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Modulation Error Ratio (MER) is a measurement used to evaluate the performance of modulation schemes in communication systems, particularly in digital television and data communication. It quantifies the quality of the modulated signal relative to the noise and interference present in the signal.

MER is expressed in decibels (dB), which is a logarithmic unit used to describe ratios. In this context, it specifically represents the ratio of the power of the signal (desired information) to the power of the noise (unwanted interference). By using decibels, engineers and technicians can easily compare performance differences, as a logarithmic scale allows for a more manageable representation of the potentially wide range of power levels encountered in communications.

The choice of decibels is particularly useful in telecommunications, as it simplifies calculations involving multiplication and division into addition and subtraction, making it easier to analyze signal quality under various conditions.