Repeated public performances including Beethoven Opus 130, 133, Haydn Opus 76, No. 5, Ravel Quartet, Janacek Quartet 2 by a well-known string quartet recorded live over a number of years in various cities and concert halls (a total of 170 entire movements) when analyzed show a striking long term ultrastability of timing; of the order of 0,2–0.6% for a number of fast and moderately fast movements. Stability was as good as that previously observed for single performers including Toscanini (Clynes & Walker, 1982; Clynes 1969). This indicates that shared musical concepts can be highly stable. Slower movements tend to be relatively less stable. Tempo compensation is often present so that if parts of a piece are played somewhat faster, other parts are correspondingly played slower to tend to maintain overall timing (as had been earlier found for single performances). Seven performances of Janacek's second quartet revealed what appeared as quantized small total duration changes. When examined for quantal tempo steps, 84 other performances of movements revealed apparent preferred tempo steps of 0.5% (0.48 ± 0.02). Performances of the first five movements of Beethoven's Opus 130 were all significantly slower when the Grosse Fuge was substituted for the finale. The high degree of stability otherwise observed indicates that environmental factors such as temperature, humidity, size of the hall, and variation of acoustics had little influence on the timing. The findings are significant in relation to the properties of the psychobiologic clocks involved; they show how musical concepts can precisely govern their long-term temporal realization, involving time spans of the order of 30 min., even when shared by four individuals; and further, that such shared concepts can remain stable over periods of several years.