KLANG:app on macOS shows only a black window and never starts

On some Macs KLANG:app opens a black window with the spinning wheel and never gets any further. There is no error message and no crash report, and reinstalling or trying older versions does not change anything.

The app is not crashing. It is waiting for macOS: one of the first things KLANG:app does at start-up is ask the system MIDI service for the list of MIDI devices, and on the affected Mac that service never answers. In every case we have seen so far the reason was a third-party MIDI driver that is not compatible with the installed macOS version, typically after a macOS upgrade. The Waves / SoundGrid MIDI driver is a known example.

1. Confirm it. Open Audio MIDI Setup (Applications > Utilities) and choose Window > Show MIDI Studio. If that window also hangs or shows the spinning wheel, the MIDI service is the problem, not KLANG:app.

2. Restart the MIDI service. Open Activity Monitor, type MIDIServer into the search field, select it and click the X in the toolbar to quit it. macOS starts it again automatically. Then start KLANG:app.

3. Remove the driver. If it hangs again, in Finder press Cmd+Shift+G and go to /Library/Audio/MIDI Drivers/. Move the third-party drivers in that folder to your Desktop (nothing is deleted, you can move them back), restart the Mac and start KLANG:app. If you have Waves or SoundGrid software installed, start with its MIDI driver, or disable the driver in the Waves software.

4. Start KLANG:app without MIDI (6.0.10 and later). If you need the driver, KLANG:app can be told to leave MIDI alone. Quit KLANG:app, then in Finder press Cmd+Shift+G and go to ~/Library/Containers/com.klang.klangapp2/Data/Library/Application Support/KLANGtechnologies/Autosave1. Open KLANGapp.ppf with TextEdit and add the line <VALUE name="AllowMidi" val="0"/> directly above the closing </PROPERTIES> line, save, and start KLANG:app. In this mode MIDI remote control and local audio monitoring are off; everything else works as usual. Set the value to 1 or delete the line to switch MIDI back on.

If none of this helps, please contact support with a sample of the hanging app: while the black window is on screen, open Activity Monitor, select KLANGapp, click the gear icon and choose Sample Process, then attach the saved file.