How to use it
- Choose whether to find the beat frequency or the second tone.
- Enter the first tone in Hz, for example the reference pitch A 440.
- Enter the second tone, or the number of beats you count per second.
- Read the beat frequency, the beat period, beats per minute, the perceived pitch and the interval in cents.
Formulas
- Beat frequency: f_beat = |f₁ − f₂|
- Beat period: T = 1 ÷ f_beat
- Perceived pitch: (f₁ + f₂) ÷ 2
- Interval in cents: 1200 × log₂(f₂ ÷ f₁)
- From a counted beat rate: f₂ = f₁ − f_beat or f₁ + f_beat
Worked example
A tuning fork at 440 Hz and a string at 444 Hz: f_beat = 444 − 440 = 4 Hz, a swell every 0.25 s, 240 a minute. You hear 442 Hz, and the string is 15.67 cents sharp.
A string at 438.5 Hz against the same fork: 1.5 beats a second, one every 0.6667 s, and the string is 5.91 cents flat (−5.91 ¢).
Tips
- Count beats over several seconds. Ten beats in five seconds is 2 Hz, easier than timing one.
- Slow beats are close tuning. At A 440, 1 beat a second is about 4 cents.
- Beats need similar loudness. If one tone is much louder the swells become shallow and hard to hear.