The Beginner's Guide to Audio Synthesis

This piece of content originally appeared as a blog post called “The Beginner’s Guide to Audio Synthesis” on the Black Ghost Audio blog.

Overview

A synthesizer is an electronic musical instrument that generates audio signals. These signals can be played back via a set of speakers or recorded into your DAW. Synthesizers come in all shapes, sizes, and price ranges. Most music producers start off using plugin synthesizers, which are third party software that run within your DAW (digital audio workstation).

Synths are used heavily within Pop, EDM, Hip-Hop, and many other genres. Composing music using synth presets is extremely time-effective, but relying too heavily on them can hinder your creative freedom. Being able to efficiently create original synth patches, as well as clone other synths that you hear, is an invaluable asset when collaborating with other artists, and when writing your own songs.

Although its less expensive to start off using plugin synths, as opposed to analog synths, plugin synths tend to come packed with so many controls that it’s overwhelming. You’re faced with a wall of knobs, faders, and miscellaneous controls labelled with complete nonsense. This experience is quite a turn-off and can deter a lot of people from learning synthesis.

Luckily, synthesis can be learned in a systematic, organized manner. Each synth is unique in it’s design and the placement of it’s parameters, but for the most part, they all function based on a standard set of principles and controls. If you understand the fundamentals of synthesis, you can learn how to use pretty much any synth by familiarizing yourself with it’s interface.

Many synths will include an oscillator section, voicing section, envelope section, LFO section, filter section, and effects section. I’ll be walking you through the fundamentals of synthesis using Serum which is a plugin synth developed by Xfer Records. I’ve chosen this synth because it’s one of the most popular synths on the market. You can download a 3 day trial of Serum from Splice for free that will allow you to follow along with this guide. Alternatively, you can buy Serum for $189 via Xfer Record’s website, or you can rent-to-own Serum for $9.99/month via Splice.

An image of Serum by Xfer Records.

Figure 1: Serum by Xfer Records.

This guide is broken down into the following sections:

  1. How to Use a Synth
  2. Oscillators
  3. Voicing
  4. Envelopes
  5. LFOs
  6. Filters
  7. Effects

I hope to familiarize you with the concept of synthesis as a whole and get you comfortable using some of the common parameters found amongst a number of synths. You can always refer back to this guide if you need to refresh yourself on a concept regarding synthesis, so make sure to bookmark this page.

1. How to Use a Synth

To effectively use a synth, you need to understand what makes it tick…. or more accurately: oscillate. A synth is merely a collection of different hardware components packed into a user-friendly unit. Oscillators, envelopes, LFOs, filters, and effects are just some of the components that make up many different synths.

Modular synthesis is a type of synthesis that lets you purchase these components individually and connect them together using patch cables. Many die-hard synth lovers swear by modular synthesis because it provides a ton of creative freedom. Learning how these individual components operate will make using any synth a breeze.

2. Oscillators

The oscillator section of a synth generates waveforms at various amplitudes and frequencies. When creating a new patch, your oscillators are a great place to start. They’ll allow you to achieve the fundamental character of the sound you’re looking for by selecting an appropriate waveform. Lots of synths use basic wave shapes like sine waves, triangle waves, saw waves, and pulse width waves. Others take this a step further and provide you with access to all kinds of different waveshapes.

An image of the oscillator section in Xfer Records' Serum plugin.

Figure 2: Serum’s Oscillator Section.

You can gather more information about the waves you’re using with a spectrum analyzer like SPAN by Voxengo, and an oscilloscope like s(M)exoscope by Smartelectronix (both of which are free to download). A spectrum analyzer displays signal amplitude as it varies by signal frequency, and an oscilloscope displays the waveform of electronic signals by plotting instantaneous signal voltage as a function of time.

A spectrum analyzer is going to display information about the fundamental frequency, as well as its overtones for each of the following waveforms. The term overtone refers to any frequency greater than the fundamental frequency of a sound. A number of these overtones are known as harmonics. If an overtone is a harmonic, it means that it’s part of the fundamental frequency’s harmonic series. A harmonic series is the sequence of sounds in which the frequency of each sound is an integer multiple of the fundamental frequency (the lowest frequency); meaning the fundamental frequency dictates the harmonic series.

