A clarinet mouthpiece and tuning barrel system includes a mouthpiece with a central mouthpiece bore passing through the mouthpiece from a tone chamber to a rear portion of the mouthpiece opposite the tone chamber. The mouthpiece bore has a rectangular cross-sectional geometry extending along an entire length of the mouthpiece bore. This rectangular geometry includes two pairs of opposing parallel sides. Each pair of opposing sides is separated by a unique distance such that a ratio of unique distances for the two pairs of opposing parallel sides is ⅝. Also included is a tuning barrel attached to the rear portion of the mouthpiece. This barrel has a central barrel bore in communication with the mouthpiece bore that passes completely through the barrel. The barrel bore has an identical rectangular cross-sectional geometry to the mouthpiece bore cross-sectional geometry along an entire length of the barrel bore.