Sound Converter

This converter handles sound level units (the decibel, bel and neper) used to express ratios of sound intensity or signal level on a logarithmic scale.

Logarithmic units are used because human hearing spans an enormous range of intensities.

A decibel is not a quantity of sound but a ratio expressed on a logarithmic scale, and the arithmetic behaves accordingly. Adding 10 dB multiplies power by ten. Adding 20 dB multiplies it by a hundred. Adding 3 dB doubles it.

Perception does not follow the same curve. A tenfold increase in power (that same 10 dB) is heard as roughly a doubling of loudness, which is exactly why the scale exists: it compresses a range of intensities spanning many orders of magnitude into numbers a person can work with.

• Two identical sources together produce 3 dB more than one, not double the decibel figure.
• A 60 dB conversation and an 80 dB street are not related by a third: the street carries a hundred times the power.
• One bel is ten decibels; the decibel is used almost universally because the bel is inconveniently large.

Because the decibel expresses a ratio, a value in decibels only means something once you know what it is a ratio to. That reference is carried in a suffix, and the suffixes are not interchangeable.

dB SPL is referenced to the threshold of human hearing and is what sound level meters report. dBA applies a weighting curve that de-emphasises frequencies the ear is less sensitive to, which is why it is used for noise regulations. In audio equipment dBu and dBV reference specific voltages, and in radio dBm references one milliwatt.

• A bare "dB" figure with no suffix is ambiguous unless the context makes the reference obvious.
• Nepers express the same idea using natural logarithms rather than base ten, and appear in engineering rather than acoustics. One neper is about 8.686 dB.
• Negative decibel values are perfectly ordinary; they simply mean the measured quantity is below the reference.