A harmonic series with a fundamental frequency of 100 Hz could consist of the following harmonics / overtones:

  • First Harmonic / Fundamental Frequency: 100 Hz
  • Second Harmonic / First Overtone: 200 Hz
  • Third Harmonic / Second Overtone: 300 Hz
  • Fourth Harmonic / Third Overtone: 400 Hz
  • Fifth Harmonic / Fourth Overtone: 500 Hz
  • Sixth Harmonic / Fifth Overtone: 600 Hz
  • Seventh Harmonic / Sixth Overtone: 700 Hz
  • Eighth Harmonic / Seventh Overtone: 800 Hz
  • *A harmonic series can continue beyond eight harmonics.

A harmonic series with a fundamental frequency of 80 Hz could consist of the following harmonics / overtones:

  • First Harmonic / Fundamental Frequency: 80 Hz
  • Second Harmonic / First Overtone: 160 Hz
  • Third Harmonic / Second Overtone: 240 Hz
  • Fourth Harmonic / Third Overtone: 320 Hz
  • Fifth Harmonic / Fourth Overtone: 400 Hz
  • Sixth Harmonic / Fifth Overtone: 480 Hz
  • Seventh Harmonic / Sixth Overtone: 560 Hz
  • Eighth Harmonic / Seventh Overtone: 640 Hz

Each simple waveform that I’ll be covering produces a unique harmonic series, which is what gives each waveform its distinct sound. Some waveforms produce only even harmonics (second harmonic, fourth harmonic, sixth harmonic, etc.), while others produce just odd harmonics (third harmonic, fifth harmonic, seventh harmonic, etc.). Many waveforms produce both even and odd harmonics.

Each even-order harmonic jumps an octave from the last, starting at the fundamental; the result is a harmonious sound. The fundamental frequency will determine the harmonic overtone series. For example, if the fundamental frequency is 100 Hz, it’s even-order harmonics will be 200 Hz, 400 Hz, 600 Hz, 800 Hz, etc. The second-order harmonic is always two times the frequency of the fundamental. The fourth-order harmonic is four times the fundamental. The sixth-order harmonic is six times the fundamental, etc.

Odd-order harmonics tend to sound more dissonant than even-order harmonics based on their relationship to the fundamental frequency; they create intervals with the fundamental that are much more dissonant than the octave jumps created by even-order harmonics.

Instruments like guitar and piano do not produce tones with a pure harmonic series. They create complex tones that contain inharmonic partials; overtones that do not match an ideal harmonic. It can be difficult to determine the overall pitch of a note if these inharmonic partials overpower the fundamental frequency and its harmonic overtones; our brains rely on this information to decipher the pitch of a sound.

Oscillators generate an electrical current (waveform) that repeats continuously unless affected; this waveform can be visually represented using an oscilloscope. An oscilloscope displays the signal amplitude and frequency of a waveform over time. Using an oscilloscope, you can zoom in on a waveform to view a snapshot of it’s wave cycle at varying amplitudes and frequencies.

Sine Waves

Sine waves, or sinusoidal waves, produce a soft, round, warm tone. They’re often used to create sub basses due to how pure they sound; this characteristic translates well in the low-end of many songs.

On a spectrum analyzer, like the one found in FabFilter’s Pro-Q, a pure sine wave will display a fundamental frequency and no overtones.

An image of a sine wave run through FabFilter's Pro-Q 2 plugin.

Figure 3: Sine Wave in a Spectrum Analyzer.

On an oscilloscope, a pure sine wave will have round peaks (mountains) and troughs (valleys). Smooth periodic oscillation is what characterizes a sine wave.

An image of a sine wave run through an oscilloscope.

Figure 4: Sine Wave in an Oscilloscope.

Triangle Waves

Triangle waves produce a tone that’s similar to sine waves, but that has some edge, and fuzz to it. On a spectrum analyzer, a pure triangle wave will display a fundamental frequency and only odd harmonics.

