Using (8.146), derive an expression for the ratio of the noise power in y_D(t) with de-emphasis to the noise power in y_D(t) without de-emphasis. Plot this ratio as a function of W/f₃. Evaluate the ratio for the standard values of f₃ = 2.1 kHz and W = 15 kHz, and use the result to determine the improvement, in decibels, that results through the use of dc-emphasis. Compare the result with that found in Example 8.3.