In this article gives a brief introduction to the use of filters and how to apply them to make your instruments a bit more interesting. In general, filters are applied to instruments in EDM music in around four different ways (although you can feel free to correct me if you can think of any I missed). These applications are generally as static, envelope, manual sweep, and LFO (low-frequency oscillator). A static filter - or you could call it “set and forget” - is tweaked to set the tone of the instrument and is left alone throughout the song. An envelope filter is used to control the way the filter behaves when a note is triggered; a manual filter sweep is the recording of a motion of the parameter or knob; and a LFO is a control that cycles the parameter according to a shape such as a sine wave. A few definitions are necessary to begin with.

Fundamental types of filters:

Low pass – A low pass filter cuts all the high frequencies and “only lets the lows pass through”. In other words you can only hear low frequencies coming out of a low pass filter.
Band pass – A band pass filter only lets a certain frequency band pass through the filter. It cuts off all frequencies above and below a certain point either side of the cutoff setting.
High pass – A high pass filter only lets the high frequencies pass through the filter, i.e. you can only hear high frequencies.
Notch – A notch filter is kind of like an inverse band pass filter and removes a certain band of frequencies from the output and leaves the frequencies above and below this point untouched.

Some more complicated filters exist such as the SVF, which is a combination of low pass, band pass and high pass filters. Note that even though it is complex sounding it still comes down to the basic types of filters.

Filters have two controls: cutoff and resonance.

Cutoff – Cutoff is the frequency at which the filter begins. In the case of a low pass filter the cutoff parameter will select the upper frequency that you will be able to hear.

Resonance – Resonance emphasises the frequencies just before those that are reduced in volume. Resonance adjusts how much of that emphasis there is. It makes the filter much more audible and gives it character - it would otherwise sound like just altering the equalisation.

The frequency cutoff control selects at which frequency the filter should start operating and the resonance control creates a peak just before it starts filtering out frequencies.

Static filters

What I’ve called “Set and Forget” filtering is where the filter is used to set the tonal quality of the sound to create an actual instrument. All other frequencies are cut at the frequency set by the filter cutoff parameter. An example of a static filter application is a low-pass filter to create a bass instrument.

Filter envelope

The conventional form for envelopes is ADSR, which stands for Attack, Decay, Sustain and Release. In addition to this the amount, gain or level for the envelope is set. When you play the note the filter cutoff will increase to the value set in the amount parameter at the rate of the attack setting, decrease at the rate of the decay setting and sustain the filter cutoff at the value set by the sustain parameter. When the note is released it will change back to the nominal cutoff value at the rate set in the release parameter. If the amount setting is negative the filter cutoff will decrease with the envelope rather than increase.

Filter sweep

Manual filter sweeps can be done by using the automation tools in your software or by recording motion. This method follows the exact movement specific to that part in the song and is most often used to build tension and the ebb and flow of the tune and to breathe a bit of life into sample-based tunes. A perfect example of this sort of thing is the classic song, “Son of a cheeky boy” by Coma, which is basically just a sample that is tweaked and filtered over a few minutes to make a song. Modern house tracks use this as a matter of formula, like the brilliant “Lola’s theme” by Shapeshifters or the butt-tastic “Call on me” by Eric Prydz. I only mention this here to give a bit of the wider picture as the world of filtering as a production technique. It really is another topic entirely that deserves to be written on its own.

LFO

A LFO, or Low-Frequency Oscillator, is an automated way of performing a filter sweep. A LFO is a control rather than a type of sound. It operates according to a function, such as a sine or triangle wave, and changes the amount of the filter parameter according to the value of the function. So if a sine wave LFO is applied to the filter cutoff, the cutoff will increase and decrease at the same rate of the sine wave. Parameters to be set are usually the rate and amount. LFOs are the functional driver behind vibrato and tremolo effects.

Creative use of envelopes is virtually limitless, and the basic information given here applies to volume envelopes or any other envelope as well. I have included three little samples of songs I have been working on just to give an idea of some filtering envelopes and LFOs on instruments. The three samples use the SVF LP, BP and HP filters found in the standard FL Studio channel settings. The HP sample uses an attack envelope on the cutoff, and the base cutoff value is set in the piano roll differently for some of the notes. The BP sample uses a cutoff LFO and the base cutoff value is set differently in the piano roll for some of the notes. The LP sample uses a LFO on the cutoff and a small attack envelope to give a bit of clarity to when the note is hit, and the notes are pitch bent as they are played.

Related Links

• Virtual Synth Page Glossary
• Cutoff and Resonance Filter FL Studio Help Glossary
• Low Pass Filters on Wikipedia