Appendix I
Working with Decibels
The decibel is a means to express logarithmic relationships across levels. For voltages, or sound pressure levels, the equation for a dB relationship is
where Vmeasured is the measured voltage and Vref is the reference voltage. There are several reference voltage values used in audio, shown in Table A1.1.
The most common reference for sound pressure level is 20 µN/m2 rms. Voltage and sound pressure level are analogous.
To use these, let’s calculate the voltage level for the specified input noise voltage of a microphone preamplifier having a rating of −127 dBm, a rather commonly seen number. The first thing we need ...
Get Sound for Film and Television, 3rd Edition now with the O’Reilly learning platform.
O’Reilly members experience books, live events, courses curated by job role, and more from O’Reilly and nearly 200 top publishers.
