This paper deals with analysis of the machining process sound spectrum at milling of the glass-polyester composite material. The development of intensities of the machining process with a growing flank wear has been observed during the experimental machining. High speed steel cutting tools deposited by (Al,Ti,Cr)N coating were used for experimental machining. The goal of this article is identifying relations between the sound generated by the milling process with respect to other measurable variables, which include flank wear of cutting tool and cutting force (or the specific cutting force). The results were compared with results reached during similar milling of the hardened steel DIN EN 10 277 (1.8159).