A Note on Pitch and Frequency

Generally, harmonic sounds are those for which we hear a pitch (you can hum them).

Scientific pitch notation combines a note name with an octave number:

• C4 is middle C;
• A4 or A440 (440 Hz) is in the same octave (above) middle C and is often used as a reference tone.

Recall, in equal-tempered tuning, there are 12 evenly spaced tones (semitones) in an octave,

• The frequency $n$ semitones above/below A440 is
  $$440 \times 2^{\pm n/12}$$    Hz$$.$$