The correlation between the frequencies of pressure oscillation ωosc and the rotor speed (frequencies of rotor rotation ωRR) under established rotating stall were determined by three methods: directly from the time diagram of the oscillation process, from the behavior diagram of parameters in space and time and from frequency characteristics. In total accordance with the Theory of Nonlinear Oscillation, by all methods of analysis, the links are in the form of integer ratios: ωosc / ωRR = 1:2 (for n/ nd= 0.6, where n - rotor speed in the experiment and nd- rotor speed from data-sheet) and ωosc / ωRR = 3:7 (for n/ nd = 0.8 and 0.95). The phases of parameter oscillations in the transverse cross-section are equal to the sensor angles in compressor stator. This is in agreement with the theoretical concept of single-cell configurations of rotating stall.