A self-oscillating modulator operates at a two-level output. The modulator comprises an alternating output stage (13), an optional output filter (14), a feedback (16) including a function block with a transfer function (MFB), a forward block (12) having a transfer function (MFW) and is provided with means (17) for calculating the difference between the signal originating from said function block and a reference signal. The output voltage of the modulator either from the alternating output stage (13) and/or the output filter (14) is fed back through the function block, and a multiplication element (11) is placed together with the forward block (12) before the alternating output stage (13).