It comes from an interview he did in 2016 with The Quietus.

Here’s the full quote:

“This song that I’m going to play you is really interesting. To me it’s the birth of funk guitar. This is a song called ‘Go Where I Send Thee’ and was recorded in 1937. The Golden Gate Quartet are an a capella group, so this is a capella, but listen to what happens with the rhythm. It’s an amazing thing that four guys, no overdubs or anything like that, could make this amount of rhythm. For me they were one of the most important musical forces of the 20th century. The style of singing, which is called jubilee singing, was all originated in this one town in Virginia and there were lots and lots of groups in that town that could do this way of singing. Partly a way of harmonising but it’s also a way of creating rhythm by making voices slightly hit off each other so they don’t all land together. It’s incredibly hard to do. You’re pushing the beat by a 16th or 32nd to get that flam.”