Arvo Pärt evidently never considers a work finished. For those of us who consider his music as perfect as is humanly possible, this striving for improvement seems redundant, yet he almost always astonishes us by revealing even more breathtaking perspectives.

As well as writing variants of many compositions (I think Fratres holds the record with around 11 different scorings: the ATMA album features the string quartet version) he often revises the originals. For example, Psalom, his only extant work originally intended for string quartet, was composed in 1985, revised in 1991 and again in 1997. That (so far) final version is the one the Franz Joseph Quartet use here.

Performers sometimes prompt new versions. Jackson and his cohorts decided to use early instruments tuned to A=415Hz, a common Baroque pitch. The rationale for these period-costume recordings is that, when Pärt developed his tintinnabulary style in the mid-1970s, a rebirth of interest in early music in Estonia acted as ‘a midwife on my new music’. In practice, the difference is hardly dramatic, and it is hard to tell whether it is pitch, the character of the instruments or the approach of the musicians which distinguishes these performances.

Both albums provide a good introduction to Pärt’s work. For me Black Box wins the cigar, but it’s a very close-run thing. While the ATMA disc appealed most to my inner voluptuary, my tough reviewer’s carapace responded to Black Box’s inclusion of the Sonatinas (the official Op 1 dating from 1958-59) as a commendable reminder of the young Pärt’s strict Modernist stance. His early repertoire is increasingly neglected (though Neeme and Paavo Järvi did their best to keep it in the public consciousness) and these solo piano pieces provide a radically contrasting context for Pärt’s later, better-known style. (Anorak alert: No 1 was only previously available by Bruno Lakk on a 1959 10in Melodiya LP, No 2 on a 1971 12in LP, performed by Mart Lille.)

The albums have only two direct points of comparison, Es sang and Stabat mater. Jackson takes the Stabat mater at a slower pace, using a 13-member choir against the solo soprano, countertenor and tenor voices of Chamber Domaine’s recording. Jackson’s choice better exploits the shimmering beauty of Pärt’s lines and harmonies, but the smaller forces permit a more personal identification with the sorrow of the poetry.

On Es sang, a setting of an early 19th-century German Romantic poem, Pärt’s methodological fingerprints are as clearly evident as ever, but his melodies are unusually expansive. Stephen Wallace’s performance is superb, better than his rather too operatic stance on Stabat mater, where Helen Meyerhoff takes the prize. The ATMA recording is, again, probably more attractive texturally and stronger technically, with fine string performances and Daniel Taylor producing utterly gorgeous sounds; but there is an appealing humanity about Wallace’s interpretation. Despite the large number of Pärt collections already available, these are both well worth having.