This paper presents a new audio mixing algorithm which avoids comb-filter distortions when mixing an input signal with timedelayed versions of itself. Instead of a simple signal addition in the time domain, the proposed method calculates the short-time Fourier magnitude spectra of the input signals and adds them. The sum determines the output magnitude on the time-frequency plane, whereas a modified RTISI algorithm estimates the missing phase information. An evaluation using PEAQ shows that the proposed method yields much better results than temporal mixing for nonzero delays up to 10 ms.