We use two different forms of decibels in audio: the decibel scale which measures sound pressure level relative to human hearing, and units that measure either power or relative voltage level. The decibel (dB) scale sets zero as the lowest sound pressure level at which most people can hear a sound. Electrical signal strength is measured in units like the dBm, with “m” being short for milliwatt. Relative voltage level is measured in units like dBu and dBV. The “u” in dBu stands for unloaded.
All of us have probably at least heard of the decibel scale, but do you know how it originated? That is the subject of today’s post.
We use a logarithmic rather than a decimal scale to measure amplitude to make the numbers more manageable. The original unit that was developed was called the bel, after Alexander Graham Bell. This number proved to be too large to use with sound, so engineers eliminated the last zero and named the new unit the decibel, or one tenth of a bel. The decibel scale is measured from an arbitrary point called 0 dB. This does not mean, however, that a sound that measures 0 dB has zero amplitude.
The human ear is able to detect sounds that lie roughly between the frequency range of 20 Hz and 22,000 Hz. Hz is the abbreviation for Hertz, named for the German physicist Heinrich Hertz. Specifically, Hz is a measure of the number of cycles per second, or oscillations, the atmosphere is disturbed by the phenomenon we call sound. Most musical instruments are tuned to the A above middle C, which vibrates at 440 Hz.