These are original CDs from Phnom Penh in Cambodia featuring popular singers from the 1960s and 1970s. The music is unlikely to have been taken from master tapes as they will probably have been destroyed during the era of genocide in Cambodia. The source is usually a record or tape which sometimes leads to a lower audio quality.
Somewhere down the line, most of the original source recordings were overdubbed with a modern musical backing track which, depending on your viewpoint, either gives the recording a modern/poppy punch or alters it beyond recognition. These are the versions which have become popular and it is extremely difficult to find unaltered versions.