I don't know of any metronomes that will actually change tempos, but some metronomes can be programmed for less common rhythms. Again, I don't know of any that can be programmed to beat to multiple rhythms within a given piece.
Those that can be programmed can simply be commanded to give a special sound on the first beat of the bar, so if you set it for 7/8 rhythm, then every 7th beat there will be a different sound to indicate the first beat of the bar.
Nor do I know of any metronome that can be programmed to accept constantly changing rhythms. However, your basic metronome can be used for irregular rhythms since the beats themselves will occur at regular intervals; it's just up to you to do the counting.
There are metronomes that can be programmed for polyrhythms; perhaps that is what you are thinking of. They can be programmed, for example, to "click" three against four, or four against six - any number of combinations of polyrhythms, but only two different rhythms at a time. If set for three against four, for example, the three beats per bar will have a different sound from the four beats per bar and each first beat of the bar will coincide.
Dr Beat DB-90 seems to be one of the more complex metronomes available, but I would never buy one for the few times that my basic metronome doesn't give me all that I need.
Click here :
DrBeat DB-90 Their on-line description is not clear to me. For example, what does this mean : "to instantly create a variety of beats by adjusting the levels of five different note values"?
Regards,