The TX81Z is a 1-unit rackmount FM synthesizer first released in 1986. It uses four operators and can use other waveforms than sine, 8 in total, and was the first FM synthesizer to allow programming with alternate waveforms. It has 8 different algorithms available, unlike the 32 available on 6-operator FM synthesizers. A keyboard version was released as the Yamaha DX100.
It has 8 notes of polyphony and is 8-part multitimbral. It has 128 factory patches in 4 banks of 32 and also has a single bank of 32 user-programmable memories. It can load patches from Yamaha's DX21, DX27, DX100, and FB01 synthesizers. Though the DX9 is a four-operator FM synthesizer, its patches are not compatible.
The TX81Z also supports microtuning, with 11 ROM preset and 2 user-programmable intonations.
It is known to have been used by Astral Projection, Future Sound of London, Josh Wink, and Squarepusher.