#Define decibel full

Measurements relative to 10 -12 W/m 2 which is approximately the level of human hearing in air.ĭB Sound Power level. The common decibel units used in acoustics are: dB(SPL)

#Define decibel full

Note that since the most common usage of the decibel unit is for sound pressure level measurements it is often abbreviated to just dB rather than the full dB(SPL). This is about the limit of sensitivity of the human ear. Furthermore, since sound power is proportional to the pressure squared then this ratio is approximately 1 trillion.įor sound pressure levels, the reference level is usually chosen as 20 micro-pascals ( ), or 2×10 -5 Pa. The decibel is particularly useful for acoustic measurements since for humans the ratio of the loudest sound pressure level to the quietest level that can be detected is of the order of 1 million. This may be to compare two sound sources or to quantify the sound level perceived by the human ear. The decibel is commonly used in acoustics to quantify sound levels relative to a reference. The dB unit is often qualified by a suffix which indicates the reference quantity used, some examples are provided in the following section. That is, if a particular reference value is known then the exact measurement value can be recovered from one of the equations shown above. Like all logarithmic quantities it is possible to multiply or divide dB values by simple addition or subtraction.ĭecibel measurements are always relative to given reference levels and can therefore be treated as absolute measurements. The logarithmic scale approximately matches the human perception of both sound and light. Since the decibel is a logarithmic quantity it is especially good at representing values that range from very small to very large numbers. When considering amplitude levels, the power is usually estimated to be proportional to the square of the amplitude and so the following can be used: The mathematical definition is the ratio ( ) of a power value ( ) to a reference power level ( ) and in decibels is given by: DefinitionĪ decibel is used for the measurement of power or intensity. Since it expresses a ratio of two quantities having the same units, it is a dimensionless unit. The decibel is a logarithmic unit of measurement that expresses the magnitude of a physical quantity relative to a reference level. This applies to Prosig’s P8000 range of data acquisition hardware where the noise floor, dynamic range and resolution are all specified in terms of dB. One particular use of dB is to quantify the dynamic range and accuracy of an analogue to digital conversion system. However, as will be explained in this article, it is also useful for a wide variety of measurements in other fields such as electronics and communications. Its most common use is in the field of acoustics where it is used to quantify sound levels. Most engineers are probably familiar with or have come across the decibel or dB as a unit of measurement.