Tones 4 and 8 of Hanoi Vietnamese have strongly contrasting voice quality features: tone 4, which is glottally constricted, is here compared with a similar but nonconstricted tone (tone 8). Under emphasis, the slope of F0 curves is increased and/or F0 register is raised. The open quotient values (calculated from the derivative of the electroglottographic signal, which has been shown to yield very accurate values) do not vary significantly with emphasis. A description in terms of curve amplification is put forward. As for changes in length, they appear to be speaker-dependent.