Slightly OT: Moog sound sample

[markusw]

How do get this sound with an anlog synth?  Check out samples "Vowel Bass" and "Hollow Bass". I'd love to get such sounds (or at least this direction) with my bass guitar. I know it would be easier to buy a synth  Nevertheless...
What wave shapes do you think are used, square or triangle (..or a mix)?
Is it likely that filter Q is also voltage controlled via e.g. an envelope??

http://www.moogmusic.com/detail.php?main_product_id=161

Markus

[SeanCostello]

"Hollow Bass" sounds like a few pulse waves mixed together, through a single swept Moog LPF. Not as hollow as I would have thought - normally, a "hollow" synth sound implies square waves.

"Vowel Bass" uses the two parallel Moog LPF filters of the Voyager.

You would want to use square waves, or sawtooth waves, in order to have some harmonics for the resonant peak of the filter to sweep through.

Doesn't sound like voltage controlled Q to me. The original Minimoog and Moog Modular filters had a nice feature, where the Q had a very nonlinear relationship to frequency. For low frequencies, the Q dropped off dramatically, resulting in a better sound for bass (lower Q=less rolloff below resonant peak=bassier). The nonlinear Q was an accident resulting from the AC coupling of the filter ladder to the differential ouput amplifier. Very similar to how the presence control works in the 5F6-A / Marshall circuit, but for low frequencies instead of high frequencies.

Sean Costello

[dirk]

You could make a square wave from your bass by heavy distorting it. Then to get the vowel sound you have to put the square wave through 2 bandpass filters. For the hollow bass you can use just 1 lowpass filter. Don't forget to add a LFO and ADSR/envelope follower.
I think this would make a great stompbox.

[markusw]

Hey guys,

thanks a lot for your informations!! 

Doesn't sound like voltage controlled Q to me. The original Minimoog and Moog Modular filters had a nice feature, where the Q had a very nonlinear relationship to frequency. For low frequencies, the Q dropped off dramatically, resulting in a better sound for bass (lower Q=less rolloff below resonant peak=bassier). The nonlinear Q was an accident resulting from the AC coupling of the filter ladder to the differential ouput amplifier.

Some time ago I checked the Moog low pass filter in LTSpice and I observed exactly what you described    , Q drops at lower frequency. By increasing the coupling caps to the differential amplifier Q at lower freqs increases.

So it will need two filters for the "vowel bass". Now I remember R.G.'s paper about formants...

I'm thinking of doing a Bissell-follower Moog low pass combination (the one from the Minimoog). Haven't yet thought about putting in two filters.
Suppose, it won't fit into a 1590B 

Don't forget to add a LFO and ADSR/envelope follower.

I planned to add an LFO 

Squaring shouldn't be a huge problem. My idea was to have a send/return loop for the filter(s) (like in the Meatball). So a distortion, fuzz or a guitar-2-square wave converter could be put in front of the filter.

If I e.g. use a low pass filter/comparator combination to generate the square wave I suppose I'll also need a VCA fed by the guitar envelope?? Otherwise the square wave signal would have constant amplitude. What do you think??

Edit: would the VCA be after or before the filter(s)??
2nd edit: looking at the Minimoog schems it seems the VCA would be after ther filter.

Will require some more planning.

Again, thanks a lot for your help!

Markus