Just as the magnetic pickup liberated the guitar in the 50's and allowed it into the 'big band' era, maybe to partly answer Richards original question, the microphone has 'liberated' the human voice. Singers both male and female are now able to use areas within their vocal range that would not have been practical just using the unamplified voice. As 'folk' music acclimatises itself to the 21st century, singers are experimenting with the new technology available to them.