The rms opcode is really calculating it. The low-pass
filter has the same effect of applying a window to the
signal, and its cutoff freq is roughly equivalent to the
effect of changing the window size. It's a more efficient
way of doing the measurement.

Victor

>
> Hi all,
> I'm having a look at the way csound calculates RMS in the
> rms opcode, and it looks strange to me, I wonder if anyone
> can explain (in file Oops/ugens5.c line 948).
> RMS is here calculated as the square root of a low-pass
> filtered signal of the audio samples squared.
>
> My question is: Does this have the same effect as choosing
> a 'window', performing ordinary RMS calculations on the
> window, and then low-pass filtering these results?
>
> If not, is the rms opcode really calculating RMS?
>
> I remember pd calculates RMS in the windowed form (you
> have to choose a window size).
>
> Cheers,
> Andrés
>
>
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Thanks Victor. I thought it was something like that. Do you know whta
the relationship between the filter's cutoff frequency and window size,
or do you know where I could find this?

Thanks,
Andrés

Victor Lazzarini wrote:
> The rms opcode is really calculating it. The low-pass
> filter has the same effect of applying a window to the
> signal, and its cutoff freq is roughly equivalent to the
> effect of changing the window size. It's a more efficient
> way of doing the measurement.
>
> Victor
>
>   
>> Hi all,
>> I'm having a look at the way csound calculates RMS in the
>> rms opcode, and it looks strange to me, I wonder if anyone
>> can explain (in file Oops/ugens5.c line 948).
>> RMS is here calculated as the square root of a low-pass
>> filtered signal of the audio samples squared.
>>
>> My question is: Does this have the same effect as choosing
>> a 'window', performing ordinary RMS calculations on the
>> window, and then low-pass filtering these results?
>>
>> If not, is the rms opcode really calculating RMS?
>>
>> I remember pd calculates RMS in the windowed form (you
>> have to choose a window size).
>>
>> Cheers,
>> Andrés
>>
>>
>> ----------------------------------------------------------
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>> Csound-devel@lists.sourceforge.net
>> https://lists.sourceforge.net/lists/listinfo/csound-devel
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>
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I have to think a little, but overall, the lower the cuttoff frequency the
longer the averaging, the higher the cutoff, the  most responsive
the measurement is to quick changes in level.

At 12:58 13/12/2006, you wrote:
>Thanks Victor. I thought it was something like that. Do you know whta
>the relationship between the filter's cutoff frequency and window size,
>or do you know where I could find this?
>
>Thanks,
>Andrés
>
>Victor Lazzarini wrote:
> > The rms opcode is really calculating it. The low-pass
> > filter has the same effect of applying a window to the
> > signal, and its cutoff freq is roughly equivalent to the
> > effect of changing the window size. It's a more efficient
> > way of doing the measurement.
> >
> > Victor
> >
> >
> >> Hi all,
> >> I'm having a look at the way csound calculates RMS in the
> >> rms opcode, and it looks strange to me, I wonder if anyone
> >> can explain (in file Oops/ugens5.c line 948).
> >> RMS is here calculated as the square root of a low-pass
> >> filtered signal of the audio samples squared.
> >>
> >> My question is: Does this have the same effect as choosing
> >> a 'window', performing ordinary RMS calculations on the
> >> window, and then low-pass filtering these results?
> >>
> >> If not, is the rms opcode really calculating RMS?
> >>
> >> I remember pd calculates RMS in the windowed form (you
> >> have to choose a window size).
> >>
> >> Cheers,
> >> Andrés
> >>
> >>
> >> ----------------------------------------------------------
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> >>
> >
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Victor Lazzarini
Music Technology Laboratory
Music Department
National University of Ireland, Maynooth 


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