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The most important ability to produce a good quality and variety of tone is to be aware of the varying points of contact between the bow and the strings between the fingerboard and the bridge. Allied with this is the awareness of the appropriate speed of the bow at its varying points of contact with the string as well as the necessary arm weight. The bow will have to move much slower when it is close to the bridge of the instrument in order to avoid a scratchy sound. The reverse is compared to over the fingerboard where a more transparent sound will be achieved. The command of these varying points is so important if you wish to obtain the widest range of sound.
Once a player has full command of all the different positions that the bow can have then it is possible to and perform a piece so as to convey the "passions" of the music to an audience.
Finally, should you move into the higher positions on the instrument, then any given contact point will in turn move closer to the bridge.
