The effect upon reversible linear-potential-scan voltammetry of adding a modulating square wave of any amplitude is examined by solving the governing equations exactly. This solution explains the origin of the "splitting effect" that had previously been observed empirically in the dc component. The ac component is derived in both the time domain and the frequency domain. In the former, it consists of a periodic function, displaying spikes whenever the square wave experiences a sign change, In the frequency domain, harmonics that possess odd multiples of the square wave's frequency are present, phase shifted by 45degrees. The dependence of the accurrent amplitude on the dc potential and on the square wave's amplitude is formulated. Comparisons are made with a recent simulative and experimental study of the same system.