1. A data reproduction apparatus having a viterbi decoder, the data reproduction apparatus comprising: a storage unit configured to store a first input signal; a frequency detection unit configured to: receive a second input signal; detect a frequency of the stored first input signal from the received second input signal; generate a frequency detection signal indicating that the frequency of the stored first input signal is detected; and generate frequency information of the stored first input signal based on the received second input signal; and a level value determination unit configured to: detect a ratio between the generated frequency information and preset frequency information according to the generated frequency detection signal; convert a sampling rate for the stored first input signal based on the detected ratio; detect at least one level value for the stored first input signal using the sampling-rate converted first input signal; and determine the detected at least one level value as an initial level value of the viterbi decoder.