[PD] weird behavior of [vd~] in phave vocoder (overlapping subpatches)

[Alexandre Torres Porres]

naaah, yeah, they're different.. oops... but doesn't really make any
difference perceptually... let me check it some more...

2015-09-10 17:49 GMT-03:00 Alexandre Torres Porres <porres at gmail.com>:

> yeah, I have to sit again with some time and figure it out, I should do
> some tests to better understand how many objects behave. But, in the
> meantime, lets talk about something important here.
>
> > Delaying the back window [z~] is a rather lazy trick and it won't
> > give accurate results each time you change the pitch shifting
> > factor, but after one fft-window it settles. The question is if you
> > can actually here this error. When I find some time I'll make a
> > comparison between our both solutions.
>
> Are you really sure about this? Cause I've been testing it and thinking
> about it and, in my opinion, both are exactly the same thing, equally
> equivalent, and I can't hear any difference as well.
>
> Lets sort this out ;)
>
> I think that the second delay makes it a simpler patch and easier to
> understand. I'm using [cyclone/delay~] by the way, which works with samples
> - must be the same thing as [z~].
>
> cheers
>
> 2015-09-10 14:23 GMT-03:00 Christof Ressi <christof.ressi at gmx.at>:
>
>> Hmmm, since we basically agree on all these things I was thinking if I
>> missed a point, because I simply don't believe that [vd~] behaves
>> differently than [tabread4~] and there is any unlogical or 'special'
>> behaviour with [vd~] within an upsampled subpatch. Maybe one thing: The
>> input of [vd~] is a time in milliseconds which is interpreted according to
>> the actual sample rate (because internally the delay lines work on samples,
>> of course). In that way it behaves like [phasor~], [vline~], [osc~]. So
>> when you send 1000 ms to a [vd~] in a subpatch with overlap 4, the delay
>> line will be read at sample 176400 (supposing the [delwrite~] is in a
>> subpatch with sample rate 44100). This is not an issue if both the
>> [delwrite~] and [vd~] are in the same subpatch. But if they are in
>> subpatches with different sample rates you have to make some adjustments.
>> If you're also aware of this behaviour than I don't know what else we
>> could've missed...
>>
>> Cheers
>> *Gesendet:* Donnerstag, 10. September 2015 um 18:10 Uhr
>> *Von:* "Alexandre Torres Porres" <porres at gmail.com>
>> *An:* "Christof Ressi" <christof.ressi at gmx.at>
>> *Cc:* Pd-List <pd-list at lists.iem.at>
>> *Betreff:* Re: Re: [PD] weird behavior of [vd~] in phave vocoder
>> (overlapping subpatches)
>> yeah, it'll consider the signal input is 0 so it'll output the
>> corresponding index - which is "1" because of the interpolation.
>>
>> and yeah, I'm aware they're both buffer readers, delwrite~ / vd~ being a
>> circular / ring buffer. And my point was this difference between them,
>> where delay lines will always read/output at regular speed.
>>
>> But that is not the core of the discussion, and we actually agree on it,
>> so I'm not sure what we're talking about here.
>>
>> My point was just that [vd~] acts in a special way when in an overlapping
>> subpatch, and that is it'll output the audio without discontinuities or
>> pitch shifting because of interpreting the overlap as oversampling. That
>> behaviour is special when compared to [osc~], [phasor~] and I also tried a
>> buffer reader like [tabplay~] and got "bad" results. They all don't work
>> well in it, and so does not [vline~] by the way. There might be other
>> relevant objects to test but I'm just not thinking about it. Nevertheless,
>> I have the idea most will have problems, while some, like [vd~], will be be
>> fine.
>>
>> The thing about [tabread~] is that it solely depends on external sources
>> to read the buffers, while [vd~] doesn't, and that makes quite a practical
>> difference in my opinion. The deal with [tabread~] is that the issue is
>> more about what object is driving it and how it behaves (such as [vline~]
>> and [phasor~], which don't behave well with overlapping subpatches).
>>
>> But again, not a relevant discussion. But I do feel like making more
>> tests, I just don't know if there is a possible to test to check how the
>> behaviour or [vd~] and [tabread4~] could relate between themselves.
>>
>> > For me its sometimes a trial and error game to find all
>> > those parameters which have to be divided/multiplied
>> > by the overlap factor. But after a while of thinking
>> > everything turns out to make sense.
>>
>> yeah, it was trial and error, but I'm still not 100% sure how it makes
>> sense... hence this thread :) - but I guess I'll keep thinking more about
>> it.
