How Additive Synthesis Works

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Additive synthesis is a key method in sound synthesis (learn more). It’s a detailed and strong technique that can create rich sound environments.

The main idea is to layer sine waves together. Each wave is carefully adjusted to certain frequencies and volumes, to build a final sound.

This careful layering is controlled by Fourier’s theorem. It lets you make a wide range of sounds by changing the parts that make up the sound’s pitch and tone. It can be used in different types of music and situations.

In this guide, you’ll learn all about how additive synthesis works, it’s best use-cases and more.

Fundamentals of Additive Synthesis

Additive synthesis is a sound design technique that is like crafting sounds with building blocks.

It starts with the most basic form of sound called sine waves. Each wave is like a single note in a big, complex sound picture. By changing how fast these waves move, sound designers can make all sorts of sounds.

They can create the soft sound of a flute or the sharp sound of a synthetic lead. Additive synthesis, which relies on changing the speed and loudness of waves, gives a lot of room for creativity in sound design.

How it Works

Additive synthesis is a sound synthesis technique that creates timbre (character and tone) by adding different sine waves together.

The timbre of any sound can be represented as a series of numbers, and additive synthesis recreates this series to generate the same timbre.

Each sine wave, called a partial or harmonic, has its own frequency and amplitude.

The user can control the number of partials, their frequencies, and their amplitudes to create a desired sound.

For example, to recreate the sound of a flute, the synthesizer must generate several sine waves with specific frequencies and amplitudes. The user can manipulate these parameters until the desired sound is achieved.

In a digital synthesizer, this process could involve using a Fourier transform, which breaks down a complex wave into its individual sine waves. The synthesizer then adds these waves together to create the final sound.

Joseph Fourier Picture
Joseph Fourier

Fourier What???

Fourier’s Theorem is like a recipe to make a fancy dish. Imagine you have a really complex dish, like a big, fancy layered cake. It’s hard to understand what’s in the cake if you just look at the whole thing, right?

But what if we could break the cake down into its individual ingredients? Like flour, eggs, sugar, butter and so on. That makes it a lot easier to understand the cake.

Fourier’s Theorem does something similar, but with wavy lines or signals. It says you can take any complex signal and break it down into simple sine and cosine waves.

These are the “ingredients” (i.e. partials/harmonics) of the signal.

Note: just like how a cake is more than just flour or eggs, a signal is more than just its individual sine and cosine waves. But breaking it down can make it easier to understand and work with.

The Fourier Transform is like the chef that knows exactly how to break down the cake into its ingredients. It’s a mathematical method that applies Fourier’s Theorem to a signal.

So, if you give the Fourier Transform a signal, it can tell you what sine and cosine waves make up that signal.

And with that, you can then use additive synthesis to create whatever sound you’re looking for.

Intro to Harmonics and Sound Sculpting

Additive synthesis is all about playing with two things: frequency and amplitude. Think of these as the sound’s pitch and volume. By tweaking these, you can create all kinds of sounds.

One of the cool things about additive synthesis is the ability to play with harmonics.

These are parts of the sound wave that can change how a sound feels. By adjusting the strength and presence of these harmonics, you can control the sound’s character. You can make it feel warm and soft or sharp and piercing.

You can also change the loudness of these harmonics over time. This is called amplitude shaping, and it’s great for making sounds feel more real.

If you’ve ever listened to a real musical instrument, you know the sound doesn’t stay the same. It has an attack (start), decay (drop), sustain (hold), and release (end). Amplitude shaping lets you mimic this natural pattern.

Further, by changing the pitch of different harmonics, you can create effects like vibrato and tremolo. These add depth and character to the sound.

Techniques and Sound Design

In additive synthesis you can control the tone of the sound with great detail since you’re controlling individual sine waves that are stacked together.

Let’s take a closer look at the different sound sculpting methods you can employ with additive synthesis.

Frequency Modulation in Additive Synthesis

You can also utilize techniques like frequency modulation with additive synthesis, where you can make sounds that change and move over time. This adds depth to music.

An example of using FM with additive synthesis could be creating a complex musical tone. First, in additive synthesis, multiple sine waves with different frequencies and amplitudes are added together to generate a unique sound. This could produce a rich harmonic tone.

Then, frequency modulation could be applied by using a “modulating signal” to alter how the original sound (the “carrier signal”) plays back. The newly created complex waveform could be used as the carrier, and another waveform as the modulator.

