[TheOtherHobbes]

Analog vocoders are only nominally like analog FFTs.

The shape of the filters, the smoothing between the filters and the synthesis section, and (on some models) the patchability all create a very different result.

The reason the best analog vocoders are so expensive is because the filter for each band is much more complex than a plain old bandpass filter, with a much higher component count. Typically there's a flatter passband and a steeper slope than you'd expect.

You can do digital convolution with thousands of bins and it sounds nothing like analog vocoding. It's much cleaner, doesn't have those lovely harmonically spaced filter resonances, and creates sounds that can feel more acoustic than electronic.