This paper describes research into signal transformation operators allowing to modify the vibrato extent in recorded sound signals. A number of operators are proposed that deal with the problem taking into account different levels of complexity. The experimental validation shows that the operators are effective in removing existing vibrato in real world recordings at least for the idealized case of long notes and with properly segmented vibrato sections. It shows as well that for instruments with significant noise level (flute) independent treatment of noise and harmonic signal components is required.