It was Costello's pop expertise, however, on which von Otter wanted to draw when she proposed a collaboration. I tend to see 'crossover' as taking some music that is regarded as difficult and dumbing it down. The key seems to have been restraint in all things, from the quirky, spacious arrangements to the soft, almost hushed quality of the vocals. It's like the difference between stage and movie acting. Loud doesn't matter - it's all tone.
Pop singers tend to have small, thin tone that cuts through.
Anne Sofie has a huge spectrum that you don't often hear in pop. This was brought home to Costello when it came to recording harmonies for the first of several duets. There was no room left for my voice. So there are only a few bars where we actually sing together. To these untrained ears, the quality of the singing is quite mesmerising, yet the precision of delivery and slightly precious air of perfectionism seems to conspire against soulfulness.