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used since a doubling of voltage is a change of 6dB while a doubling of power is a change of 3dB. For the most part we will be using the 20 log version since acoustic pressure (dB SPL) and voltage are the primary drivers of our decision-making. Figure 1.10 provides a reference chart to relate the ratios of values to their decibel equivalents.
Here is a handy tip for Microsoft Excel users. Figure 1.11 shows the formula format for letting Excel do the log cal- culations for us.
The Electronic Decibel: dBV and dBu
Electronic transmission utilizes the decibel scale to charac- terize the voltage levels. The decibel scale is preferred by operators over the linear scale for its relative ease of expres- sion. Expressed linearly we would find ourselves refer- ring to the signal in microvolts, millivolts and volts with various sets of number values and ranges. Such scaling makes it difficult to track a variable signal such as music. If we wanted to double the signal level we would have to first know the voltage of the original signal and then compute its doubling. With dynamically changing signals such as music, the level at any moment is in flux, making such calculations impractical. The decibel scale provides a relative change value independent of the absolute value. Hence the desire to double the level can be achieved by a
There are two types of log formulas applicable in audio:
Power-related equations use the 10 log version, while pressure (SPL) and voltage related equations use the 20 log version. It is important that the proper formula be
