Re: [PD] how does env~ work?

[Orm Finnendahl]

Am Donnerstag, den 23. März 2017 um 17:00:14 Uhr (-0300) schrieb Alexandre 
Torres Porres:
> > the hanning envelope itself actually goes from 0 to "2" and not from 0 to
> > 1, so I assume the compensation is done right there...
> >
> 
> tested with an envelope going from 0 to 1 and lost about 3.0103 dB ;)

You're almost there: If you average the values in a rectangular window
with the amplitude 1 you will get 1, the same value results if
averaging the values of a Hanning window with amplitude 2 (you can
check that by building the definite integral of the Hanning function
cos(x-pi)+1 in the interval [0..6.28] and divide that by the width of
the interval (6.28)).

If you use a Hanning window of amplitude 1, you'll get 0.5 as the
average. As the windowing is applied to the squared values, after
calculating the root (for obtaining the "R"MS), you'll end up with
sqrt(0.5) = 0.707 of the "real" RMS value and that equals to -3.0103
dB.

In short: Using a Hanning window with amplitude 2 on the squared
values will compensate the loss of the resulting mean value introduced
by the windowing function. The result is a compensated RMS value with
an emphasis on the center of the analysis window. In this use case the
windowing results in smoothing the irregularities you observed when
using rectangular windows.

--
Orm

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Re: [PD] how does env~ work?

[Alexandre Torres Porres]

easy, I do at least know that much about what squaring is ;)

2017-03-23 19:27 GMT-03:00 Christof Ressi :

>
> F(1) (= the sum after a full period) is 0.5. That's the reason why the
> Hanning window in this case is twice as large to bring the sum to 1.
> weighting a constant(!) signal with such a Hanning window will yield the
> same sum as with a non-weighted signal.
>

thanks for trying again,I figured something like that happened, but I still
can't get my head around the math ;) - I'll just be happy knowing it works
for some reason... haha
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Re: [PD] how does env~ work?

[Christof Ressi]

> sorry, I guess I didn't get most of what you said :/ kinda over my head...
 
no worries. just an awkward attempt from my side to explain code with words :-D.
 

> actually, also, the envelope is applied to the squares of the amplitudes... 
> and this gets me completely lost now on what it means mathematically
 
https://en.wikipedia.org/wiki/Root_mean_square
 
in short, RMS means you square each sample, sum them, divide the sum by the 
number of samples and then take the square root. in case you're wondering where 
the square root is, it is in powtodb(). compare rmstodb() and powtodb() to see 
the difference. rmstodb() expects an rms value (the square root already taken) 
while powtodb() will take the square root for you (and luckily, log(sqrt(x) is 
simply log(x)/2).
 

> the hanning envelope itself actually goes from 0 to "2" and not from 0 to 1, 
> so I assume the compensation is done right there... 
 
that's a good observation! 

the integral (= running sum) of 
f(x) = 0.5 - cos(2pi*x)*0.5 (= Hanning window within range 0-1) 
is 
F(x) = x*0.5 - sin(2pi*x)/4pi 

F(1) (= the sum after a full period) is 0.5. That's the reason why the Hanning 
window in this case is twice as large to bring the sum to 1. weighting a 
constant(!) signal with such a Hanning window will yield the same sum as with a 
non-weighted signal.

Christof
 


Gesendet: Donnerstag, 23. März 2017 um 21:11 Uhr
Von: "Alexandre Torres Porres" <por...@gmail.com>
An: "pd-list@lists.iem.at" <pd-list@lists.iem.at>
Betreff: Re: [PD] how does env~ work?

actually, also, the envelope is applied to the squares of the amplitudes... and 
this gets me completely lost now on what it means mathematically
 
2017-03-23 17:00 GMT-03:00 Alexandre Torres Porres 
<por...@gmail.com[mailto:por...@gmail.com]>:
 
 

2017-03-23 16:53 GMT-03:00 Alexandre Torres Porres 
<por...@gmail.com[mailto:por...@gmail.com]>:
 
 
2017-03-23 16:45 GMT-03:00 Alexandre Torres Porres 
<por...@gmail.com[mailto:por...@gmail.com]>:

 
and as I see it, it's just applying a hanning envelope into the input and 
NOTHING more, right?
 
the hanning envelope itself actually goes from 0 to "2" and not from 0 to 1, so 
I assume the compensation is done right there... 
 
tested with an envelope going from 0 to 1 and lost about 3.0103 dB 
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Re: [PD] how does env~ work?

