While normally the player simply plays both the tremolo reeds at once, it is possible to achieve a wide variety of bends and other effects through selecting certain reeds and chambers and not others.
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This allows the player to isolate each reed. Hohner's Marine Band) the blow and draw reeds do not share a common chamber, but are separated off from one another. Unlike the standard ten-hole harmonicas (built on the "Richter system", e.g. In practice, however, it is common for each individual reed to have its own air chamber. In this design the two beating reeds are distributed one on each reed-plate (top and bottom) and these share a common chamber. Most tremolo harmonicas are built upon what is termed the "Wiener system", named after the city of Vienna (Wien in Austria) where they first emerged. This effect is fairly common amongst Western free-reed instruments and is found in accordions, harmoniums and reed organs under various names (celeste, vox jubilante, etc.), but it is also used, for example, on the piano, where each of the three strings is tuned very slightly sharper or flatter, giving a richer sound to the instrument. The resulting sound is of constant pitch but the volume oscillates between loud and quiet. Each note is played simultaneously by two reeds, fractionally out of tune with each other. The tremolo harmonica achieves the effect by employing the physical phenomenon called beats. Most orchestral instruments achieve this effect by repeated playing of a single note. " Tremolo" is most often defined as a periodic change of volume (sometimes incorrectly defined as a change in pitch, strictly vibrato).