>>
>> > Delaying the back window [z~] is a rather lazy trick and
>> > it won't give accurate results each time you change the
>> > pitch shifting factor,
>>
>> that's important to note, and that's why miller's patch may not have been
>> using this procedure.
>>
>> thanks
>>
>>
>> 2015-09-10 6:39 GMT-03:00 Christof Ressi <christof.ressi at gmx.at>:
>>>
>>> "Oops, now I'm the one to say you can't compare them as equal. You see,
>>> [tabread~] needs to have an audio input to read through the array, but
>>> [vd~] is always "reading" the buffer at normal speed - so this makes them
>>> quite different. Since [tabread~] only react if some signal is feeding it,
>>> then it depends solely on that incoming signal; and thus the object who's
>>> outputting it, which could be [phasor~] or [vline~]. So it's more about
>>> which object who's driving it than itself."
>>>
>>> Again, I insist that the behaviour of [tabread4~] and [vd~] is
>>> equivalent ;-). When you don't feed any input to [tabread4~] it outputs the
>>> value at index 1. Now try to think of a delay line as simply a table which
>>> content is constantly updated at a time interval of 1/SR (SR = the actual
>>> sample rate of the subpatch containing the [delwirte~]). If you don't send
>>> any signal to [vd~], it behaves just as [tabread4~], only that the value at
>>> index 1 always changes, so it only appears that [vd~] itself is reading
>>> along a buffer. (Note that both objects can't read index 0 because of the
>>> 4-point interpolation algorithm. So with [vd~] you will never get less than
>>> a one sample delay.)
>>> To make sloppy analogy:  [tabread4~] would be a band machine where the
>>> tape itself stands still why the tape head can be freely moved, whereas
>>> [vd~] would be one where the tape runs at a fixed speed and additionally
>>> the tape head can be moved too. Well, I don't know if this makes sense :-).
>>>
>>> Since you took the word "reading" in quotation marks you might be aware
>>> of all this. In that case the confusion might arise from the fact that you
>>> have to consider the relation between the 'speed' of the delay line
>>> (depending on the sample rate of the subpatch containing the [delwrite~])
>>> and the 'speed' of the object providing the input for the [vd~].
>>>
>>> Please anyone correct me if I'm wrong on these points!
>>>
>>> For me its sometimes a trial and error game to find all those parameters
>>> which have to be divided/multiplied by the overlap factor. But after a
>>> while of thinking everything turns out to make sense.
>>> Delaying the back window [z~] is a rather lazy trick and it won't give
>>> accurate results each time you change the pitch shifting factor, but after
>>> one fft-window it settles. The question is if you can actually here this
>>> error. When I find some time I'll make a comparison between our both
>>> solutions.
>>>
>>> Cheers, Christof
>>>
>>>
>>>
>>>
>>> *Gesendet:* Donnerstag, 10. September 2015 um 07:51 Uhr
>>> *Von:* "Alexandre Torres Porres" <porres at gmail.com>
>>> *An:* "Christof Ressi" <christof.ressi at gmx.at>
>>> *Cc:* Pd-List <pd-list at lists.iem.at>, "Gerd Schuller" <
>>> studio at gerdschuller.com>
>>> *Betreff:* Re: [PD] weird behavior of [vd~] in phave vocoder
>>> (overlapping subpatches)
>>> >>> unlike [osc~], [vd~] will get the continuities between blocks
>>> right!"
>>>
>>> > You can't really compare these two objects.
>>>
>>> Sure I can :) i'll insist on it by the way. Again, [vd~] will not
>>> generate discontinuities with the overlaps, unlike other objects such as
>>> [osc~] and [phasor~]. Moreover, and as a logical result, it won't change
>>> the pitch because of the oversampling. It'll just work fine.
>>>
>>> > [vd~] is actually the same thing as [tabread4~]
>>>
>>> Oops, now I'm the one to say you can't compare them as equal. You see,
>>> [tabread~] needs to have an audio input to read through the array, but
>>> [vd~] is always "reading" the buffer at normal speed - so this makes them
>>> quite different. Since [tabread~] only react if some signal is feeding it,
>>> then it depends solely on that incoming signal; and thus the object who's
>>> outputting it, which could be [phasor~] or [vline~]. So it's more about
>>> which object who's driving it than itself.
>>>
>>> When it comes to [vd~], the pithc shifting and time stretching also
>>> depends on the object that's driving the input, which could be again
>>> [phasor~] or [vline~] and need to deal with their behaviour.
>>>
>>> > you have to divide by the overlap factor, because then
>>> > you read less samples and therefore virtually slow the
>>> > [vline~] down. In a subpatch with overlap 4 everything
>>> > happens 4 times as fast because instead of only 1 block
>>>
>>> yeah, sure, I've pointed it in my 1st message. I get that.
