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Subject: Re: [patch] volume peak meter in wps
From: Jack Peel (jhp_at_cypress.com)
Date: 2002-09-19


Philipp Pertermann wrote:

> From: "Jack Peel" <jhp_at_cypress.com>
> > > > Also could you put "clip" "lights" on it so that if
> the MP3 goes
> > > > to full scale it shows a different symbol and it hangs
> out longer
> > > > so that we know if the MP3 itself is clipping ?
> > >
> > > Yes, I could.
>
> Now I fiddled a bit with that. I don't like it much because
> it is incredibly unreliable. The 'quasi peak detector' of
> the mas is very 'quasi' but not so much a 'peak detector'.
> If we don't read the peak value exactly when it happens we
> miss it. I now installed a polling thread that reads out the
> mas quite often but still many peaks remain undetected. So
> the whole peak meter is a toy and not a reliable measuring
> tool.
>
> Phil

Well, in theory the human ear cannot hear a clip if it is only a few
samples long, so we would only be interested in seeing a "clip" if
it were several samples long. But after thinking about it, seeing the
peak level indicators at full scale will tell you enough. And the user
can set how long they stick around already. It would be nice however
to do the "set until reset" function on the peak meters :) The only
problem is how do we easily reset them without having to go through
3 levels of menus :) I guess you could just add it to one of the F2 or
F3
key functions from the wps screen.

Any luck with the linear to log conversion ?

I was thinking about the lookup table issue, and you could probably drop

a couple of bits off of the number to reduce the size of the table and
we
would probably never be able to tell. Since it is a 15 bit number you
could
probably drop 5 bits and I would never be able to tell, maybe even 7
bits.
Another Idea is that we only really care about the accuracy when we are
close to the top so you might be able to "shape" the table to have
more accuracy at the top. The Idea is that -1 dB and -2 dB are VERY
difference, however -41 dB and -42 dB are not. It may however be
too much coding trouble to handle the shaped table.

Just some Ideas :)

Jack



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