Speech quality models usually estimate the integral quality of the degraded speech files. Such quality values do not inform system developers and telephone service providers on the perceived degradation introduced by the system under study. This paper describes a new intrusive speech quality model, called Diagnostic Instrumental Assessment of Listening quality (DIAL), providing diagnostic information in both narrow-band and super-wideband contexts. Contrary to previous methods, this model estimates scores on four perceptual quality dimensions, Directness/Frequency content, Continuity, Noisiness and Loudness. These four dimensions are assumed to define the whole speech quality space.