By dynamically changing the frequency of the carrier with the modulator, one can introduce vibrato, tremolo, or other frequency-based effects to the sound.

Envelope Shaping in Additive Synthesis

Envelope shaping is also a key part of additive synthesis. It lets you control how a sound starts, gets louder, stays steady, and ends. This is called the attack, decay, sustain, and release (ADSR envelope). You can adjust each wave to mimic real-life sounds or make new, alien-like sounds.

  1. Attack: This is the phase where the sound starts and builds up to its peak. The rate of this build-up can be controlled to create either an abrupt or gradual start to the sound.
  2. Decay: After peaking, the sound starts to decrease in this phase to a level determined by the sustain stage. This falling action can be rapid or slow, affecting the sound’s character.
  3. Sustain: This stage refers to the steady state of the sound after the decay. It continues until the sound is stopped. The level maintained during this phase will have a significant impact on the overall feel of the sound.
  4. Release: This is the final phase where the sound gradually fades away after being stopped. The length of this phase can be adjusted to create either a sudden stop or a prolonged fade out.
ADSR Envelope Diagram

We create a specific sound by modulating the amplitude or intensity of individual harmonics over time. By manipulating the four stages of the envelope, you can shape the dynamics of the sound produced in additive synthesis.

For example, a piano sound has a fast attack and decay, while a violin sound has a slower attack and longer sustain and release.

Harmonic Control in Additive Synthesis

You can also control the harmonics in additive synthesis. This means you can make sounds louder or softer. You can create a wide range of tones, from simple to complex. You can also control how bright or warm the sound is.

Each of the individual sine waves used when designing a sound is referred to as a harmonic.

For example, if we want to create the sound of a violin, we would start with a fundamental frequency, say, 440 Hz (which corresponds to the A4 note on a piano). This is the perceived pitch of the sound.

Next, we would add harmonics to this fundamental frequency. The first harmonic would be at twice the frequency of the fundamental (880 Hz), the second harmonic at three times the frequency (1320 Hz), and so on.

To accurately recreate the sound of a violin, we would adjust the amplitude (volume) and phase (timing) of each of these harmonics.

For instance, the odd-numbered harmonics (3rd, 5th, 7th, etc.) might be quieter than the even-numbered ones. Also, some harmonics might start slightly later than others, creating a “bowing” effect.

By precisely controlling these harmonics, we would be able to mimic the rich, complex sound of a real violin using additive synthesis.

Amplitude Modulation in Additive Synthesis

Amplitude modulation is also important. It lets you change how loud the waves are. This can make it sound like a tremolo or vibrato effect. It can also add a pulsing quality to the sound. This makes the sound experience even better.

An example of amplitude modulation could be the creation of a “tremolo” effect.

To create a tremolo effect, two sine waves are needed: one is a low-frequency oscillator (LFO), and the other is the primary frequency of the sound.

The amplitude of the primary frequency is then modulated by the LFO.

For instance, if the primary frequency is 440Hz (which corresponds to the pitch of the note A4) and the LFO is 5Hz, the amplitude of the 440Hz wave will increase and decrease 5 times per second, creating a pulsing tremolo effect.

The depth of the tremolo effect can be controlled by adjusting the amplitude of the LFO. The higher the amplitude of the LFO, the more dramatic the volume fluctuations of the primary sound will be.

Practical Usage and Tips

To use additive synthesis well, you should start simple. Begin with playing around with a basic sine wave. As you get the hang of it, start adding more complex structures.

This slow and steady way helps you understand how different sounds, known as timbres, are made using this technique. Once you’re confident, you can start experimenting more and use these skills in your music production.

Programming a synth for additive synthesis needs careful attention to detail.

By adjusting the volume of each harmonic, you can change the sound drastically. This gives sound designers the chance to create unique sounds that are hard to make using other techniques.

Keep playing with the harmonics to discover a whole world of sound.

To use additive synthesis in the real world, start with easy sounds and slowly add complexity. This helps you understand how each harmonic changes the final sound.

