Scaler 3.3 AU in Logic Pro causes persistent high CPU after Audio Detection

Scaler 3 Support Bug Reports
1

Dear Scaler Support,

I would like to report a reproducible CPU issue with Scaler 3.3 when used as an Audio Unit instrument in Logic Pro.

My setup:

  • Scaler 3.3
  • Logic Pro 12.3
  • macOS
  • Intel iMac 27-inch, 2019, Core i9, 64 GB RAM
  • Scaler 3 loaded as a Software Instrument / AU
  • Audio supplied to Scaler via Logic’s Side Chain input

The issue is specifically related to Audio Detection.

I performed the following controlled test in an otherwise empty Logic project:

  1. Create a new Software Instrument track.
  2. Load Scaler 3.
  3. Leave Scaler idle for several minutes.
    • Logic CPU usage remains low, around 5–6%.
  4. Select an audio track as Scaler’s Side Chain input.
    • CPU usage remains normal.
  5. Select “Detect Audio” in Scaler, but do not start detection.
    • CPU usage remains normal.
  6. Start Audio Detection, play a short audio section through the Side Chain, then stop detection.
  7. Do nothing afterwards.

Within a few seconds after completing the Audio Detection, Logic Pro CPU usage rises dramatically, in my case to around 100% CPU in macOS Activity Monitor, even though Logic is stopped and no audio is playing.

The high CPU load then persists indefinitely and causes the iMac cooling fan to ramp up significantly.

Closing the Scaler window does not resolve the issue. Removing other Scaler instances does not resolve it either. Quitting Logic Pro immediately returns CPU usage to normal.

I repeated the test carefully and the behaviour is reproducible:

  • Scaler 3 AU loaded but unused: normal CPU
  • Side Chain selected: normal CPU
  • Detect Audio selected: normal CPU
  • Audio Detection performed and stopped: persistent high CPU after a few seconds

The Scaler 3 standalone application does not show this behaviour on the same machine.

This suggests that after Audio Detection is completed, a processing thread may remain active in the Logic/AU version instead of returning to an idle state.

I would be happy to provide Activity Monitor screenshots or perform additional diagnostic tests if useful.

Best regards,

John