1.9.9 iSem and Viking AU performance

Hey there,

I just upgraded with the release of 1.9.9, and am noticing large CPU spikes when using audio unit synths. I have been playing with a brand new project, which has a single AU instrument (iSem or Viking), and when idle, the CPU shows nothing. But when I press a key on the keyboard, the CPU spikes up to 50%+ while notes are being played. When I record this and add a second AU instrument, the CPU is all over the place. I have even seen the CPU shoot up to the top momentarily when the first key is played.

Even going back and playing previous projects that I never notified this, shows the CPU all over the place.

Plus I am not sure if this is a bug or not, but I can’t save settings within the Viking Synth AU

Hi fotizimo,

Please share more information regarding your system in use:

  • iOS device
  • iOS version
  • Project Info (Sample rate, latency setting etc.)

Furthermore please check if restarting the iPad and Cubasis helps to solve the issue.

Regarding AU preset saving:
Apple’s AU preset handling is limited to loading presets as of yet.
We’ve informed them about it during the implementation phase and they promised to discuss the preset save request internally. Other AU instruments such as iSEM AU show up with their own preset system that allows to load/save presets.


Hey there,

So I am running:

iPad mini 2 128gb with LTE V9.3.1

I have reloaded the iPad and the problem persists. When I open a project with even a single iSem AU instrument, and play a few notes, the CPU spike almost to the top and then settles down around 25% while playing single notes. Multiple notes or chords and the CPU will go a little higher. It isn’t steady, it fluctuates, but even in tracks with many audio and midi channels, my CPU never really goes all that high, unless an AU is present.

I have been thinking of this problem today, and now can’t recall if I saw the CPU behave like this previously on 1.9.8 with AU units, but I do tend to keep an eye on the CPU gauge and would most likely have noticed this.

So I do not create large projects, as I am still learning about music production, I just wanted to bring this up in case it might be a bug or something. If there is something I can do to help troubleshoot, please let me know.

So something I have just been finding, and do not know if I should post a new topic, is when I open a project that has a few AU’s, Cubasis takes some time to open the individual AU’s, but when I go to play them, there is no audio. The CPU still spikes as I mentioned before, but Cubasis doesn’t play any audio from the AU. I see the transport indicator move along, and I see the midi notes in each lane, but there is no audio from the AU’s.

Has anyone else noticed this type of behaviour before? At this point, I basically can’t use iSem, or Viking Synth for more than one instrument.

Hi fotizimo,

Please double check that the AU instruments in the project are properly loaded, by opening their interfaces in the AU instrument rack.

In some cases, AU instruments fail to load and need to be manually re-loaded by tapping the corresponding button in the AU instrument rack or re-loading the project.

Please also have a look at the limitations of Audio Unit extensions we’ve released in the topic back with the 1.9.8 release:


Hope that helps,