On Fri, 10 Mar 2000, andy howard wrote:

> Date: Fri, 10 Mar 2000 01:19:11 -0000
> From: andy howard <musica@UKONLINE.CO.UK>
> Reply-To: andy howard <music@soon.com>
> To: PICLIST@MITVMA.MIT.EDU
> Subject: Re: VU meter
>
> When calculating power ratios the formula is 10*log(x1/x2) where x1 and
> x2 are power measurements in e.g. watts. For voltage (or current) ratios
> you use 20*log(x1/x2) where x1 and x2 are voltages (or currents).
>
> If you double the voltage across a given load you will quadruple the
> power dissipated since power is proportional to the square of the
> voltage (p=v2/r).  Thus 6dB is a doubling of voltage but 3dB is doubling
> of power.
>
> Thus is the mighty Ohm's Law preserved.
All kneel.

OK, OK, it's all coming back like a bad dream. So (segue back to the
original topic) each bit of a A/D sample represents 2 x voltage = 4 x
power = +6dB. But (I think) I want +3dB increments for my bargraph. So
what I need to do is magically multiply the sample by sqrt(2)/2, yielding
sqrt(2) x voltage = 2 x power = +3db per bit. Does this seem right?

-- Rich