In IDEAL-type sequences, spectral selective pulses are done with an excitation frequency f dependent on the slice position, and the acquisition is applied with a reception frequency f. For a proper spectral study, the phase observed during the di erent evolution times of each shot (TE) has to be dependent only on the CS. A phase coherent f-f switch is applied throughout the pulse sequence. However, depending on the frequency commutation position, phase errors are accumulated, disturbing the CS study. This presentation elucidates the impact of the commutation's position and how to correct to resulting phase errors.