As you can see the curve is flat in the low register (which means it neither amplifies nor dampens the frequencies in this part of the spectrum) and then, at a certain point, gradually starts falling. When applied to the wave above, this filter cuts away some of the high frequency material in the wave, like this:
Amplitude Amplitude
+
Frequency Frequency
=
FILTER TYPES There are many types of filters, all with their different characteristics and purposes. We will here discuss the three most common types of filters: Lowpass filter The lowpass filter dampens high frequencies and lets low frequencies pass through unaffected, as in the example above. It is the most common synthesizer filter, since it can be used to �round off� the sharp sound of sawtooth waves and pulse waves.
Amplitude Fc (Cutoff Frequency)
Frequency
Highpass filter This is the opposite of the lowpass filter. It lets the high frequencies of the sound pass through and cuts off the low frequencies. This removes �bass� from a sound, without affecting the high end.
Amplitude Fc (Cutoff Frequency)
