I’m a little perplexed by this issue. I’m currently running 9.0.10. Yesterday I tried to record a synth chord part with Serum VST. All I had was a couple of tracks in the whole project. When entering the notes in piano roll manually I could have lots of polyphony playing back with no issue. However when I tried to record a keyboard part in in real time, the peak light immediately went on and tempo slowed down and computer totally bogged down. This is on a 12 core 2012 Mac pro with 64G ram. The project settings are 88.2/24.
I tried again in Ableton and I had similar problems (but not as bad). So this is clearly more of a computer issue…but what could be the problem? I can replicate the issue on a brand new project with only the one track. I have tried a couple of different VST synths and I’m getting the same problem. I have a ridiculous buffer size (over 2000). I tried on my little macbook pro laptop and it works fine there!