Filters explained

Within the Reason package you will have access to four generic filter types:

1. Low Pass Ladder
2. State Variable
3. Comb
4. Formant

These filters are handy tools that help you further shape the frequencies being produced by the oscillators by cutting out or boosting the ranges you want. It is key to look at these filters as only one step of a whole process, isolating the frequencies you want to be modified by other tools in your toolbox. 

The Low Pass Ladder and State Variable filters function using similar algorithms. I have made the following diagram for you to summarize their effects - let the X axis represent the frequency and the Y axis represent the signal's amplitude:

To go into further detail, the Low Pass Ladder is strictly a low-pass filter with various parameters. In Propellerhead's software (and other VSTs), you will notice that there is a 6, 8, 12, 16, and 24 option next to the frequency knob. With these you can set the rate of subtraction in decibels per octave in correspondence to the filter cutoff point. Now that you are thinking in those terms, you can see that it is -6db/octave, -8db/octave, and so on.

Lastly, the Comb filter simply adds a delayed version of the signal to itself. This will in effect add or cancel out certain frequencies along the spectrum being run through the filter. The Comb filter is most effective for creating that wide, ensemble-type sound. It is also staple to be put over a Dubstep wobble-bass.

The limits of filters don't end here. While their function is simple enough, it is in the application of them where they really shine. Try combining a low-pass with a high-pass filter to manually produce a band-pass filter, and in between the two filters you can apply as many effects as you want to produce a truly unique sound. Another tip I would like to mention is to utilize the ADSR envelopes in conjunction with the filters.