Dual-channel for FFT Spectrum isn't working

Hi,

When I try to use Dual-channel for FFT it just create an green bar over the dock info area as shown below:

<img width="3641" height="992" alt="Image" src="https://github.com/user-attachments/assets/d27b3d2b-f8bd-4cfc-9e56-80b1976e66cc" />

How to reporduce

1. Set input to Two Channels
2. Set FFT Spectrum to Dual Channel

System info
OS: Windows 11
App Version: Friture 0.54