Re: [LAD] vu-meter DSP

On Sat, Jul 27, 2013 at 06:32:33PM +0200, Robin Gareus wrote:
 
> How did you measure it? Did you plot the output of the filter for
> various input signals?

Yes. The VU was the easiest one. First get the overshoot right,
that's easy. Then plot the output of the DSP code, note the time
when it reaches 99%, adjust filter coefficient.

For the IEC I and II meters it's a lot more difficult. They are
specified by a drop rate (easy), and their response to various
burst test signals. For the real ones, the result is the combined
effect of a non-linear pseudo-peak detector, a non-linear mapping
to the meter scale, and the ballistics of the actual mechanical
meter (not always driven from a constant impedance, hence variable).
That is not something that will correspond to some readable equations.

The only way to get those right is to create some mathematical model
that you believe could do the right thing, then tune its parameters
by trial and error. If that fails try another model, until you get
well within the allowed error margins.

The most difficult one was the CCIR-468 response implemented in
jnoisemeter - that is a really weird one - the combination of
two interacting pseudo-peak detectors. There is an (unofficial)
equation for it which is rather useless and fills an A4 page.

> which leaves us with... Congrats Fons.

TNX ! But I'm not really surprised - I wrote the jmeters code
because I found *nothing* that really worked as it should have.
And as your tests have shown again, most don't even come close.

The videos are fun to watch...

BTW, while I have no problem with 'real' VUs, a bargraph
display - even if correct - looks somewhat hyperkinetic
to my taste... I wouldn't stand looking at it for too long.

Ciao,
 

-- 
FA
A world of exhaustive, reliable metadata would be an utopia.
It's also a pipe-dream, founded on self-delusion, nerd hubris
and hysterically inflated market opportunities. (Cory Doctorow)
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