Okay, after further testing I found out an interesting correlation:

The sluggish feel of the program increases when raising screen resolution.

I noticed that the slow UI was much worse on my 5K iMac Pro than on my 12" Retina MacBook (both running macOS Big Sur, with the MacBook having a much slower Intel Core m5 CPU).

To test this theory, I went to macOS System Preferences and increased the (virtual) screen resolution (to 3200x1800):


This made the sluggishness even worse and the bar display delay went up from half a second to a whole second!

So I reduced the resolution (to 1600x900):

This improved things fundamentally.

Next step: I went to Applications, selected Band-in-a-Box.app and pressed Cmd+i to show the inspector. There I checked »Open in low resolution«


When starting BIAB with this checkbox marked, the UI looks quite blurry, but it improves UI performance very very much!

Clicking somewhere into the program results in an almost instant reaction of the user interface and when playing back songs, the bar/chord display is much closer to real time than before.

@Andrew:

I hope this helps to locate the problem.

Additionally:

It seems like the sluggish UI and the delayed chord display are two independent issues:

In my tests, I connected my Airpods to my iMac and selected them as playback device for BIAB. Even in the highest resolution (and the most 'sluggishness' of the UI), the chord display had NO delay! I don't know if this has to do with CoreAudio, but it seems like when using the AirPods, the audio driver reports its buffer size correctly unlike when using the internal iMac speakers.

With the correct buffer size, the display gets compensated properly (and is in sync with the audio).

Last edited by bolandross; 01/15/21 11:36 PM.