An image of a triangle wave run through FabFilter's Pro-Q 2.

Figure 5: Triangle Wave in a Spectrum Analyzer.

On an oscilloscope, a pure triangle wave looks similar to a sine wave, but it has pointed peaks and troughs.

An image of a triangle wave run through an oscilloscope.

Figure 6: Triangle Wave in an Oscilloscope.

Saw Waves

Saw waves, or sawtooth waves, produce a tone that’s “buzzy” and that sounds somewhat like a trumpet. On a spectrum analyzer, a pure saw wave will display a fundamental frequency with even and odd upper harmonics.

An image of a saw wave run through FabFilter's Pro-Q 2.

Figure 7: Saw Wave in a Spectrum Analyzer.

On an oscilloscope, a pure sawtooth wave typically ramps upwards from the bottom until it reaches the top, and then immediately returns to the bottom again. In reverse, or when the sawtooth wave is inverted, the sawtooth ramps down.

An image of a saw wave run through an oscilloscope.

Figure 8: Saw Wave in an Oscilloscope

An image of an inverted saw wave run through an oscilloscope.

Figure 9: Inverted Saw Wave in an Oscilloscope.

Square Waves

Square waves sound somewhat like a sawtooth wave, but significantly rounder, and fuller. This is due to the lesser presence of odd-order harmonics. On a spectrum analyzer, a pure square wave will display a fundamental frequency and predominantly odd harmonics. A triangle wave contains only odd harmonics, but the higher harmonics roll off much faster than a square wave. Due to the harmonic similarity between square waves and triangles wave, it’s possible to make a square wave sound like a triangle wave using a low-pass filter.

An image of a square wave run through FabFilter's Pro-Q 2.

Figure 10: Square Wave in a Spectrum Analyzer.

On an oscilloscope, a pure square wave will cycle between its peaks and troughs with little to no transition period.

An image of a square wave run through an oscilloscope.

Figure 11: Square Wave in an Oscilloscope.

Pulse Waves

A pulse wave is a type of waveform that includes square waves, and other periodic, but asymmetrical waves. Square waves have a duty cycle of 50%, but that’s not the case for all pulse waves; a half pulse in Sylenth1 has a duty cycle of 75%, whereas a quarter pulse in Sylenth1 has a duty cycle of 87.5%. Pulse waves can sound precisely like square waves (because sometimes they are square waves), or they may take on the sound of a “buzzy” variation of one. On a spectrum analyzer, a pulse wave may look similar to a square wave, but its harmonic structure can differ depending on the wave’s duty cycle.

An image of a pulse wave run through FabFilter's Pro-Q 2.

Figure 12: Pulse Wave in a Spectrum Analyzer.

On an oscilloscope, pulse waves will cycle between their peaks and troughs with little to no transition period.

An image of a half pulse wave run through an oscilloscope.

Figure 13: Half Pulse Wave on an Oscilloscope.

An image of a quarter pulse wave run through an oscilloscope.

Figure 14: Quarter Pulse Wave on an Oscilloscope.

Miscellaneous Waves

Serum is a wavetable synth, which means it’s capable of producing all kinds of waveforms; you can even import images and use them as wavetables. Recreating the sound that a wavetable synth generates can prove difficult due to how many waveforms it’s capable of producing. Most Dubstep synth patches use very complex wavetables, and something like an envelope or LFO is used to modulate throughout the wavetable to create interesting tones.

3. Voicing

Voicing typically refers to the simultaneous vertical placement of notes in relation to each other. From a music theory perspective, voicing refers to how you stack chords.

For example, you could play a C major triad in close position (CEG) with C on the bottom, E in the middle, and G on top. Alternatively, you could play a C major chord in open position, which is a different voicing. To play a C major chord in open position (CGE), you’d move the E up an octave so that the new chord stack contains C on the bottom, G in the middle, and E on top (now an octave higher).

An image of C major in close position.

Figure 15: Voicing #1: C Major in Close Position

An image of C major in open position.

Figure 16: Voicing #2: C Major in Open Position.

