What is unique about the sound of a harmonium compared to other keyboard instruments?

The sound of a harmonium is unique primarily because it "sounds as written." This means that the notes produced by the harmonium align closely with the written notation, allowing musicians to achieve the intended pitch and timbre without the need for complex adjustments, which can be the case with some other instrumental methods.

In contrast, other keyboard instruments might involve various techniques for sound production, which can add complexities. For instance, in the case of an instrument that uses strings, like a piano, the sound might be influenced by the attack of the key and how the strings resonate.

While it may appear that the harmonium could have limitations in terms of range or its association with rhythm from drum beats, these aspects do not define its unique sound. The harmonium's ability to maintain fidelity to the musical score is what sets it apart. This quality is especially appreciated in genres that prioritize melodic clarity, such as Indian classical music, where the harmonium is frequently used.