I would suggest you’ll get a better quality sound if you start from scratch and mix your own rather than trying to removal the vocal.
Vocal removal only works depending on how a track is mixed. Audition uses a centre channel extractor to extract the centre of a mix. Music for example usually is stereo where as the vocals are mono and sit in the middle of the mix. Audition works by removing the middle bit but remember parts Music will also be in the middle so you’ll lower the quality of the bit you want to keep.
In your case as it’s probably an atmospheric recording it’s either mono so by removing the centre channel you’d probably also remove the bit you want or degrade its quality significantly. Equally it could be recorded in stereo in which case the speech will also be all over the mix so would be impossible to remove.
For that reason I’d suggest you download the elements you want and mix them yourself.
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