REW Beta Release Alignment Tool Question

[Conrad.]

I've been using the time alignment tool a lot recently and I love it, it's saved me hours of adjusting and re-measuring.
A question around the delay sliders though. On the left is the delay which ranges from -50 to +50 and on the right is the distance which ranges from -56' 3" to 56' 3".
My question is, isn't one of the signs the wrong way around? To add delay in a processor you have to remove distance, so shouldn't a positive delay have a negative distance and vice versa?

I could very easily be misunderstanding something, but it's been a constant source of confusion for me and others I've worked with. Every time I have to make an adjustment and really think about it, and often I'll go the wrong way.

@John Mulcahy , I'd appreciate your thoughts on this.

Thanks

 

[John Mulcahy]

Time is being converted to distance by multiplying by the speed of sound, so a negative delay is a negative distance. From the measurement perspective a larger delay means the source is further away. Processors calculate delays to align to the furthest speaker, so they adjust delays to counter a distance change. I could change the sign of the distance figure, but I don't know that it would make any more sense that way. Happy to hear views on it though.

 

[Conrad.]

Thank John, the way you explain it makes sense.

I'm thinking about it from a workflow perspective though. If I want to add 5ms I need to remove 5' (ish) from the distance. I would imagine that's the most common use case for the time alignment tool, people wanting to see how adjustments will affect their response, and then apply those changes. I may not be considering use cases that I'm not familiar with though.