[Martin Peach]

On Thu, Mar 23, 2017 at 4:11 PM, Alexandre Torres Porres 
wrote:

> actually, also, the envelope is applied to the squares of the
> amplitudes... and this gets me completely lost now on what it means
> mathematically
>
>
It means that negative signals will count the same as positive ones.

Martin
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Re: [PD] how does env~ work?

[Alexandre Torres Porres]

actually, also, the envelope is applied to the squares of the amplitudes...
and this gets me completely lost now on what it means mathematically

2017-03-23 17:00 GMT-03:00 Alexandre Torres Porres :

>
>
> 2017-03-23 16:53 GMT-03:00 Alexandre Torres Porres :
>
>>
>>
>> 2017-03-23 16:45 GMT-03:00 Alexandre Torres Porres :
>>
>>>
>>> and as I see it, it's just applying a hanning envelope into the input
>>> and NOTHING more, right?
>>>
>>
>> the hanning envelope itself actually goes from 0 to "2" and not from 0 to
>> 1, so I assume the compensation is done right there...
>>
>
> tested with an envelope going from 0 to 1 and lost about 3.0103 dB ;)
>
>
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Re: [PD] how does env~ work?

[Alexandre Torres Porres]

2017-03-23 16:53 GMT-03:00 Alexandre Torres Porres :

>
>
> 2017-03-23 16:45 GMT-03:00 Alexandre Torres Porres :
>
>>
>> and as I see it, it's just applying a hanning envelope into the input and
>> NOTHING more, right?
>>
>
> the hanning envelope itself actually goes from 0 to "2" and not from 0 to
> 1, so I assume the compensation is done right there...
>

tested with an envelope going from 0 to 1 and lost about 3.0103 dB ;)
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Re: [PD] how does env~ work?

[Alexandre Torres Porres]

2017-03-23 16:45 GMT-03:00 Alexandre Torres Porres :

>
> and as I see it, it's just applying a hanning envelope into the input and
> NOTHING more, right?
>

the hanning envelope itself actually goes from 0 to "2" and not from 0 to
1, so I assume the compensation is done right there...
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Re: [PD] how does env~ work?

[Alexandre Torres Porres]

2017-03-23 6:54 GMT-03:00 Orm Finnendahl
>
> In the object's new method, the object allocates a buffer ("buf") and
> writes the Hanning function with RMS compensation (the two nested
> divisions by npoints) into it.
>

ok, I get "buf" is a hann window with very small values (which depend on
npoints, the greater, the smaller) - so by dividing it by the number of
points, it's already doing the 'mean' value... that's what you mean by "RMS
compensated"?

I don't get what 'hp' is (x->x_buf + count)

all values (which depend on npoints, the greater, the smaller).

then I get that the square sum is normalized by being multiplied to 'hp'...

So, Basically, if I want to remove the 'hann normalization', I just take
'hp' out and divide it by npoints.

I tried it, and what I get is a more deviated value.

and as I see it, it's just applying a hanning envelope into the input and
NOTHING more, right?

It is not really compensating in any way, either with overlaping, or
multiplying the result for normalizing it, huh?

This was my original question, if it was compensated somehow, but it seems
not.

cheers
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Re: [PD] how does env~ work?

[Christof Ressi]

> (and feel like the overlap affects only the output rate)

Exactly! That's what i meant.

