FFmpeg Option 'mix' not found while using arnndn filter

Question

I am attempting to use FFmpegs arnndn filter (https://ffmpeg.org/ffmpeg-filters.html#arnndn) to denoise audio samples. I am able to run this command ffmpeg.exe -i "input.mov" -af arnndn=m="bd.rnnn" "output.mov" and I receive a denoised output, however when I add the mix option (for example: ffmpeg.exe -i "input.mov" -af arnndn=m="bd.rnnn":mix=1 "output.mov") I receive an error that says "Option 'mix' not found". Am I passing the mix value incorrectly or is this filter not working properly?