Previously I, along with others, have reported that Audacity playback is sluggish when the aup3 file has multiple tracks, with either a long delay before commencing playback, or stuttering badly, or both. I think that I have discovered the probable (or at least the major) cause. My circumstance is that I use a range of Waves VST3 plugins. I have always suspected that the problem was related to these plugins. I found this explanation on the Waves website: Waves uses background processes called “WavesLocalServer.lnk and WavesPluginServer.lnk” to facilitate cross plugin communications, preset scanning, advanced plugin features and licensing abilities. There is no problem if the service is terminated, but it will be relaunched by the plugin once it is needed. However, be aware of the purpose of this process. According to Waves, it’s just a server so that when you use a multiple copies plugin you aren’t wasting precious resources on loading many copies of it. It makes it so that you only load one copy and everything else references it.
I decided to deactivate it in my startup menu because I felt it was not necessary (and using resources) and then the problems started! Since I have reactivated this background process Audacity playback works as expected. Based on Waves’ explanation above, each of my tracks with plugins was loading their own individual copy of the plugin when I had the background process disabled.
If you are using Waves plugins and are experiencing playback delays/issues, then check your startup menu for the activation status of WavesLocalServer background process. If you’re not using Waves plugins but are having these playback/stuttering issues check what other background daemons from companies like Native Instruments, etc., may be either running or are deactivated. This may be the cause of your problem.