>>>
>>> But as I asked, I don't really get how ALL parameters need to divided by
>>> 4, not only the [vline~] time, that is not clear yet. Sorry.
>>>
>>> And by the way, my patch does also time stretching, so it's different
>>> than yours and is dealing with more parameters and issues than you. So you
>>> are addressing the [vline~] issue only (replaced by [phasor~] in your
>>> patch) - but that was the only parameter that I really understood anyway.
>>>
>>> > When using [z~] to delay the back window simply by the
>>> > fft hop size you don't have to care about  window sizes
>>>
>>> hmm, my problem was more why were my two patches different, the one with
>>> fft needed to care about it, but the other one didn't. I actually get why
>>> that thing needs to be done to properly phase align the windows.
>>>
>>> So I was thinking and then thought that the other patch was working
>>> because it wasn't a phase vocoder, so the phase alignment was not
>>> important. But now that you say this and showed your patch, I can see that
>>> you need not worry if you are using a delay. And I was actually using a
>>> delay in my non fft patch.
>>>
>>> In the end my patches were different but equivalent and now I get why.
>>> It's cool to know and learn that if you are using delay you don't need to
>>> care about it.
>>>
>>> thanks
>>>
>>> ps. I'm still curious on sorting out the behaviour of [vd~] though
>>>
>>>
>>>
>>> 2015-09-09 7:54 GMT-03:00 Christof Ressi <christof.ressi at gmx.at>:
>>>>
>>>> Hi Alexandre,
>>>>
>>>> I'm new on this list, but I think I can help you on this because
>>>> recently I tried to do the same thing. I can't fully test your patch
>>>> because I'm missing the cyclone library (and don't bother to install it
>>>> :-p).  I try to give an answer to the following questions:
>>>>
>>>> "Other issues related to overlapping besides this "oversampling" is
>>>> that some objects won't make it right, they'll chop the blocks with
>>>> discontinuities, such as the case with [osc~]. But as it turns out, unlike
>>>> [osc~], [vd~] will get the continuities between blocks right!"
>>>>
>>>> You can't really compare these two objects. [vd~] is actually the same
>>>> thing as [tabread4~], only that it reads from a ring buffer rather from a
>>>> table. So the critical thing is only which object you use as the input for
>>>> [vd~]. You are using [vline~] whereas I'm using [phasor~]. Both are
>>>> equivalent. For the reading index for [vd~] you have to divide by the
>>>> overlap factor, because then you read less samples and therefore virtually
>>>> slow the [vline~] down. In a subpatch with overlap 4 everything happens 4
>>>> times as fast because instead of only 1 block, 4 blocks have to be
>>>> processed - in the same time!). My approach is to have a [phasor~] run from
>>>> 0 to 1 (or 1 to 0) for every block so I have to multiply it's speed by
>>>> four. Than I multiply the output by the windows size. Note that in my patch
>>>> I get the second window one hop size behind by simply delaying it with [z~]
>>>> whereas you've chosen to use a second [vd~] with a wrapping object. (I
>>>> guess you're way actually saves some memory as you don't need a second
>>>> delay line).
>>>>
>>>> "And even more weirdly, in the Pvoc patch I have to multiply the
>>>> difference between the front and back windows to the ratio of
>>>> transposition. This is even crazier than the last issue, and I have no idea
>>>> why that has to be this way..."
>>>>
>>>> When you're transposing you're actually reading more samples for
>>>> upwards pitchshifting and less samples for downwards pitchshifting. So you
>>>> basically stretch or compress the window size. This means also that the
>>>> time difference between two windows changes if you want them to be phase
>>>> aligned. If the window gets larger, the time difference to the last window
>>>> also gets larger and vice verca. You might be aware of this: The window in
>>>> the back has to be phase aligned with the front window because you need it
>>>> as a reference to calculate the difference from the actual phase of the
>>>> previous output window.
>>>>
>>>> When using [z~] to delay the back window simply by the fft hop size you
>>>> don't have to care about window sizes and time differences at all. It is,
>>>> however, also a bit incorrect for the first analysis window after a change
>>>> of pitch so I might change it and try it your way!
>>>>
>>>> You can have a look at my solution and compare it to yours. From what
>>>> I've seen both work the same way though I couldn't test your patch.
>>>> However, I think that my patch could be conceptually easier to understand,
>>>> but I might be wrong :-).
>>>>
>>>> Cheers, Christof
>>>>
>>>> PS: Ignore the right half of [pd read-windows] with the two
>>>> [tabread4~], this is only needed for the freeze effect.
>>>>
>>>
>
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