Harmonica was introduced in Blues in the days of unamplified delta blues, also known as country blues. It was used as rhythm instrument as well as a solo. Musicians like Sonny Terry and Brownie McGhee played a vital role in establishing its place in the Blues music.
Later on, harmonica was only used as a solo instrument in Blues. When subgenres of Blues such as Urban Blues, Chicago Blues and Little Walter style were developed, the harmonica was heavily amplified and it changed its tone from natural to synthetic. However, Blues harmonica still has a mild tone that makes it calming and pleasing. Now, the musicians understand that they can do experiments in other genres and this Blues music can only carry a simpler version of harp.
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There is a school of thought that believes the harmonica found its spot in Rock music through Blues and Country music. This is right to some extent but there were lot of musicians who were already using unusual instruments in this genre of music. In Rock, harp is played in “bent” style with much less amplification. Harmonica is used as solo and rhythm instrument in Rock music. Though, it depends on the player’s likes and dislikes but in general harp is played in more melodic “light rock” style.
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