The Roland Rhythm 33 (sometimes known by its model number, the Roland TR-33), is a preset drum machine (or "beatbox"), produced by Roland in 1972.
It was one of a trio of drum machines released by Roland that year, offering the fewest features out of its siblings the Rhythm 55 (TR-55) and Rhythm 77 (TR-77). It has an unusual "L" shape, being designed to be mounted on the underside of a keyboard such as an electronic organ.
"TR" stands for "transistor rhythm".
The Rhythm 33 had analogue voice circuits to produce its drum sounds, and offered approximately 20 permutations of preset rhythms.
Roland Rhythm 33 Wikipedia
The Rhythm 33's drum voices are listed below. The sounds are generated by analogue synthesis techniques, and, as is typical with this technology, the sounds themselves, although possessing a certain musical charm, are not particularly realistic imitations of their acoustic namesakes.
The following voices are generated by "tuned resonance" type circuits:bass drum
The following voices are generated by shaped white noise:snare drum
The only control on the front panel for adjusting the sounds is a balance control, which alters the relative levels of the bass drum and the cymbal/hi hat/maracas sounds.
The Rhythm 33 offers the user around 20 preset rhythms. There is no way to adjust the preset patterns per se, or to program your own patterns. The only control available is a (uncalibrated) knob to adjust the tempo, and a push-button which doubles the tempo. However, it is possible to select more than one rhythm at once, and also to effectively "mute" drum sounds from a pattern using the balance knob (see above), thus providing more possibility for rhythmic variation than might initially seem feasible.
Main preset patterns:waltz
rock and roll
Additional "variation" patterns:"2 beat":
bass & snare drum
bass & snare drum
The Rhythm 33 can not interface with other instruments (e.g. to synchronize its tempo with another machine).
The Rhythm 33 has a low impedance mono audio output, available on an unbalanced phone connector socket.