Working With Synthesizers - Part II
Part Two: Basic Knowledge – LFOs & Envelopes
In this article series we are going to have a look at synthesizers! We will start with the very basic knowledge and use it then to understand complex sound design, unique workflows and different types of synthesis.
Part two of basic knowledge is about modulation. Modulation means a source, such as envelopes or LFOs, control parameters (for example the cutoff frequency). Instead of doing it all by yourself (via automations or just making the moves with your hands) you can let the machines do the work for you. Isn’t that nice?
LFOs
LFO means Low Frequency Oscillator – and we heard that before! Part One of this article introduced Oscillators as the sound source of a synthesizer. LFOs are no generating sound though, instead they are oscillating slower and therefore cannot be heard. They can modulate parameters by moving them up and down along their waveform. The Modulation of LFOs is looped, which means that as long as a note is played/held the parameter will go up and down with the LFO.
The wave form controls the curve of the modulation. Round sine waves get us to different results than edgy saw waves, while squares switch from 0 to 100 without any movement in between. There are even randomizers, in case you want to go crazy!
The Rate sets the speed of the LFO movement and is usually described by time values such as 1/2, 1/4, …. Because LFO are oscillators the rate can be described in Hz as well. The higher the Hz-value is, the faster the LFO goes. By using the Offset parameter you can change the starting point of the LFO.
There is special cases in modern Synthesizers like Serum where it is possible to create custom LFO waves, instead of using the usual sine, saw, …, which can lead to very interesting results.
LFOs are often mapped to the volume or cutoff frequency, but there is a lot more ways to go here. Using a modern synthesizer that allows free mapping gives you a lot more possibilities to utilize the LFO. What if an LFO would move the Fine Tune of an Oscillator up and down, so the sound changes its pitch in a very subtle way over time? Why not mapping an LFO to the Wave Shape, to constantly change from Saw, to Square and maybe even to Sine?
One of the most important things in making music is letting sounds breath and get them alive. LFOs are one of the most powerful tool to achieve that!
Envelopes 
Envelopes are one-time commands, telling parameters to move the way they want them to. This movement is commonly defined by four parameters: Attack, Decay, Sustain, Release. The curve they build describes the movement of the knob. I called it one-time command because instead of running endlessly like LFOs they are triggered once with every MIDI note.
Attack is the time it takes the envelope to reach the maximum point. Decay sets the time it takes the envelope to fall back again. It does not necessarily fall back to zero, yet the sustain know controls where the envelope goes to after the maximum. The release time comes to action, when the MIDI Note is finished. This is the time it will take the envelope to reach 0 again, in case Sustain is above 0.
If we map an envelope to a parameter, it will start working every time we hit a note. Sometimes there is fixed mappings, such as “Amp Envelopes”, that control the Volume of the synthesizer.
Let’s say our amp envelope has a long attack of 5 seconds. This means that every note starts at zero volume and it takes 5 seconds until the synthesizer has reached the actual volume. Works well for pads, for example! Lead sounds might have shorter attack and decay values because the sound should be pluckier and more defined. Bass Sounds typically have very high sustain, because the sound has to be powerful from start to finish.
But volume is obviously not the only interesting mapping for envelopes. Imagine every time you hit a note the filter opens slightly, allowing more high frequencies to come through. Or the very beginning of every note is pitched up heavily for a very short time. Endless possibilities to explore, especially in synthesizers that allow mapping every single knob, such as Serum.
In the next article about synthesizers we will have a look at the different parts of synthesis like Subtractive, Wavetable and many more!
See you again in the next article!
written by Kos:mo for weltsound.