The diagram below was designed by Tatsuro Yatabe as an attempt to clarify the tonal qualities, just as Ruckmick's Tonal Bell.The shade shows brightness: the lower part is darker and the upper part is lighter.The width of the belt shows volume: the lower, the wider, and the upper, the narrower.The spiral of the continuous ascending belt shows octave quality.The breadth of the spiral increases and is broadest at the middle part.This indicates that pitch discriminations are most acute at this part.The number of discriminable pitches is indicated on the right side of the diagram.The upper part which has no spiral, means that octave is not discriminated at this part.'ch', 'f' etc. on the left side which correspond to the 'c' note on the right side are meant to show what is called Kohler's vocality.The limit of a human voice in the diagram is the limit which can be reached clearly, so the actual limit may broader than this.11 ~ w VI c.