Translate tempo into musically related pre-delay values, then tune by ear around the source.
Start with a timed value, then shorten it until the dry vocal stays clear. Genre and phrasing matter more than mathematical purity.
At 120 BPM
Pre-delay values
1/4500 ms
1/8250 ms
1/16125 ms
1/3262.5 ms
1/6431.3 ms
1/8 triplet166.7 ms
1/16 triplet83.3 ms
1/32 triplet41.7 ms
What pre-delay changes
Pre-delay creates a short gap between the dry signal and the first audible reflections. More separation can preserve intelligibility; less separation can make the source feel embedded in the space.