There are quite a few Bartók-recordings from private collections, and most of them were issued on a 4-CD set by Hungaroton (now out of print):
On it are various solo pieces, some performances with other musicians such as Bartók's wife Ditta with whom he performed pieces for two pianos
...and some pieces with orchestra with Bartók at the piano.
Most of them have abominable sound quality, and the one I would like to share here is no exception! The orchestra is hardly audible, and there are atmospheric disturbances, distortions and gaps. Still, it gives a glimpse of how Bartók played one of his most important piano works... an important historic document.
This recording of a 1938 radio broadcast by Radio Budapest was made by a Hungarian sound recording engineer István Makai (1904-1970) with primitive equipment. He wrote books about radio systems and recording techniques:
Makai was asked to make the recording by the poetess Sophie Török (born Ilona Tanner, 1895-1955), a big fan of Bartók and the wife of the poet Mihály Babits (1883-1941):
Unfortunately the cadenza of the first movement (Allegro) is missing, as well as the Presto middle part of the slow second movement (Adagio).
However it is clear that this is a very precise and energetic performance.
In the Adagio one can hear that Bartók as a pianist was influenced by the Liszt-tradition. At the Budapest Conservatory he was taught by István Thomán,
a pupil of Liszt. In the espressivo section he is using rubato, arpeggiation of chords and the asynchronisation of bass and melody notes (playing the bass notes earlier). According to some modern views, these are "Romantic mannerisms"! However, in Bartók's hands, they are simply suitable, expressive means belonging to his versatile style.
Budapest Concert Symphony Orchestra conducted by Ernest Ansermet.