2349.3 Hz | 98 | 78 |
Each octave doubles the frequency - the simplest relationship in music, and the reason notes an octave apart sound like “the same note, higher”.
Neighboring notes
One semitone down is C♯4 at 277.18 Hz; one semitone up is D♯4 at 311.13 Hz. Need a frequency between notes, or a different waveform? The tone generator plays anything from 20 Hz to 20 kHz; the note ↔ frequency converter does the math both directions, and the chromatic tuner listens to your instrument and shows the offset in cents.