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Au plugins starting late?


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Hi all, I use the silent way ‘sync’ plugin to send a clock and run signal to external gear. After you press play in logic, sync waits until the next bar line to start. However, if I am in cycle mode and the cycle starts at the beginning of a bar, the plugin does not start immediately when I press play. Instead, it only gets going one bar into the loop. This means that every time I use cycle to work on a loop, I have to move the left locator back into the previous bar, then move it back whilst it is playing- very cumbersome and slows workflow considerably.


I asked the maker of silent way plugins and from what I understood he said this behaviour is because the AU plugin format starts late and so doesn’t capture info right at the start of the cycle. The plugin does seem to start corrctly at the start of a loop if I use the VST version in Maschine.


So, is my problem really irresolvable because it is an issue with the AU format, or is there some workaround or setting I can use?


Any help or ideas greatly appreciated!

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  • 1 month later...

Hi Dewdman, I use Silent Way's Sync plugin to synchronise hardware sequencers via control voltage. The way the Sync plugin works is that it sends out a start pulse on a CV channel through my soundcard on the first barline that the playhead crosses after you press play in logic. That gets all the sequencers going.


So if I set a two bar cycle in Logic with the beginning and ends on barlines, and then press play, I want the plugin to send the start pulse out immediately so that the hardware sequencers start at the same time as Logic does.


This *is* what happens if I run the plugin as VST in a different DAW (e.g. Maschine), but in logic, the Sync plugin does not send the start pulse until one bar into the cycle. This seems to suggest that the AU version of the plugin is not starting right on the barline, even though the cycle starts on a barline, and therefore the playhead is starting form a barline.


So I wanted to know if this was a known behaviour of the AU plugin format (this is what the developer suggested) and whether there's anything that could be done about it.


Let me know if I can provide more details to help - thanks!

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-Yes it is an au instrument plugin. Perhaps I could try it as FX?

-I don't usually have any plugin latency comp on, but I can experiment with settings

-I think this behaviour happens regardless of whether I have other channels and/or plugins but I will check this - thank you


Triplets, Sync sends data out in control voltage form through a DC-enabled soundcard, so it’s just short voltage pulses which sound like ‘clicks’ if you monitor the channel. Left channel sends a clock, which you can set as 24ppqn, 48 or whatever, and the right channel sends the start and stop pulses.

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LPX pdc works as follows:


  1. instrument and audio channels with latency inducing plugins will have the regions fed to them early in order that rendered audio will be sample accurate to the beat clock
  2. aux and output channels with latency inducing plugins will cause all other tracks and the clock to be delayed so that their rendered output will be sample accurate.


It’s possible that the cv plugin in question has some latency but since it is generating the sound itself, a midi region is not feeding it, the sound would be delayed, and it’s possible that the cv plugin’s own code mistakenly understands the beat position and this has to wait for the next bar.


I suggest you contact the maker of the cv plugin to resolve the issue. There could be something about LPX latency compensation that this plugin is not taking into account correctly when determining whether to send the pulse. You should also try to determine whether it is actually sending the pulses on later barlines exactly on the beat or if it’s a bit early or late, which might give a clue.


Sorry I can’t think of any other thing right now

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Update: I've found that if I apply plugin delay compensation to all channels and enable playback pre-roll, then put a latency-inducing plugin on another channel (I used Neutron2), I can get Sync outputting at the start of the first bar of cycle as intended. It doesn't seem to matter whether Sync is inserted as an instrument or as FX.


Seems a shame to have to artificially induce latency, but it is a workaround. I'll just have to see whether it is practical in different workflow situations.

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