This paper presents two exploratory experiments aimed at establishing a lexicon suitable for the description of the sound quality of flue organ pipes. A lexicon of reference was established by an expert organ-builder commenting several voicing steps performed on a flue pipe. This lexicon was then extended, the purpose being primarily to enhance communication between and among organ builders, acousticians and musicians. In the first experiment a qualitative analysis was made of data collected from a listening test in which a number of specialists on organ performance, music theory, history and building took part. The 40 participants made ratings and gave comments to ten recordings of pipe sounds through the voicing process. By comparing an analysis of participants’ comments with a primary list of descriptors defined by an organ builder, an attempt is made to extend this primary list to a more standard lexicon. A temporary classification of these descriptors is proposed and is reviewed in a companion paper oriented towards a quantitative analysis of this type of data. In a second experiment, a dimensional analysis of data collected from a semantic differential test based upon the descriptors found in Experiment 1. From a quantitative analysis the initial "qualitative" categorisation is reviewed and enhanced. By inspecting the factor structure of the descriptors, groups of related descriptors were formed and suitable prototypes of each group were proposed. We then show how, from original data extracted from free comments, a detailed classification of descriptors can be made.