Re: [Audacity-nyquist] Statistical analysis (and hello)

[Mikael <mr....@gm...>]

Hi George!

I have fiddled a bit with acoustics in audacity with some success and can
help out with the equivalent level. You can use the nyquist function snd-avg
to get it like this:

(setq sl (snd-length s 999999999999))
(setq calibration 97)
(+ calibration (* 0.5 (linear-to-db (snd-maxsamp (snd-avg (mult s s) sl sl
OP-AVERAGE) ))))

Paste this into the Effect -> Nyquist prompt, and you'll get the equivalent
level in dB of what ever mono audio you selected. Of course it is
uncalibrated, that's why I have the calibration variable if you would like
to set it. Using 97 like I do seems to give 94 dB for a 1000 Hz tone with
amplitude 1.0.

Note that it is the equivalent level without A-weighting, to get that you
need to filter with an A-filter first (se the post by Edgar you mention).
Watch out for clipping when filtering, I believe audacity clips any sample
above 1.0...

I would guess that L10 and L90 are more diffcult, I think you need to
calculate the histogram to get it. Please mail any success to this list.

Mikael Ogren

PS I use snd-maxsamp to extract the single sample from the previous step, I
guess there is a more elegant way but I couldn't find it. DS

>
>
> On 1/12/07, Alex S. Brown, PMP <ale...@al...> wrote:
> >
> > I did a silence-detection plug-in which is now included in the regular
> > Audacity distribution. That required me to look at some very basic noise
> > detection issues. I did not have to do the statistical analysis, because
> >
> > I just looked at areas of the signal that exceeded or fell below a set
> > threshold.
> >
> > You could look at my plug-in for help. I found one of the hardest parts
> > of writing it was being careful not to accumulate all the samples in
> > memory. If you do, then your memory use quickly skyrockets for anything
> > more than a very short sound wave.
> >
> > Your first step should be to look at the built-in functions to
> > manipulate the signal. If you can find a way to reduce the number of
> > samples you have to read, you will get a result much more quickly.
> >
> > If you need specific advice, let us know more about the math of your
> > calculation and how it is typically done, and we might be able to guide
> > you towards some useful built-in functions or programming models.
> >
> > --Alex
> >
> > George Jenner wrote:
> > > Hello,
> > >
> > > I was just searching the archives to see if I could do some
> > > statistical analysis of recordings.  I see Edgar recently published an
> >
> > > A-weighting filter and I've succesfully runi it as my first plug in.
> > > (Sorry I've only just joined the list so I only know you by the
> > > archives).
> > >
> > > At work I'm using audacity to measure noise levels, so I wonder if
> > > this has been done before.  I'd like to determine L10, L90 and Leq of
> > > a sample.  For those of you whose jobs are more interesting than mine,
> > > L10 is the level which is exceeded by 10% of all samples.
> > >
> > > Has this been done by anyone?  Lisp is a foreign language to me so
> > > I'll need some time to get used to it.
> > >
> > > Thanks for any help,
> > > George
> >
> > --
> > Alex S. Brown, PMP
> > ale...@al...
> > http://www.alexsbrown.com - Free PM Articles
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> >
> >
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