A lowpass filter allows low frequencies to be heard, but blocks the higher
frequencies. It is often used for isolating bass sounds.
A highpass filter allows high frequencies to be heard, but blocks the lower
frequencies. It is frequently used to create hi-pitched whistle sounds, and
piercing synthesizer leads.
A bandpass filter allows the frequencies within a specific range to be heard, and
blocks out all the other frequencies above and below it. It can be used to create a
variety of effects, from the subtle to insane!
A notch filter is the opposite of a bandpass filter – it will block the frequencies
within a set range, and allow all other frequencies above and below it to be
heard. Like the bandpass filter, it can be used to achieve a wide variety of effects.
cutoff Adjust the cutoff of the filter.
Cutoff is used to set the frequency at which the filter’s behavior changes, relative
to the filter type. In a lowpass filter, the cutoff will set the frequency at which the
filter begins to ‘close’ and allow less and less of the higher frequencies through.
When the frequencies are high enough past the cutoff point, no more sound will
be allowed through the filter.
In a highpass filter, the opposite applies – the cutoff sets the frequency point at
which the filter begins to reject sounds that are lower than the cutoff point.
Sounds far enough below the cutoff point will not be let through the filter at all.
In a bandpass or notch filter, the cutoff value acts a little but differently – it sets
the center point of the ‘band’ or ‘notch’, which will taper off as the frequencies
move away from the cutoff point, both in higher or lower frequencies.
reso Adjust the resonance.
Understanding how the cutoff function works is essential to understanding
resonance. In essence, resonance controls the steepness of the ‘slope’ around
the cutoff point. A very steep slope would filter more frequencies sooner, relative
to the sound moving away from the cutoff point. In comparison, a very soft slope
would have the filtering applied more subtly, and require a farther frequency from
the cutoff point to achieve complete signal attenuation.
Steep filter response slopes are referred to as having a higher resonance value,
or sometimes a higher ‘Q’ (which refers to ‘quality’ – a steeper curve is a higher
quality filter because it is more precise).
The slope of a filter’s response curve is often measures in dB/Oct, or ‘Decibels
per Octave’. Values may look like 18dB/Oct, 30dB/Oct, etc. Using 18dB/Oct as
an example, this means that a frequency an octave away from the cutoff point
would be attenuated by 18 decibels relative to the full signal. The higher the
resonance or ‘q’ of the filter, the higher the number in the dB/Oct measurement
will be.
High resonance values will actually add a boost to the frequencies at the cutoff
point, and are useful when you want to really focus on a very precise part of a
sound, or generate intense, cutting tones. Low resonance values are better
suited to subtle and less precise ‘smoothing’ and shaping of your sounds.
drive The Drive knob is used to adjust the amount of signal that is being fed into a
distortion module in Firebird. The higher the value, the greater the effect of the