Multi mono - Singal generator out of phase

[oortone]

ProTools Ultimate 21.10.67
Minimac (ca. 2018)

Can anyone else reproduce this bug:

• Start blank
• Add one audio channel and master out channel
• Add some phase meter at master out
• On the audio channel insert the built in "Signal Generator" as multi mono plug in
• Twiddle the frequency
• Somewhere you will find frequencies that are not 100% in phase L/R

If I close the project (but not necessarily ProTools) and re-open, the phenomenon goes away.
If I add a new track and repeat I get the same phenomenon, not necessarily on the same frequencies. It too goes away if I save and re-open.

[midnightrambler]

Why would you expect 2 different instances (because that's what multi-mono is) of a signal generator to stay in phase when you move frequencies? I'd be more amazed if they did stay 100% locked.

[oortone]

Originally Posted by midnightrambler

Why would you expect 2 different instances (because that's what multi-mono is) of a signal generator to stay in phase when you move frequencies? I'd be more amazed if they did stay 100% locked.

It's not two instances.

I believe Multi Mono is offered to deliver the opportunity to use a plugin that's not available in Stereo or Multichannel to the user. I'd therefore expect it to be in phase which it usually is as far as I know.

Why would the two channels not be in phase when instansiated together and presented in one single plugin window?

[dominicperry]

Originally Posted by oortone

It's not two instances.

I believe Multi Mono is offered to deliver the opportunity to use a plugin that's not available in Stereo or Multichannel to the user. I'd therefore expect it to be in phase which it usually is as far as I know.

Why would the two channels not be in phase when instansiated together and presented in one single plugin window?

Because two different frequencies are, by definition, not in phase.
If you wander off a base frequency and then come back to the original frequency, there is no guarantee that the zero-crossing point will be at the same place. So that will then be out of phase with a separate instance that has never been changed.

[albee1952]

Beyond what Dom is saying(which I tend to agree with), what's the end goal here? What are you trying to achieve(or is it just an experiment that isn't giving an expected result)?

In general terms, I don't think much time was spent creating the signal generator plugin and I would not count on it for critical purposes. Its handy for testing routing, dropping a 1KHz tone and such, but for critical work, I would lean on something else, like the Alan Parsons Sound Check CD or a hardware tone generator

[Rich Breen]

Originally Posted by oortone

It's not two instances.

I believe Multi Mono is offered to deliver the opportunity to use a plugin that's not available in Stereo or Multichannel to the user. I'd therefore expect it to be in phase which it usually is as far as I know.

Why would the two channels not be in phase when instansiated together and presented in one single plugin window?

Multi-mono instantiations of signal generator are not phase-locked. create a mono aux with a single instantiation of sig gen and bus to where it needs to go.

[oortone]

Originally Posted by dominicperry

Because two different frequencies are, by definition, not in phase.
If you wander off a base frequency and then come back to the original frequency, there is no guarantee that the zero-crossing point will be at the same place. So that will then be out of phase with a separate instance that has never been changed.

There're not multiple frequencies in a multi-mono instance of this plugin. There's one frequency - two channels.

[oortone]

Originally Posted by Rich Breen

Multi-mono instantiations of signal generator are not phase-locked. create a mono aux with a single instantiation of sig gen and bus to where it needs to go.

That's interesting. Is this true for all Multi-Mono plugins; that phase coherency is not guaranteed? In that case I don't get what use Multi Mono is meant for.

Thanks for the tip on using an aux instead.

[oortone]

Originally Posted by albee1952

Beyond what Dom is saying(which I tend to agree with), what's the end goal here? What are you trying to achieve(or is it just an experiment that isn't giving an expected result)?

In general terms, I don't think much time was spent creating the signal generator plugin and I would not count on it for critical purposes. Its handy for testing routing, dropping a 1KHz tone and such, but for critical work, I would lean on something else, like the Alan Parsons Sound Check CD or a hardware tone generator

Actually, this was just something I discovered while trying to find an inconsistency in the analog part of my monitor system, so I used Signal Generator to generate different frequencies. Suddenly I saw the channels where out of phase and thought there was someting wrong with the amplifier.

I used a stereo channel just by accident, didn't think there would be a phase issue. In the case of Signal Generator there's no need for a stereochannel but if this phase issue exists in Trim (which is also only available as multi mono) then that's very bad.

[midnightrambler]

Originally Posted by oortone

Actually, this was just something I discovered while trying to find an inconsistency in the analog part of my monitor system, so I used Signal Generator to generate different frequencies. Suddenly I saw the channels where out of phase and thought there was someting wrong with the amplifier.

I used a stereo channel just by accident, didn't think there would be a phase issue. In the case of Signal Generator there's no need for a stereochannel but if this phase issue exists in Trim (which is also only available as multi mono) then that's very bad.

The phase issue exists in the "generation" part, i.e. when you're sliding the frequency up and down even the tiniest amount of delay between the computer processing the left/right movement of the slider will knock the generator out of time (and therefore out of phase) ever so slightly. This isn't going to be an issue with "processing" - or at least you'd hope not, otherwise the whole system would fail, not just one multi-mono plugin.