Most filters can emphasize the frequencies just before those that are reduced in volume. Resonance is the degree of emphasis that occurs. It makes the filter much more audible and gives it character - it would otherwise sound like just altering the equalisation - and is the foundation of the acid sound....
Prodigy
"The Prodigy is what Moog personnel came to know as the "bootleg Moog." Designers
[Rich] Walborn and [Tony] Marchese concocted the Prodigy on the quiet They wanted
to see if they could build a '$500 Moog,' and they did just that. They simply dumped it on
the marketing division weeks before the Winter NAMM show and said, 'Here it is, give it
a name.' To the Moog marketing team's eternal credit, they scraped themselves off the
floor and did just that.
"This clean-lined synth offers two oscillators and limited but high-quality filter and
modulation controls [with a 2 1/2-octave, 32-note (F-C) keyboard].... Prodigy was
Moog's biggest seller next to the Minimoog.
"Both oscillators have a switchable choice of sawtooth, triangle or pulse (narrow on osc
1, square on osc 2) waveforms, and they can be pitched within a two-octave range. Osc
1 calibrates this as 32' to 8' and osc 2 from 16' to 4'. An interval knob can split the
voices up to a fifth apart, and a sync switch smartly lashes them back together again for
those searing, forced tones that remain de rigeur in the Jan Hammer school of lead
synth playing. A small mixing panel offers independent control over the level of each
oscillator, plus a master volume.
"At the time, Moog made much of its 'heated chip' technology -- not a culinary term, but
a method by which Moog hoped to cure the perennial problem of oscillators drifting out
of tune. But the Prodigy made only a negligible improvement in this regard, and
prospective purchasers are wise to leave an instrument on for a while to see how well it
performs.
"The 24dB/oct lowpass filter features standard cutoff frequency and resonance (Moog
persisted in calling this 'emphasis') controls and a slightly limiting ADS envelope
generator. [There is a separate ADS envelope generator for each of the VCF and the
VCA.] The filter can track the keyboard (fully, half on or off) and is good for self-
oscillating, whistly ghostly noises. Modulation is limited, with a square- and sine wave-
only LFO capable of modulating either or both of the VCO and VCF.
"There's a lot more Walborn and Marchese could have put on, of course, but that's not
the point here. They were designing to a very tight, albeit selfimposed, financial brief,
and the spinoff benefit is that no one gets frightened or bamboozled with sample-and-
hold or a squillion modulation sources and destinations on a Prodigy.
"The basic sound of a Moog synthesizer is still here, not classically so, and not
particularly flexibly so, but with portamento and a pair of stiffish mod and pitch wheels
(which I trust will have eased up a bit on most models by now), you can crank out some
nice squelchy bass lines and more. The oscillator hard-sync sounds work particularly
well.
"Encased in wood [maple], the unit's basic construction was of good quality, which
means they stand a chance of survival. Some of the panel hardware was of less sturdy
stuff, so some knobs and switches might need to be replaced." [Earlier models had no
external control inputs. Later models have CV/S-trigger inputs and outputs, as well as
inputs for pitch, VCF and sync control.]