The transient sound from an organ pipe is a very important component in deciding the pipe's timbre. This paper addresses the issue of verbal description of transient sounds of flue organ pipes. This problem must be solved when, as in our case, one wishes to document, understand and possibly assist the work of an organ-builder in the process of voicing organ pipes. Therefore, we explain the procedure used to map the relationship between verbal descriptors and quantitative acoustic analyses. The study is restricted to single flue organ pipes (no chords). A procedure integrating both objective and subjective methods is presented in order to develop such a description. After an introduction on basic voicing principles, a list of verbal descriptors used by the voicer is presented and serves as a basis for listening tests and signal analysis. Several types of listening tests are described. Computer implementation of these tests is shown to be particularly useful. Signal analysis using time-frequency methods is employed for separating harmonics and for representing the transient components of the signal. Results are also reported on the perception of the speed of the transient and of the sound “hiss”.