The voicing section of a synth generally allows you to control its polyphony; the number of notes that can be played at once. Synths that are monophonic only produce one note at a time (in some cases its one note per oscillator), while synths that are polyphonic produce multiple notes at a time. For a manufacturer to increase polyphony count on an analog synth, it can be quite expensive because it requires them to build more signal paths. If they wanted to expand a synth’s polyphony count from 8 to 16, they would potentially have to double up on a number of the synth’s hardware components.

The Moog One comes in two versions: expensive, and really expensive. I mean… 8-voice ($5,999) and 16-voice ($7,999). The price difference based on the voicing alone is a testament of the expense to the manufacturer (or a unique marketing scheme).

Software synths typically allow for a high polyphony count because the only expense to the manufacturer is the time it takes to program the synth. Serum allows for a polyphony count of up to 32, but a voice count of up to 1088 when both oscillator sections, the sub section, and the noise section are engaged.

An image of the voicing section in Xfer Records' Serum plugin.

Figure 17: Serum’s Voicing Section.

Clearly, voice count refers to something slightly different than polyphony count. In Serum, if you only engage Oscillator A and set the polyphony count to 1, by default, it will produce only one voice. However, if you turn up the Unison amount on Oscillator A, it can produce up to 16 voices on a single MIDI note. You now have a situation where your polyphony count is 1, but your voice count is 16. Detuning Oscillator A’s voices using the Detune knob will make it easier to distinguish the voices from one another.

If you turn up Serum’s polyphony count to 2 and press two notes simultaneously, the total number of potential voices is now 32. The voice count of each section (Oscillator A, Oscillator B, Sub, and Noise) is multiplied by the polyphony count, and those numbers are then all added together to provide a total potential voice count that’s displayed beneath the polyphony count. It’s generally best to set the polyphony count as low as possible to save on CPU. For example, if you’re only going to be playing triads with Serum, you can set the polyphony count to 3; with every section in Serum engaged and all Unison knobs maxed out, that still allows for up to 102 voices.

4. Envelopes

A synth’s envelope section allows you to control amplitude over time. You can set various ADSR (attack, decay, sustain, and release) values to manipulate the amplitude envelope of a sound.

Figure 18: Serum’s Envelope Section.

ADSR can be visualized using a graph that plots amplitude over time. The amplitude of an envelope always starts at zero, rises to a maximum value, drops to a sustained level, and then returns back to zero; this process is controlled using various time values (attack, decay, release), and a single amplitude value (sustain).

An image of amplitude over time. ADSR = Attack, Decay, Sustain, Release

Figure 19: Amplitude Over Time.

In Serum, Envelope 1 controls the synth’s volume envelope. This allows you to shape the volume of Serum’s output over time and decide whether you’d like to create a pluck, pad, lead, etc. When converting a pad into a pluck, manipulating the volume envelope is a good place to start.

Envelopes are not reserved solely for controlling volume; they allow you to control various synth parameters over time. For example, you could map Envelope 1 in Serum to Oscillator A’s Wavetable Position. This would cause Serum to automatically sweep the wavetable position of Oscillator A using the same envelope settings that are controlling its volume. This is an excellent way of making your synths feel “alive.” You could also create an entirely different envelope shape using Envelope 2 or 3 and apply it to various parameters within Serum.

It’s possible to apply an envelope to almost any parameter in Serum by clicking and dragging the crosshair of an envelope to a parameter you’re trying to effect. The setting you drop the crosshair on will have a blue halo appear beside it that you can drag to modify the depth of the envelope’s effect.

Attack

The attack phase of ADSR.

Figure 20: Attack.

Attack time determines how long it takes the envelope to reach maximum amplitude. For a patch that you want to hear as soon as you trigger a note, you’ll want a short attack time for the volume envelope. For a sound like a pad, you may want to use a longer attack time, which would cause it to swell to full volume.

Decay

The decay phase of ADSR.

Figure 21: Decay.

Decay time determines how long it takes for the amplitude to transition from its maximum value to the level set with the sustain knob.

Sustain

The sustain phase of ADSR.

Figure 22: Sustain.

