3.6. Post classification
3.6.1. Definition of drum 'types' or drum 'classes'
In the vast majority of break beats that will be the subject of this project, the break simply exists as an interactive rhythm played between the kick drum, snare drum and high hat. In these types of break the rhythm played by the high hat could equally be played by a ride cymbal or could be sonically 'doubled up' with a shaker or tambourine. The rhythmic effect would be much the same. Therefore drums of the type cymbal, shaker, high hat or tambourine will be grouped together and simply referred to as the type 'hat'.
These three sounds can be further split into 'soft' hits (usually constituting drums played on off beats or drums played in a 'shuffle' style) and 'hard' hits. Unless drums are defined as soft hits we will assume they are hard hits.
In addition to the above type of break there are many breaks that simply comprise a rhythm played on conga drums or bongos. This rhythm is often an interaction between two or more drums tuned to different pitches. In a recording scenario these breaks are very useful when doubled up with the rhythm of a drum kit. The tuning of congas and bongos can vary greatly between different makes and players. It was thus decided to group both of these drums types together as the type 'conga' and to make distinctions between different tunings that are detected within a break. Drums detected as having the same tuning will be referred to as being in the same 'pitch group', and the tuning of a drum will be referred to as its 'pitch'.
Tom tom drums also occur sporadically in rhythms played on kit based breaks but are much more frequent in breaks representing 'fills' (a fill refers to a rhythm played by a drummer usually before the start of a new section in the music). In a similar way to congas toms are subject to many different tunings. Therefore different tom types within a break will also be distinguished by their tunings and placed into different pitch groups.
3.6.2. Classification Numbers
We will limit ourselves to the above five major drum types and the further distinctions of soft hits and different pitch groups. In addition it will be useful to detect certain common combinations of drum hit that can occur namely kick/hat, conga/hat and tom/hat combinations. Snares contain a great deal of high frequency energy as do hat sounds, therefore we will not make a distinction between a snare and a snare/hat combinations.
Table 1 shows the numbering system of the defined drum types. This numbering system will be useful when placing detected drum types in to the universal drum map and is also a convenient and easy way to refer to the drum types.