Electri-q and Posihfopit phase behaviour in VSTAnalyser

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I've been checking out the "how do you judge an EQ" thread with much interest, and I've been tweaking around with Christian's VSTAnalyser to see what I can see... very cool program Christian!

I've noticed some odd behaviour with your plugins though... Electri-q and Posihfopit seem to have some weird phase behaviour:



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Electri-q (Analog) flat curve



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Posihfopit flat curve



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Electri-q (Linear phase mode) flat curve



Something seems to be going on... My guess is that it's a bug in the VSTAnalyser, because the phase behaviour indicated on the graphs certainly isn't what I'm hearing... But I thought I'd post it up anyway for your interest Christian... :)

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That's the problem with the analyzer. What you see in both cases (it seems) is called linear-phase response. If it was a group delay plot you would see a straight line. Phase response plot is generally a hardly reasonable measurement of filter's sound. But it is simple to plot, of course.
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Aleksey Vaneev wrote:That's the problem with the analyzer. What you see in both cases (it seems) is called linear-phase response. If it was a group delay plot you would see a straight line. Phase response plot is generally a hardly reasonable measurement of filter's sound. But it is simple to plot, of course.
Indeed it's due to the oversampling filters. Try 'eco' to see the response phase shift free.

Kind regards,

Christian

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OK cool Christian, I thought something was up... thanks!

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Christian Budde wrote: Indeed it's due to the oversampling filters. Try 'eco' to see the response phase shift free.
It is not necessarily due to oversampling. A simple sample delay will produce a similar plot (if you won't do a compensation). And, of course, any linear-phase filter will produce a similar plot as well.
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Aleksey Vaneev wrote:
Christian Budde wrote: Indeed it's due to the oversampling filters. Try 'eco' to see the response phase shift free.
It is not necessarily due to oversampling. A simple sample delay will produce a similar plot (if you won't do a compensation). And, of course, any linear-phase filter will produce a similar plot as well.
Right, but in my case it's because of the polyphase oversampling filter, which introduces some delay which leads to this behaviour. These kind filters seem to be very popular nowadays (ok, my girlfriend hates them or at least if I talk about them. For her that are huge monsters with thousand tentacles, muahhhahaaaa)

Kind regards,

Christian

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Christian Budde wrote:These kind filters seem to be very popular nowadays (ok, my girlfriend hates them or at least if I talk about them. For her that are huge monsters with thousand tentacles, muahhhahaaaa)
:lol: :lol:
I think it is hard to find a girlfriend without a similar attitude ;-)

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Aleksey - PLParEQ does not give a similar plot, that was part of the reason for me posting this thread...

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mustgroove wrote:PLParEQ does not give a similar plot, that was part of the reason for me posting this thread...
I guess PLParEQ simply doesn't have oversampling. Also the filter is applied in a different manner (if I remember correctly). The filter is "rendered" in the frequency domain which is put into a huge FIR filter (basically an impulse response which is used by a convolution engine). I think CurveEQ works similar, and in Linear/Maximum- Phase Mode Electri-Q can work the same. If you select the "S-Plane" filter types you can even achieve the perfect bell symmetry (which usually isn't the case for digital filters).

Kind regards,

Christian

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Christian Budde wrote:
mustgroove wrote:PLParEQ does not give a similar plot, that was part of the reason for me posting this thread...
I guess PLParEQ simply doesn't have oversampling.
it does.

'Sinc Interpolation on Upsampling'

'Upsampling of low SR audio provides faithful filter shapes all the
way to Nyquist frequencies.'

from the manual.

edit: i can't find those 's-plane' filters?

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In my opinion that curve is linked to the plug-in delay (even if already compensated). For example, Waves L2 has the same curve as a generic plug with 64 samples delay. I don't think Waves is making upsampling for a limiter plug. I sent a mail to christian about 5-6 months ago for this subject. In my opinion L2 doesn't change phase. It changes gain only, after 64 samples of look-up ahead.

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defjamm wrote:edit: i can't find those 's-plane' filters?
In version 1.5.2 only in linear/maximum- phase mode -> "S-Plane"
leban wrote:In my opinion that curve is linked to the plug-in delay (even if already compensated). For example, Waves L2 has the same curve as a generic plug with 64 samples delay. I don't think Waves is making upsampling for a limiter plug. I sent a mail to christian about 5-6 months ago for this subject. In my opinion L2 doesn't change phase. It changes gain only, after 64 samples of look-up ahead.
In the version I made public there is no way to manually change the delay used for analysing. If the plugin reported 64 samples although it has about 65 samples, then you will find at least one phase wrap. I should have enabled the "group delay" view. Delay is sometimes easier to understand then phase.

Kind regards,

Christian

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Christian Budde wrote:
defjamm wrote:edit: i can't find those 's-plane' filters?
In version 1.5.2 only in linear/maximum- phase mode -> "S-Plane"
leban wrote:In my opinion that curve is linked to the plug-in delay (even if already compensated). For example, Waves L2 has the same curve as a generic plug with 64 samples delay. I don't think Waves is making upsampling for a limiter plug. I sent a mail to christian about 5-6 months ago for this subject. In my opinion L2 doesn't change phase. It changes gain only, after 64 samples of look-up ahead.
In the version I made public there is no way to manually change the delay used for analysing. If the plugin reported 64 samples although it has about 65 samples, then you will find at least one phase wrap. I should have enabled the "group delay" view. Delay is sometimes easier to understand then phase.

Kind regards,

Christian
yes, but your analyser says that plug reports correctly all the samples. Infact L2 has no delay on cubase sx!
I have a plug with a configurable delay, reported correctly to the host. I have the same slopes on the phase plot. When I set 64 samples I have the same plot of waves!!

btw: this plug is a bypass

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I can also confirm that engaging "econ" mode does not change significantly change the phase behaviour shown above... it's still wildly all over the place...

Not that I'm too concerned about it really... I'm sure it's down to some kind of mathematical quirk of the plugin or of the analyser itself, doesn't make Electri-q any less awesome-sounding :D

Putting Electri-q on the master in Analog or Screaming mode with no bands engaged adds so much niceness to tracks...

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mustgroove wrote:I can also confirm that engaging "econ" mode does not change significantly change the phase behaviour shown above... it's still wildly all over the place...
Have you restarted the measurement? Or are you using the Phase reduced filters? The basic 'eco' settings with normal filter types don't any delay and thus shouldn't produce any phase wrap.

Kind regards,

Christian

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