- Joined Oct 16, 2011
In accepting as definition: dB=10log(Power-out/Power-in), we can derive an equivalent expression for voltage as vdB=20log(voltage-out/voltage-in). Indeed, it is always(?) seen that way. But, in order to derive the dB voltage expression from the dB power expression, one must(?) assume resistance remains constant. But in the case of amplifier gain, for example, there is no requirement that input and output impedances are the same. Is the expression invalidated in the case where input and output impedances don't remain the same?