Here are the fundamental waves you can use in additive synthesis:

  1. Sine Waves: These are the simplest type of sound waves where the wave flows smoothly, producing a pure and clear sound. It’s the fundamental building block in additive synthesis.
  2. Square Waves: These waves produce a hollow, reedy sound. Square waves are essentially a collection of odd harmonics, which can be combined using additive synthesis to create a square wave effect.
  3. Sawtooth Waves: These waves generate a bright and buzzy sound. They contain both odd and even harmonics, and are a common choice for synthesizing brass and string sounds.
  4. Triangle Waves: These waves create a sound that is more mellow and less harsh than the square or sawtooth waves. They are closer to a sine wave in terms of harmonic content, containing only odd harmonics.

Here are some common uses for additive synthesis for your sound design and music production:

  1. Noise: This is not a specific waveform but a random signal that contains all kinds of frequencies. In additive synthesis, noise can be used to add a percussive or breathy quality to the sound.
  2. Bell Sounds: By combining sine waves of different frequencies and amplitudes, you can create complex sounds such as the sound of a bell or a gong.
  3. Organ Sounds: This is achieved by adding multiple sine waves, each one representing a different pipe of the organ. The individual sine waves are often referred to as “drawbars.”
  4. String Sounds: Additive synthesis can be used to create the sounds of plucked or bowed string instruments by combining various harmonics and adjusting their decay times.
  5. Wind Instrument Sounds: By carefully controlling the harmonic content and the attack, decay, sustain, and release (ADSR) envelope, additive synthesis can be used to create realistic sounding wind instruments.

Popular Additive Synths

Here are some of the popular additive synths out there in the market today:

Native Instruments Razor Additive Synth Screenshot
  1. NI Razor: Native Instruments’ Razor is a powerful additive synthesizer that uses up to 320 partials to generate a sound, allowing users to manipulate the sound in real time. It is known for its unique and complex sound design capabilities.
  2. VirSyn CUBE: CUBE is an additive synthesizer that can generate a nearly infinite range of sounds. It has a morphing feature that allows users to create a smooth transition between different sounds.
  3. Image Line Harmor: Harmor is a fully-featured additive synthesizer that provides two separate engines for creating complex sounds. It includes image synthesis, allowing you to create sounds from pictures, and advanced resynthesis capabilities.
  4. Loom II by AIR Music Technology: This is an upgrade from the original Loom modular additive synthesizer. Loom II offers 8 voices, a spectral noise section, and a randomizer feature that can generate unique sounds with the push of a button.
  5. PPG Wavegenerator: This synth, by Wolfgang Palm, is an innovative and flexible additive synthesizer. It enables the creation of waveforms through the combination of sine waves, and offers a unique visualization of wave shaping and modulation.

Additive Synthesis Today and Tomorrow

Sound design has come a long way. The old methods laid the groundwork for great sounds. But, today’s additive synthesis, or sound creation, is getting even better with the help of new tech and ideas. This is changing the sound of modern music.

New technology lets today’s synthesizers use hundreds of sound waves.

This lets music makers create sounds with great detail and complexity. Some software use complex math, like Fast Fourier Transform, to take apart and put back together sound signals. This makes the sounds of additive synthesis even more creative.

Also, each sound wave can be changed and moved around. This makes the sounds even more exciting and changing. It can create all kinds of sounds, from soft pads to complex rhythms. Today’s additive synthesis combines old principles and new methods. It keeps pushing the limits of sound design.

Additive synthesis is used a lot in digital audio workstations (DAWs). These tools make it easier to create complex sounds. This means more artists and music makers can use this technique.

What does the future of additive synthesis look like over the next 10 years?

  1. More Advanced Software: With the rapid advancement in digital technology, software for additive synthesis is expected to become more sophisticated, user-friendly, and capable of generating a wider range of sounds with better quality and efficiency.
  2. Artificial Intelligence Integration: AI will likely play a significant role in the development of additive synthesis. It might be used to automate the creation of complex waveforms, making the process easier and faster for musicians.
  3. Virtual Reality and Augmented Reality: With the rise of VR and AR technologies, there may be new, more immersive ways to interact with additive synthesis, potentially leading to new forms of music creation and performance.
  4. Accessible Hardware: As technology continues to become cheaper and more accessible, we could see an increase in the availability of hardware specifically designed for additive synthesis, bringing it into more studios and homes.
  5. Education and Research: As additive synthesis becomes more accessible and widely used, there will likely be an increase in education and research focused on it. This could lead to new techniques and technologies, further pushing the boundaries of what’s possible.

Overall, the future of additive synthesis looks promising and exciting, with many technological advancements on the horizon.

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