▁a ▁compilation ▁album ▁by ▁the ▁Beat les , ▁and ▁is ▁an ▁alternate , ▁all - m ono ▁version ▁of ▁the ▁album ▁Past ▁Masters . ▁Mon o ▁Masters ▁was ▁originally ▁a ▁two - CD ▁set ▁included ▁as ▁part ▁of ▁The ▁Beat les ▁in ▁Mon o ▁box ▁set . ▁The ▁prem ise ▁of ▁this ▁box ▁set ▁was ▁to ▁compile ▁only ▁Beat les ▁material ▁which ▁was ▁released ▁or ▁prepared ▁for ▁release ▁with ▁a ▁dedicated ▁mon o ▁mix ▁( the ▁set ▁ex cludes ▁later ▁material ▁mixed ▁and ▁released ▁only ▁in ▁s tere o , ▁and ▁material ▁whose ▁mon o ▁version ▁was ▁simply ▁created ▁as ▁an ▁equal ▁mix ▁of ▁the ▁two ▁channels ▁of ▁the ▁s tere o ▁version , ▁i . e ▁ 1 9 6 9 ' s ▁Y ellow ▁Sub marine ▁album ). ▁As ▁a ▁result , ▁the ▁track ▁listing ▁for ▁Mon o ▁Masters ▁diff ers ▁from ▁Past ▁Masters ▁on ▁the ▁second ▁half ▁of ▁disc ▁two , ▁om itting ▁some ▁later ▁songs ▁that ▁never ▁had ▁a ▁mon o ▁mix ▁(" Old ▁Brown ▁Sho e ", ▁" The ▁Ball ad ▁of ▁John ▁and ▁Y oko " ▁and ▁" Let ▁It ▁Be "), ▁and ▁adding ▁several ▁songs ▁released ▁on ▁s tere o - only ▁albums ▁that ▁had ▁un re leased ▁mon o ▁mix es . ▁Tra cks ▁ 9 – 1 2 ▁and ▁ 1 5 ▁were ▁prepared ▁in ▁March ▁ 1 9 6 9 ▁for ▁release ▁as ▁a ▁ 7 " ▁mon o ▁Y ellow ▁Sub marine ▁EP , ▁two ▁months ▁after ▁the ▁release ▁of ▁the ▁similarly