Overwrite characteristics of digital magnetic recording sometimes include resonant behavior. This behavior can be observed clearly if the write level in overwrite process is varied independent of that in writing old data. In this condition, the overwrite erasure rate a shows a sharp drop at a specific write wavelength λ_0 and a specific overwrite level K_0. In this paper, these values of λ_0 and K_0 are measured for various recording parameters such as the write level K_w in writing old data, write head gap length g_w, medium thickness δ, and the ratio of overwrite to overwritten wavelength λ_e/λ_w. The essential factors determining the resonant behavior are investigated by normalizing those observed data. In a normalized fashion, the value of λ_0/δ can be given as a function of K_w, g_w/δ and λ_e/λ_w. In a large g_w/δ range, λ_0/δ is almost proportional to g_w/δ, while it becomes constant as g_w/δ goes samller.