It's believed that Marley wrote the song but gave the songwriting credit to his childhood friend Vincent Ford in order to help him sustain the soup kitchen that he ran in the Trenchtown ghetto. Regardless who wrote it, it's still powerful today. Here are a few things to listen for.
1) It's interesting that the track is built around a primitive drum machine. Considering how formidable Reggae rhythm sections are, you expect the full band to play on every song.
2) The low vocal parts by the Wailers are pleasing out of tune. These probably fall into the "close enough" category so prevalent at the time.
3) The number of keyboards used is also a surprise; 4 organ tracks, a piano, and clavinet.
4) There are two lead vocals, but you can't tell if they were eventually comped together from listening to just this single multitrack pass in the video.
5) The recording looks to be done on 23 tracks of a 24 track tape machine. Track 24 was usually reserved for timecode if needed, but sometimes the edge tracks of the tape were avoided altogether or used for bass and kick drum because they'd be damaged and have limited frequency response.
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