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There are a lot of great virtual instruments (VIs) available for composers these days. Most of these include an impressive array of presets that sound great and provide good sounding results with very little work. Many of us don’t have the time or desire to design sounds from scratch, even though most VIs offer tremendous sound sculpting capability. But using presets all the time can lead to homogeneous sounding music. With a little understanding of what the knobs, sliders and drop down menus on the interface control, it is easy to tweak the sounds to make them your own.

Many of the parameters and terminology that VIs use for sound modification have their roots in analog synthesis. Understanding the terminology and the parameters they control will help you better understand how to get the sonic results that you want. Let’s break down some of the terminology and parameters you will encounter on many VIs.

An oscillator is an electronic waveform that serves as the sound source for a synthesized sound and is abbreviated as OSC. No oscillator, no sound. These waveforms are usually sawtooth, square, sine or triangle waves and are distinguished from each other by their harmonic content. A sampled sound source is not considered an oscillator but it functions in the same basic way. It is the genesis of the preset’s sound and can be manipulated in a variety of ways.

Sound sources can be swapped or changed quite easily in most VIs. They are generally changed via a dial or a drop down menu in the VI’s interface. In Omnisphere, for example, clicking on the sample window in any layer will allow you to choose from thousands of soundsource samples, greatly expanding the sonic possibilities of the instrument with a single click. Changing the oscillator or sampled waveform is the most basic way of changing the sound.

A filter is a tone control. Most VIs include a low pass filter (LPF) and a high pass filter (HPF) to allow you to shape the frequency content of your sound. They may also include a band pass filter (BPF) which allows you to target a specific frequency band. If your sound has too much high frequency content, lowering the cutoff of the low pass filter will make it sound less bright. A sound that is too bassy can be thinned out by changing the cutoff of the high pass filter. The treble and bass controls on your stereo are examples of low and high pass filters that you are probably already familiar with.

Filters also include a resonance control, abbreviated as RES. The resonance control increases the intensity or volume of the frequency at the point of the filter cutoff. A high amount of resonance applied to a low pass filter is used to achieve the barking or squelchy sound heard on many synth sounds.

Envelopes are used to control the volume (amplitude envelope) or frequency (filter envelope) contour of a sound. They change the sound over time. Envelopes have stages to control the sound at various points in time. They are expressed as attack, decay, sustain and release and abbreviated as ADSR. Whenever you see the letters ADSR, you can be sure that that is an envelope.

On an amplitude envelope, the attack value determines how quickly the sound increases in volume from silence. A percussive sound has a very fast attack, whereas a legato sound has a slower attack. Decay controls how fast the sound lowers in volume to its sustain level and the release value determines how long it takes the sound to fade out after the note ends when the keyboard’s key is released. The envelope is often the first aspect of the sound you wish to tweak, so knowing where to find it is very useful.

Modulation and LFOs
LFO stands for low frequency oscillator LFOs used to change aspects of the sound in a repetitive or cyclical fashion. An LFO uses a waveform such as a sine or square to modulate a parameter. It is called a low frequency oscillator because it oscillates or cycles below the range of human hearing. Human hearing extends down to 20 Hz, so any waveform below that is inaudible and can be used as modulator.

The speed of the LFO determines how fast the parameter is being modulated. On most VI’s, the LFO can be synced to the tempo of the DAW’s session. Common parameters to modulate are volume, panning, pitch, filter cutoffs and resonance. If I use an LFO to modulate the volume of a sound I can create a tremolo effect. If I use an LFO to modulate pitch, I can create vibrato.

LFOs are great for generating sonic variety because static sounds become boring to the ear. When a cellist plays, he makes slight variations in the timbre, pitch and volume of the note, even when playing held notes. Synthesizer and samples don’t do this unless you use a modifier such as LFO to give the note some variety.

Many VIs have tremendous modulation capabilities, allowing the user to manipulate virtually any parameter with an LFO or envelope. These modulators are the basis for many of the complex changing sounds we hear in VI’s like Omnisphere, Massive or Absynth. In fact, a great way to learn more about your VI, and synthesis in general, is to deconstruct one these complex sounds.

All the functions I have mentioned so far are found in the VI itself, so they require bringing up the VI’s interface and manipulating a virtual knob or slider to change the sound. But we can also change the sound of a VI from the DAW itself. The best way to do this is with a MIDI continuous controller.

Continuous Controllers
Most electronic musicians are aware that you can change the volume of a sound in real time by using a MIDI volume message. The MIDI parameter that changes volume is a continuous controller, in this case, MIDI CC7. Your MIDI controller might have faders built in to it that are assigned to send MIDI continuous controller messages. Continuous controllers can be used to automate many parameters in VIs.

VI manufacturers usually program their sounds to respond to specific MIDI continuous controllers to give additional expressive capabilities, so make sure you peruse your manual to find out what MIDI CCs your synth or sample libraries have already been programmed to respond to. String libraries are often programmed so that if you move your modulation wheel, which sends out MIDI CC1, the sound will change in dynamic intensity.

Most VIs have a MIDI learn capability which allows you to assign a MIDI CC of your choosing to any parameter on the instrument. A common way of implementing this is by having you control click on the parameter you wish to automate, selecting MIDI learn and moving the knob or fader on your MIDI keyboard or controller that you wish to use to automate the parameter. I recommend setting the faders or knobs to send the MIDI CC of your choosing on your keyboard’s interface. Just make sure that the one you are learning on your VI is not being used to automate something else. For this reason, you should avoid MIDI continuous controllers such as 1 (modulation), 2 (breath), 7 (volume), 10 (panning) and 11 (expression) to customize your, as these have usually already been assigned.

The parameter that is now automated via MIDI will be effected by moving the assigned fader. You can record those movements as you play a part or draw them in to the sequence with your mouse. Assigning and using continuous controllers is one of the best ways of getting greater expressiveness out of your VIs.

A little knowledge of the common parameters used on VIs goes a long way to helping you shape the sounds more to your liking. You may never wish to program VIs from scratch, but at least you can tweak them so they represent more of what you wish to hear. I always recommend reading the manuals, viewing the manufacturer’s tutorial videos and checking online forums to further your knowledge of an instruments’ specifics. However, VIs share more similarities than differences, so a firm grasp of the commonalities can take you pretty far.

Originally published in THE SCORE magazine Vol. XXIX No. ONE