I am using Ardour 5.11.0 on Ubuntu 17.10, and I am trying to use the Rubberband Stereo Pitch Shifter (version 1.8.1).
I need to transpose down 3 semitones using this tool, but it refuses to let me. It will not tranpose -3, but -2 and -4 are no problem. There are also other transposing numbers that it refuses to do, such as -9 and a few others.
I assume it’s a number-box in a generic plugin window… If so, that’s a bug in Ardour 5.11’s GUI widget. You can work around this by showing the automation-lane of the parameter and use the slider or numeric-entry.
Alternatively you could just use Ardour’s build-in pitch-shifting tool (Region > Edit > Pitch Shift) which also uses rubberband under the hood and apply the change instead of doing it live.