The alternation between voiced plosives and spirants in Iberian languages is described as the complementary distribution between two allophones. The present study explores the acoustics of /d/ in two corpora of spontaneous speech and examines the hypothesis that constriction degree in /d/ is governed by finer-grained speech production factors than claimed before. Three acoustic metrics were developed as indexes of articulatory weakening. The findings suggest that variations in the implementation of /d/ result from gradient modulations in constriction degree on a unimodal, rather than bimodal, statistical-acoustic distribution. The preceding segment is a strong predictor of the weakening (i.e., spirantization) of Catalan and Spanish /d/.

Index Terms: Spanish, Catalan, lenition, phonetics, phonology.