> 2017-03-23 10:59 

> Gesendet: Donnerstag, 23. März 2017 um 15:12 Uhr
> Von: "Alexandre Torres Porres" <por...@gmail.com>
> An: "Christof Ressi" <christof.re...@gmx.at>
> Cc: "pd-list@lists.iem.at" <pd-list@lists.iem.at>
> Betreff: Re: Re: [PD] how does env~ work?
>
> I do realize the windowing makes the result more accurate and stable,
> somehow... (and feel like the overlap affects only the output rate)
> 
> 2017-03-23 10:59 GMT-03:00 Alexandre Torres Porres <por...@gmail.com>:
> 
> >
> >
> > 2017-03-23 10:58 GMT-03:00 Alexandre Torres Porres <por...@gmail.com>:
> >
> >> how does overlap affect the rms value? If I use an overlap of 32 I see no
> >> difference, except the output rate.
> >>
> >
> > this is comparing an overlap of 32 to an overlap of "1" (no overlaps), and
> > a window size of 8192 (256 being the hop size) - the input is a sinusoid
> >
>

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Re: [PD] how does env~ work?

[Orm Finnendahl]

Am Donnerstag, den 23. März 2017 um 10:59:16 Uhr (-0300) schrieb Alexandre 
Torres Porres:
>
> the input is a sinusoid

That's the problem: If the size of the analysis window is sufficiently
large compared to the frequency of a static sinusoid You can't really
expect any difference in the rms values if the window gets shifted. As
stated before, no overlap-add is performed.

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Re: [PD] how does env~ work?

[Alexandre Torres Porres]

I do realize the windowing makes the result more accurate and stable,
somehow... (and feel like the overlap affects only the output rate)

2017-03-23 10:59 GMT-03:00 Alexandre Torres Porres :

>
>
> 2017-03-23 10:58 GMT-03:00 Alexandre Torres Porres :
>
>> how does overlap affect the rms value? If I use an overlap of 32 I see no
>> difference, except the output rate.
>>
>
> this is comparing an overlap of 32 to an overlap of "1" (no overlaps), and
> a window size of 8192 (256 being the hop size) - the input is a sinusoid
>
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Re: [PD] how does env~ work?

[Alexandre Torres Porres]

2017-03-23 10:58 GMT-03:00 Alexandre Torres Porres :

> how does overlap affect the rms value? If I use an overlap of 32 I see no
> difference, except the output rate.
>

this is comparing an overlap of 32 to an overlap of "1" (no overlaps), and
a window size of 8192 (256 being the hop size) - the input is a sinusoid
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Re: [PD] how does env~ work?

[Alexandre Torres Porres]

how does overlap affect the rms value? If I use an overlap of 32 I see no
difference, except the output rate.

2017-03-23 8:07 GMT-03:00 Christof Ressi <christof.re...@gmx.at>:

> some additions:
>
> the object maintains a summing buffer where it writes the current sum of
> the different analysis windows (the number of windows depends on the hop
> size), starting with the most recent one.
>
> what happens in the loop is that it takes n input samples, squares them,
> multiplies it with a section of the hanning windows depending on the
> current phase and adds the sum to the first element of the summing buffer.
> this is repeated for the number of overlaps, but the pointer into the
> hanning window gets incremented based on the phase difference (= hop size)
> and the result is now added to the *next* element in the summing buffer etc.
>
> once the sum of a complete analysis window has been calculated (this takes
> 16 DSP ticks when your block size is 64 and the [env~] window size is
> 1024), the elements of the summing buffer are shifted one element to the
> front, the front (= sum of the most recent window) itself gets popped and
> passed to the outlet (where it is converted from power to decibels).
>
> the powtodb function takes care of taking the square root of the sum but
> it's done in the logarithmic domain where it's just a division by two.
>
> with smaller hop sizes you basically just get more frequent updates while
> maintaining a larger window size but with more CPU cost.
>
> this is at least how I understood the code.
>
> > Gesendet: Donnerstag, 23. März 2017 um 10:54 Uhr
> > Von: "Orm Finnendahl" <orm.finnend...@selma.hfmdk-frankfurt.de>
> > An: pd-list@lists.iem.at
> > Betreff: Re: [PD] how does env~ work?
> >
> > Am Donnerstag, den 23. März 2017 um 01:34:58 Uhr (-0300) schrieb
> > Alexandre Torres Porres:
> > > howdy, help file says "The analysis is "Hanning" (raised cosine)
> windowed."
> > >
> > > how does that work? I tried looking at the code and got no clue...
> >
> > In the object's new method, the object allocates a buffer ("buf") and
> > writes the Hanning function with RMS compensation (the two nested
> > divisions by npoints) into it.
> >
> > >
> > > I assume it's not just passing the input through a hanning window, and
> one
> > > way or another,
> >
> > That's exactly what it does. The Hanning window emphasizes the middle
> > of the analysis window and by adjusting the hop size in the second
> > argument of env~ you can fine tune the results.
> >
> > --
> > Orm
> >
> > ___
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> >
>
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Re: [PD] how does env~ work?

