This is a re-release of one of Decca's most famous recordings, the Allegri Miserere from the 1960s recorded by David Willcocks and the King's College Choir, alongside Palestrina's Stabat Mater. It is an absolutely immaculate performance, recorded to the best of Decca's specialist art in capturing in-situ performance. However, compared to today's recordings you will find that it is very 'hissy', despite remastering with the best of digital technology.
Palestrina's Stabat Mater has never really done anything for me -- I much prefer the Pergolesi -- but the Allegri Miserere goes through me like a knife. In this version it is sung in English, a good choice, since the text from Psalm 51 works closely with the music to weave one of choral music's most compelling sacred pieces.
Personally I'm very happy with this recording, despite the hiss. However, if CD audio quality is your main concern, you will need to look elsewhere.