  In the measurement of the amplitude of vibration of objects, holographic
imaging techniques usually involve fringe counting; due to the limited
resolution of images, measurements of large amplitudes are not accessible. We
demonstrate a technique that suppresses the necessity of fringe counting:
frequency sideband imaging, where the order of the sideband is considered as a
marker of the amplitude. The measurement is completely local: no comparison
with another reference point on the object is necessary. It involves a sharp
variation of a signal, which makes it robust against perturbations. The method
is demonstrated in an experiment made with a vibrating clarinet reed; phase
modulations as large as 1000 radians have been measured.
