Hello Thomas,
Any crackles in audio when only a few pipes are sounding will be due to hardware/driver/system performance problems (e.g. most commonly PC DPC latency, or perhaps some audio hardware/driver/USB synchronisation problem, or over-filling the computer's RAM), rather than anything within the audio output that Hauptwerk itself produces. You could verify that by using Hauptwerk's built-in audio recorder, and then playing back the audio files when Hauptwerk isn't running (e.g. on a different computer) -- you should find the crackles you heard at the time aren't present in the recorded audio files.
If you haven't already done so, and assuming you're using a PC (as opposed to a Mac), try working the PC audio performance troubleshooting steps in the '
Performance tuning: Other operating system and computer optimizations and diagnostics' section in the main Hauptwerk user guide (pages 274-276 in the current v6.0.2 version). For example, make sure you keep an ample amount of RAM free, and in particular try leaving LatencyMon (
https://resplendence.com/latencymon ) running whilst Hauptwerk is running and when the crackles occur -- if the PC has underlying performance problems (e.g. DPC latency) then it will probably report them and help to pinpoint which device/driver is causing them.
Best regards, Martin.
Hauptwerk software designer/developer, Milan Digital Audio.