Using Filters

Filters adjust the frequency spectrum in the sound coming out of the SubTractor's tone generators, and can amplify harmonics as well.

How do they work? As the name suggests, filters stop some sounds from being produced while letting others play. The SubTractor's Filter panel has two tone controls: the Freq (frequency) fader and the Res (resonance) fader (Figure 5.24).

Figure 5.24. The Filter controls

The frequency fader controls the frequency at which harmonic content is cut off. This is sometimes called the cutoff frequency; it can be raised so it doesn't filter out an audible sound, or lowered so it only allows extremely low frequencies through.

By default, anything below the Freq fader position passes through the filter, and anything above the Freq fader position gets cut off. This kind of filter is called a low-pass filter, because low frequencies pass through it and high frequencies are filtered out.

Resonance is the part of the filter that amplifies sound. The Res fader follows the Freq fader and boosts sound at the cutoff frequencyemphasizing harmonics, or resonating. The Res fader has a range from 0 (no boost) to 127 (maximum). At maximum setting, the Res fader will boost certain harmonics so that additional tones get created.

The SubTractor has two low-pass modes that cut off frequencies at different speeds. LP 12 mode fades frequencies gradually (12 dB per octave) and LP 24 fades them more sharply (24 dB per octave). How sharply frequencies cut off has a big effect on how the filters sound when they are resonating. For example, the LP 24 mode has a much more focused, sharp, pronounced resonance than the LP 12. You'll easily be able to hear this for yourself.

The SubTractor also has other types of filters: high-pass, band-pass, and notch.

Filters are more useful when used on tones with a lot of frequency content, such as sawtooth and square waves, and other bright sounds. Filters will have little if any effect on sine and triangle waveforms, which have almost no brightness at all.

Now let's hear what the filters sound like!

To adjust the low-pass filter

1.	Load your test patch.
2.	With your bass loop playing, go to the Filter 1 section and move the Freq fader down to mute the sound (Figure 5.25). Figure 5.25. Nudge the Freq fader down. By itself, the frequency fader may not sound very impressiveit just rolls back high-end, like a "tone knob" that only goes down.
3.	Now increase the Res fader slightly and move the Freq fader back up, to hear the boost in resonance follow the cutoff frequency. With resonance, the filters spring to life and become musical instrumentsno doubt familiar ones you've heard in many different types of music.
4.	Toggle the Filter Type button to LP 24, and repeat steps 2 and 3. Now you should hear how cutoff rate affects the sound of the resonators, as demonstrated by the difference between LP 12 and LP 24 sound. A steeper (24 dB) fade means a more "pointed" resonant boost, resulting in a thinner, more pronounced resonance (Figure 5.26). Figure 5.26. Compare the SubTractor's two low-pass resonant filters. Resonance is the slight bump just before the cutoff frequency.

Tips

• Very high resonance can have unpredictable effects. The SubTractor has a master Level fader located at the far-right of the front panel (Figure 5.27). Nudge it down before maxing out your resonance settings.

  Figure 5.27. The SubTractor's master Level fader

  

  
  

• Filters can provide a lot of drama. Just a little resonance can sometimes turn your little Freq fader into an acid bomb. Try adjusting it as your bass line loopsfilter movements sound great with reverb or delay.

• The high-pass (HP) filter lets higher frequencies through and cuts out those below the Freq fader, or "drops the bottom" out of the tone. As with the low-pass filter, the Res fader boosts frequencies at the cutoff point.

• Pressing Shift while adjusting a fader moves it in one-unit increments.

Now let's try some other filter types.

A band-pass (BP) filter allows only a band of frequencies through, creating a thin spike of sound. With this filter, increasing the Res fader boosts the spike, creating sharp harmonics.

To adjust the band-pass filter

1.	Click the Filter Type button until BP 12 is selected (Figure 5.28). Figure 5.28. Select the band-pass filter type.
2.	With the bass loop playing, boost the Res fader and move the Freq fader up and down for a "lo-fi gizmo" effect (Figure 5.29). Figure 5.29. With band-pass, the frequency fader solos a small frequency band and is good for "lo-fi" effects.

The opposite of the band-pass filter is the notch filter: It drops out a band around the Freq fader, passing everything else through. (Notch has very little audible effect unless it's used in combination with Filter 2.)

With Notch, the Res fader narrows the band as it increases, lessening the effect (Figure 5.30). This can be difficult to hear and is most effective when the Freq fader is moving or when Filter 2 is enhancing the effect.

Figure 5.30. Here's how resonance works on a Notch filter.

To use the notch filter

1.	Play your loop and set Filter 1 to Notch.
2.	To hear how differently the notch filter works, turn Filter 1 resonance up to maximum and move the frequency fader up and down. Remember that the resonance works differently on the notch filter. High resonance means a narrower band being filtered out. The narrower the notch, the less sound gets filtered. The less sound getting filtered, the less noticeable the effect.
3.	Now set the resonance to minimum and move the frequency fader up and down again. Even at low resonance (widest band/ maximum effect), the notch filter is most noticeable when moving, "shimmering" subtly as the frequency shifts.