The VF-11 is an 11-band analog vocoder from German company MAM (Music And More). A vocoder lets you create robotic vocal effects. You basically feed two sounds into it, the sound you want to process (Synthesis Input) such as a synth lead or synth pad, and the sound that will do the vocoding (Analysis Input) such as your voice or a drum loop.
The Analysis input has mono Mic and Line inputs. The signal you plug in here will be separated into 11-bands which cover a frequency range of 50Hz to 12kHz. The unique frequency spectrum of the analysis input sound will have different amplitudes at each of the 11 analysis bands. So a low frequency specific sound will generate lots of voltages in the low frequency bands, but very little to no voltages among the higher frequency analysis bands. The amount of voltages generated by these bands depends entirely on the harmonic content of the Analysis sound input.
Voltages generated by these analysis bands go on to control up to 11 Envelope Detectors on the Synthesis channel. The Synthesis channel is also split into 11-bands and each band passes through a VCA envelope controlled by these Envelope Detectors. The end result is that the Synthesis input's envelope is generated by the harmonic content of the Analysis input sound.
The VF-11 has its very own, albeit very simple, analog VCO to use on the Synthesis channel in lieu of external audio. This oscillator offers only a sawtooth waveform with a simple pitch adjustment knob. The VF-11 has only a mono output which can output the processed or unprocessed signals. The VF-11 can also function as a filterbank! Plug a sound to the Synthesis channel, and nothing into the Analysis channel. Then you can adjust the gain of each of the 11 bands. It isn't resonant, but it works. The VF-11 is analog and affordable. There's no MIDI or memory and you'd need two of these to process stereo audio. It's a good 'starter' vocoder but no replacement for the classic vocoders.
Demos & Media
Images from MAM - Music And More.