Some notes on hoover/mentasm synthesis which might help:
Use a pulse wave and modulate the pulse-width heavily with a very fast sine/triangle LFO - That's it!
For some reason it only really sounds right on Alpha Junos... I think maybe the alpha junos let you use PWM on saw tooth waves aswell - This may be something to do with it... I've got the JunoX VST kicking around somewhere, those hoover noises are the only things that sound remotely Juno in it!
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The best LFO PWM wave to use would be a triangle wave, as that is the only LFO waveform available on the Alpha Junos. When used as a modulator a sine wave can sound quite different, and you will notice.
That might still not sound quite right though, as the Alphas also let you use PWM to modulate the width of two gaps in a sawtooth wave, and that might have been the technique used in the sound you have in mind. Unfortunately I'm not sure how this could be recreated in a modern soft/VA synth, although my best guess is that it would involve amplitude modulating a sawtooth wave with a pulse wave one octave higher, then modulating the width of the pulse with an LFO.
Does anyone know exactly which preset inspired the hoover sound?
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The preset in the alpha Juno's called "What The...!" - Yeah I've got myself a Juno now - My 106 can do the Hoover noises but there definetly is something a little different to the alpha Juno's Hoover sounds - Basically, the Juno's LFO can go very fast and the PWM is much wider than on most other synths - The Hoover sound is a Pulse Wave with fast and quite wide PWM, played along side a Square Wave Sub-Oscillator 1 Octave Lower - Both going through a pretty open Low Pass filter - Not really much to it..
I think it's just one of those sounds that only a Juno can do properly - I can't get it on any other synth I've used - At least not as authentic sounding...
Everyone needs a Juno - MKS-50's and alpha Junos are absolute bargains at the moment! They won't be for ever - I can see their 2nd hand value going through the roof unless someone comes up with a decent new analogue polysynth or two in the future. The plug-in Juno is good for the Hoover sounds but rubbish at just about everything else - Can't even touch the Juno's awesome pad sounds let alone the bass.