Since the advent of modern, fast computers, more and more softsynths have emerged. Some, like Rebirth, try to emulate a certain hardware synthesizer - others are just a digitized version of a generic analog synth: oscillators, LFO's and other parts you'd expect in a pre-FM and pre-sampling era musical instrument. The funny thing is that most softsynths recreate the same elements, and still don't sound alike. Somehow, the approach that programmers take makes for a totally unique and independent sound.
So, this is what softsynths do: they try to capture the elements of a real, physical synthesizer in software. Rebirth was made to mimic the TB-303. Most others don't set out to sound like a particular synth, but can be made to sound very TB-like. Another cool thing about softsynths is that programmers can put in cool stuff like distortion, delay effects and so on.. without increasing the cost of the program. In hardware terms, every addition would mean an increase in manufacturing cost. This is the big advantage softsynths have over hardware - price.
The downside (and I'm talking my personal experience here) is that softsynth do have the same peakvalue. What I mean by that is, that compared to 'real' oscillators every softsynth levels out at approximately the same area - really high dog whistle sounds can't be had with ANY softsynth. But don't worry, you don't get them from $$$ analog modelling synths either. Er, analog modelling - wazzad? Well, it's basically the same as a softsynth, except the synth has been put into it's own proprietory box (e.g. a keyboard with knobs). The softsynth inside such a keyboard does basically the same, emulating analog oscillators and LFO's. But because hardware's involved, such instruments tend to be very expensive. So we'll just forget about those.
Softsynths are an inexpensive way to make music or to create useable instruments. Some very cool softsynths are actually FREE! We'll be looking at some and provide you with URL's to try 'm out for yourself. Read on!