Apparatus and methods are provided for reducing coherent noise in measurements of repetitive analog signal waveforms by digital signal averagers. Coherent noise is repetitive and synchronous with the signal waveform and is therefore undiminished by conventional signal averaging techniques. A major source of coherent noise is the repetitive voltage transitions that occur within the digital signal averager itself. The apparatus and methods of the present invention introduce a known and variable phase offset during the signal averaging process between the signal waveform being measured and the internally generated coherent noise, thereby allowing such coherent noise to be averaged, and therefore reduced, during the signal averaging process. Consequently, the apparatus and methods of the present invention allow greater signal-to-noise ratio and signal dynamic range than with the prior art.