In this paper, the accuracy of the analysis of rapidly varying formants using spectrogram and linear prediction is assessed. Analysis of various dynamic signals shows that, when a long analysis window, like 25 ms, is used, the quality of the representation may be impoverished. Obvious unwanted effects are staircaselike formant tracks, flattening‐off of formants close to voicing onset, and bending of the formant towards a strong energy concentration in the release burst. The parameters that have the largest influence on the quality of the representation are the length of the analysis window, the transition rate of the formant, the fundamental frequency, and the position and energy of the release burst. It is shown that the most accurate analysis using a quasistationary method is made when windows are positioned pitch synchronously. Finally, a quantitative analysis of the influence of the mentioned parameters provides evidence that no deviations due to the quasistationarity assumption occur when the effective length of the analysis window is not larger than the pitch period. The wideband spectrogram is expected to be a reliable speech‐analysis tool because it meets this condition for fundamental frequencies up to 370 Hz.