Reading same article (see previous post), their research suggests that brain is actually more sensitive to inter-aural group delays than group delays in one ear. The interaural sensitivity goes down to 30uS. Funny, that's exactly what I discovered last year, I could tell the differences in interchannel delays down to 0.03ms (the min adjustment on my Tact is 0.01ms) which is the same as 30uS. That's the same as 1cm physical adjustment of speaker position, or just less than half inch. That sounds familiar.