Another question about VU

[Batz Goodfortune]

Y-ellow Y'all.
	While we're on the subject, and as embarrassing as it is for me to ask. I
need to know how to render a VU scale using an 8 bit A-D. In the simplest
possible terms. I was away the day they did math at school. I know it's log
20 something but I can't rap my brains round a ratio right now.

I'll explain the problem.

I need to build multiple bargraphs. The simplest way to do that is to use a
multi-channel A-D chip and a micro. The micros can drive LEDs directly and
multiplex them. So it would be a 2 or 3 chip solution. Small in size (very
important) and able to do all the nice bits like peak/average in software.

The way I imagined it would work is that there might be a look up table Or
at least a scale table, Where if a value was higher that a certain point it
would turn a LED on. Etc.

Now the problem is that In some cases this might be an array of the usual
10 LEDs. In other cases there are some 36 LED displays I can use. In yet
more cases I could use an LCD. On the LCD it could be showing the two main
channel outputs across the display in detail. In the other modes it could
be showing multiple channels in less detail vertically. So I'd like to have
some universal scale that divides the 256 step linear scale into the log 20
VU scale. Then I could apply this to any given set of bargraphs.

I just can't wrap my brain around it at the moment. And if you tell me,
you'd have to tell me in the simplest possible forms. "Do this, do that
then you get this..."

I know the proper VU (dB) scale is a ratio devised by nWatts into 600 ohms.
1mW thanks Tim. But how do you map that against a scale which could be
totally arbitrary and is actually measuring voltage?

I've been asking round without trying to embarrass myself in public like
this but I just had to bite the bullet in the end. <he says grimacing>

Thanks in advance.

Be absolutely Icebox.

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