I have trouble describing it but you can hear it for yourself with the right tune. There was a unique sound in popular music as the 70's began and it still strikes me as a sound that didn't last into the later years of the decade.
Now take a guy like Wilson (Mac Daddy) Pickett as an example. Wilson is an American Original in every sense of the word from a time when I was just a kid in middle school. Go back to the year 1971 and take a listen to Wilson Pickett to get a sound that I feel was unique to the early 70's: