Using Modulation with a Single Band Filter - Soundtoys FilterFreak

Create Crazy Effects using a Modulator to process a Single Filter Band on a drum beat!

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Filter modulation opens up the world to us sound designers who like to create custom sounds for our mix projects. It is a process that has been in existence since the first decent analogue synthesizers were built but it has always been a step away from reaching producers as a mix colouring tool. That has now changed and more and more producers are realising the power that filter modulation provides in mixing tasks.

To understand how to modulate any parameter of a filter unit one must bite the bullet and swallow some theory and background information on what filters are and how they work.

Filters

A filter allows you to remove unwanted frequencies and also allows you to boost certain frequencies. Which frequencies are removed and which frequencies are left depends on the type of filter you use.

Cut-off frequency

This is the point (frequency) at which the filter begins to filter (block or cut out). The filter will lower the volume of the frequencies above or below the cut-off frequency depending on the type of filter used.

This ‘lowering of the volume of the frequencies,’ is called Attenuation. In the case of a low pass filter, the frequencies above the cut off are attenuated. In the case of a high pass filter, the frequencies below the cut off are attenuated. Put simply: in the case of a low pass filter, we are trying to block the (higher) frequencies above a certain point and allow the lower frequencies through. In the case of a high pass filter, the opposite is true. We try to cut out or block frequencies below a certain point and allow the higher frequencies through.

Analogues use circuitry and for that reason alone, it takes time for the filter to attenuate frequencies, in proportion to the distance from the cut-off point. Today’s technology allows for instant cut-off as the filter attenuation is determined by algorithms as opposed to circuits. That is why the filters off an Arp or Oscar etc, are so much more expressive and warm as they rely completely on the resistors and capacitors to, first warm up, then to work but in a gradual mode(gradual meaning sloped or curved as opposed to instant). Depending on how well a filter attenuates or the way it attenuates gives us an idea of the type of sound we will achieve with an analogue filter.

Slope/Gradient

The speed at which the filter attenuates is called the slope or gradient. Another point to raise now is that you will often see values on the filter knobs on analogue synthesizers that have 12 dB or 24 dB per octave. That basically means that each time the frequency doubles, the filter attenuates by 12 dB or 24 dB everything at that frequency. These are also known as 2 pole or 4 pole filters, each pole represents 6 dB of attenuation. This is how analogue circuits were built, the number of circuits being used by the filter to perform the task at hand.

Resonance

Most synthesizer manufacturers, and in the case of most analogue synthesizers, the term resonance is used most commonly. Other manufacturers of synthesizers, or software synthesizers, might call it emphasis or Q.

Boosting the narrow band of frequencies at the cut-off point is called resonance. If you were to boost the resonance to the maximum, then the filter will begin to self oscillate. This means that it will generate an audible sine wave, more like whistling, even when receiving no input signal.

What is a Modulator

A modulator is a device that controls the parameters of another device. The modulator is called the source and the device being modulated is called the destination. A good and simple example of a source modulator is the pitch wheel on a keyboard and in this instance the destination is pitch. In other words, the pitch wheel when moved alters the pitch of the sound being played.

Almost anything can be a source modulator. Most synthesizer keyboards have a dedicated modwheel (modulation wheel) which can be assigned to a whole host of destination sources and we can replicate this scenario in our DAWs. In fact, we can design our own modulators and have them trigger all manner of processes. We can use Midi controllers to control any desired destination and now we can even use audio to modulate another piece of audio. And it doesn’t end there. Most DAWs give you extensive source modulators to use in the Automation Lanes. In effect, we can use a shape to control the volume of audio.

Modulator Source and Destination

Now that we know what a filter is and how it works we can start to use modulators to control the various features of the filter unit. Common source modulators are LFOs and step sequencers. Common modulator destinations are filter cut-off and resonance. BUT that is only touching the tip of the iceberg. We can use advanced source/destinations to create some crazy textures abut that is dependent on what features the filter unit possesses and whether you want to use additional modulator sources via your DAW’s tools like lane automation.

In the video I use Soundtoys Filter Freak which is a glorified filter unit with acres of control. I explain all the workings of this wonderful plugin and show you how to use the various sources available to modulate the plethora of destinations afforded by this plugin. I cover all the usual filter cut-off modulation tricks, filter resonance modulation madness, step based rhythmic modulation and so on. Every step of every process is explained in detail and using audio examples.

Plugin used in this video:

Soundtoys FilterFreak

Topics covered in this video are:

  • What is a Filter
  • What is Modulation
  • Modes and Types
  • Understanding Q and Width
  • Creative uses
  • Tips and Tricks