The highest notes on a clarinet can have a shrill piercing quality and can be difficult to tune accurately.[5][page needed] Different instruments often play differently in this respect due to the sensitivity of the bore and reed measurements. Using alternate fingerings and adjusting the embouchure helps correct the pitch of these higher notes. Since approximately 1850, clarinets have been nominally tuned according to 12-tone equal temperament. Older clarinets were nominally tuned to meantone. A skilled performer can use his or her embouchure to considerably alter the tuning of individual notes or to produce vibrato, a pulsating change of pitch often employed in jazz.Vibrato is rare in classical or concert band literature; however, certain clarinetists, such as Richard Stoltzman, do use vibrato in classical music. Special fingerings may be used to play quarter tones and other microtonal intervals. Around 1900, Dr. Richard H. Stein, a Berlin musicologist, made a quarter-tone clarinet, which was soon abandoned. Years later, another German, Fritz Schüller of Markneukirchen, built a quarter tone clarinet, with two parallel bores of slightly different lengths whose tone holes are operated using the same keywork and a valve to switch from one bore to the other.