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The Yamaha FVX1 is a super rare MIDI-compatible FM Voice Expander that comprise the expanded system of the HX Series Electone. An AWM epxander was also available: the Yamaha AVX1. The FVX1 has four 8-operator FM tone generators on board, representing a "timbre", that can be layered through an internal mixer. Much like the TX81Z or the DX11, multiple waveforms are available for each operator. Each timbre or layer has 8 notes of polyphony and can be controlled independently via its own MIDI channel.
The FVX1 holds 248 preset voices, 256 user-programmable memory slots and 16 performances. Yet the parameters that can be directly accessed by the user from the front panel are rather limited in comparison to its full synthesizer siblings: the frequency, output level and waveform of each operator, as well as the envelope generator rates and levels. An external computer editor, called the FED1 FM editor (built specifically for the Toshiba T3100), has to be used in order to gain full control on the voice editing capabilities.
Similarly to what is offered on the DMP7 and DMP11, the onboard mixers also has additional effects available: Stereo-Chorus, Stereo-Pan, Symphonic, Phaser, Flanger, Delay, Tremolo, Digital hall, Celeste and Wah.