Audio decibels

It should also be noted that in audio, many operations are calibrated in decibels. This implies the need for a logarithm (base 10). If possible, such computations should be avoided since the Taylor series calculation method is multiplier intensive. Short cuts, such as direct table lookup are preferable when possible. 

The simplest definition of a level measurement is the alternating current (AC) amplitude at a particular place in the audio system. In contrast to dhect current measurements, however, there are many ways of specifying AC voltage. The most common methods are average, root-mean-square (RMS), and peak response. Strictly speaking, the term level refers to a logarithmic, or decibel, measurement. However, common parlance employs the term for an AC amplitude measurement, and that convention will be followed in this chapter. 

Measurements in audio work are usually expressed in decibels. Audio signals span a wide range of level. The sound pressure of a live concert band performance may be one miUion times that of rustling leaves. This range is too wide to be accommodated on a linear scale. The logarithmic scale of the decibel compresses this... 

Audio engineers often express the decibel value of a signal relative to some standard reference instead of another signal. The reference for decibel measurements maybe predefined as a power level, as in decibels referenced to 1 mW (dBm), or it may be a voltage reference, as in decibels referenced to 1 V (dBV). When measuring dBm or any power-based decibel value, the reference impedance must be specified or understood. Often it is desirable to specify levels in terms of a reference transmission level somewhere in the system under test. These measurements are designated dBr, where the reference point or level must be separately conveyed. 

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