The relationship between pitch and frequency is not simple. The physical frequency for a pitch can be derived in several ways. One example is the Pythagorean s

The relationship between pitch and frequency is not simple. The physical frequency for a pitch can be derived in several ways. One example is the Pythagorean system where the interval of fifth is set as a frequency ratio of 3/2. This system yields clearly distinct frequencies for D# and Eb. In 12 tone equal temperament, a semitone is set as a frequency ratio of 2^(1/12). In this system you get the same frequency. You can also derive frequencies from simple fractions of the scale root. In this instance you would generally obtain D# and Eb from unrelated roots.