Sustain determines the level at which your amplitude will remain constant after it has attacked, and decayed.

Release

The release phase of ADSR.

Figure 23: Release.

Release time determines how long it takes your sustained amplitude level to diminish to zero once you’ve stopped triggering your synth.

5. LFOs

The LFO (Low-Frequency Oscillator) section of a synth creates a rhythmic pulse or sweep that allows you to control the synth’s parameters over time. LFOs can be applied to parameters in Serum the same way that an envelope can, but the difference is that an LFO isn’t based on ADSR.

An LFO will continuously effect the parameter it’s mapped to, and modulate the parameter based on the shape and rate of the LFO. Typical LFO shapes include sine waves, triangle waves, saw waves, or pulse waves. However, Serum allows you to make custom LFO shapes, which means you aren’t limited in your modulation options.

The LFO section in Xfer Records' Serum plugin.

Figure 24: Serum’s LFO Section.

An LFO is typically used to apply audio effects like vibrato, tremolo, and phasing to your audio signal. If you wanted a filter to open and close every quarter note, you could program Serum to do so using an LFO. LFOs are great for adding texture to your patches and are an excellent way to make your synths come to life.

6. Filters

The filter section of a synth cuts, or in some cases boosts the frequencies of the signal generated by your oscillators. Filters are a fundamental part of subtractive synthesis because they allow you to sculpt the character of your sound.

High Pass

A high-pass filter in FabFilter's Pro-Q 2.

Figure 25: A high pass filter.

A high pass filter passes frequencies that are higher than the cutoff frequency and attenuates frequencies lower than the cutoff frequency. High pass filters are also sometimes referred to as low cut filters.

Low Shelf

A low shelf filter in FabFilter's Pro-Q 2.

Figure 26: A low shelf filter.

A low shelf filter passes all frequencies, but increases or decreases frequencies below the shelf frequency by a specified amount.

Bell

A bell filter in FabFilter's Pro-Q 2.

Figure 27: A bell filter.

A bell filter boosts or attenuates frequencies within a certain range of its center frequency.

Bandpass

A bandpass filter in FabFilter's Pro-Q 2.

Figure 28: A bandpass filter.

A bandpass filter passes frequencies within a certain range of its center frequency and rejects (attenuates) frequencies outside that range.

Notch

A notch filter in FabFilter's Pro-Q 2.

Figure 29: A notch filter.

A notch filter or band-reject filter rejects (attenuates) frequencies within a certain range of its center frequency and passes frequencies outside its range.

Tilt

A tilt filter in FabFilter's Pro-Q 2.

Figure 30: A tilt filter.

A tilt filter boosts frequencies above its center frequency and attenuates frequencies below its center frequency. It can also work oppositely and attenuate frequencies above its center frequency and boost frequencies below its center frequency.

High Shelf

A high shelf filter in FabFilter's Pro-Q 2.

Figure 31: A high shelf filter.

A high shelf filter passes all frequencies, but increases or decreases frequencies below the shelf frequency by a specified amount.

Low Pass

A low pass filter in FabFilter's Pro-Q 2.

Figure 32: A low pass filter.

A low pass filter passes frequencies that are lower than the cutoff frequency and attenuates frequencies higher than the cutoff frequency. Low pass filters are also sometimes referred to as high cut filters.

7. Effects

Synths often come loaded with some effects that you can add into your signal path. Common types of effects include delays, reverbs, choruses, phasers, EQs, compressors, and distortions. I’m not going to dive too heavily into effects because they’re often quite unique to the synth, and some synths don’t even contain effects.

Serum has many effects, and if you like them, you can download a separate plugin from Xfer called Serum FX that allows you to apply Serum’s effects to audio tracks independent of the synth engine. You can find Serum FX in your Xfer account once you’ve purchased a copy of Serum.

The effects section in Xfer Records' Serum.

Figure 33: Serum’s FX Section.

So where should you go from here? Check out “Different Types of Synthesis Explained” for a deeper look at subtractive, additive, wavetable, FM, physical modeling, sample-based, granular, and modular synthesis.