Utilizing a formulation of output power of a digital beamformer with input quantizers ofunequalinput and output step sizes reported elsewhere [H. S. C. Wang, Quantizer Functions and Their Use in the Analyses of Digital Beamformer Performance (to be published); also see J. Acoust. Soc. Amer.51, 135(A) (1972)], the optimum quantizer step sizes that yield maximum processing gain are searched by the method of “steepest ascent” with a digital computer. For the case of 2 bits/channel quantization with small input S/N (−10 dB), no maximum can be found, and, as the input S/N exceeds −4 dB, the array gain increases monotonically with respect to both input and output step variables. These phenomena were clarified by a numerical study of a “3‐level quantizer” as a limiting case. The large theoretical processing gain at large step sizes is attributed to a threshold effect of the input quantizers.