Ralf Kuchenhart wrote: (or schrieb)
>The formular for sound power level is 10(dB)* log (I/Io), but the formular
for
>sound pressure is 20(dB)*log (p/p0). If you regard the (electrical) power
you
>need in your amps and to drive the speakers, your formular is absolutely
right,
>Ian, but if you regard the electric level you record from the microphone,
you
>have to use the formular for the sound pressure. Therefore, the step of 1
bit in
>the PCM code is always 6(.02) dB, not 3(.01) dB.
When you say electric level Ralf, you need to be a little more specific.
The voltage level follows the 20log... formula, but if you measure the power
being delivered by the microphone to the preamp, it still follows the
10log... formula, as any electrical power ratio always will.
When talking PCM code, you are always referring to digital representations
of voltage, not power. That is why every bit adds 6.02dB of dynamic range.
By doubling the available voltage range (adding 1 bit of resolution) we are
quadrupling the available power range, and this solves in the 10log...
formula.
-cb
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