@ArthurBarthur I’m glad the ConstantQNRTSettings worked out for you. My guess is that it was either a blip that occured when calculating the ConstantQNRT or some edge cases with the settings. For future reference, you can run into a situation where the ConstantQ is looking for frequencies that don’t exist in the audio file.
For instance, if you have a sample rate of 48kHz, the maximum frequency in your audio file is 24kHz. Then, if you have some settings that look at 100 bands, your upper bands may go beyond 24kHz.