A drum sound equalizer, called INTER:D, is described that enables a listener to control the volume and timbre of bass and snare drum sounds in commercial compact-disc recordings. Although the characteristics of the drum sounds are often closely related to the impression made by a musical piece, conventional graphic equalizers cannot adjust their characteristics because they have volume sliders only for the frequency bands. INTER:D provides drum-specific volume sliders that directly control the frequency components of drum sounds, enabling a listener to intuitively cut or boost the volume of each drum. In addition, INTER:D enables a listener to replace the original timbre of each drum with another timbre selected from a drop-down list. These interactive functions are achieved using an automatic music content analysis system based on low-level audio signal processing. This system can estimate the power spectrogram of each drum sound and detect the onset times in a musical piece. Subjective experiments showed that INTER:D can add a new dimension to the way users experience music.