[Christof Ressi]

some additions:

the object maintains a summing buffer where it writes the current sum of the 
different analysis windows (the number of windows depends on the hop size), 
starting with the most recent one. 

what happens in the loop is that it takes n input samples, squares them, 
multiplies it with a section of the hanning windows depending on the current 
phase and adds the sum to the first element of the summing buffer. this is 
repeated for the number of overlaps, but the pointer into the hanning window 
gets incremented based on the phase difference (= hop size) and the result is 
now added to the *next* element in the summing buffer etc. 

once the sum of a complete analysis window has been calculated (this takes 16 
DSP ticks when your block size is 64 and the [env~] window size is 1024), the 
elements of the summing buffer are shifted one element to the front, the front 
(= sum of the most recent window) itself gets popped and passed to the outlet 
(where it is converted from power to decibels).

the powtodb function takes care of taking the square root of the sum but it's 
done in the logarithmic domain where it's just a division by two.

with smaller hop sizes you basically just get more frequent updates while 
maintaining a larger window size but with more CPU cost.

this is at least how I understood the code.

> Gesendet: Donnerstag, 23. März 2017 um 10:54 Uhr
> Von: "Orm Finnendahl" <orm.finnend...@selma.hfmdk-frankfurt.de>
> An: pd-list@lists.iem.at
> Betreff: Re: [PD] how does env~ work?
>
> Am Donnerstag, den 23. März 2017 um 01:34:58 Uhr (-0300) schrieb
> Alexandre Torres Porres:
> > howdy, help file says "The analysis is "Hanning" (raised cosine) windowed."
> > 
> > how does that work? I tried looking at the code and got no clue...
> 
> In the object's new method, the object allocates a buffer ("buf") and
> writes the Hanning function with RMS compensation (the two nested
> divisions by npoints) into it.
> 
> > 
> > I assume it's not just passing the input through a hanning window, and one
> > way or another,
> 
> That's exactly what it does. The Hanning window emphasizes the middle
> of the analysis window and by adjusting the hop size in the second
> argument of env~ you can fine tune the results.
> 
> --
> Orm
> 
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Re: [PD] how does env~ work?

[Orm Finnendahl]

Am Donnerstag, den 23. März 2017 um 01:34:58 Uhr (-0300) schrieb
Alexandre Torres Porres:
> howdy, help file says "The analysis is "Hanning" (raised cosine) windowed."
> 
> how does that work? I tried looking at the code and got no clue...

In the object's new method, the object allocates a buffer ("buf") and
writes the Hanning function with RMS compensation (the two nested
divisions by npoints) into it.

> 
> I assume it's not just passing the input through a hanning window, and one
> way or another,

That's exactly what it does. The Hanning window emphasizes the middle
of the analysis window and by adjusting the hop size in the second
argument of env~ you can fine tune the results.

--
Orm

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[PD] how does env~ work?

[Alexandre Torres Porres]

howdy, help file says "The analysis is "Hanning" (raised cosine) windowed."

how does that work? I tried looking at the code and got no clue...

I assume it's not just passing the input through a hanning window, and one
way or another, it's gotta compensate it, right? But how?

cheers
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