Understanding Synthesis: Part 2

Understanding Synthesis

Part 2 Amplitude, Duration and Envelope, Harmonics and Timbre:

Welcome to the second instalment of our blog posts on Sound Synthesis. This month we will be going further into how we can talk about the basics of sound and how we can describe it, this will provide us with the tools we need to talk about shaping the sound as well as creating new sounds.

Sound can also be described through several key properties - Frequency, Pitch, Amplitude, Duration and Envelope, Harmonic and Timbre. We will be focussing on Amplitude, Duration and Envelope, Harmonic and Timbre in this blog post.


This term is used describe the magnitude of the wave in terms of the height of the waveform. In reaktor this will generally work in values +1 and -1 the amplitude affects the perceived loudness of a sound.

Loudness is similar to pitch if pitch is the way in which we perceive frequency then loudness is the way in which we perceive amplitude.

Loudness is how we describe the ordering intensity from Low to high:

Just like pitch, loudness is subjective. What is too loud for one person might be too quiet for another. Loudness is also similar in pitch in that we are sensitive to logarithmic changes instead of linear changes.

For example - two people clapping doesn't feel twice as loud as one person clapping and one hundred people clapping certainly doesn't sound 100 times louder that one person clapping. If it worked that way we would all go deaf everytime a large group of people applauded.

For synthesis we are more interested in how loudness changes over time. Which bring us to duration which is how we order sounds from short to long. Distinguishing between short and long sounds plays a role in how we perceive rhythm. Taking loudness and duration together we can describe the envelope or how the loudness changes over time. We can describe these changes as different stages.

The initial ramp up in loudness is called the Attack this can be thought of as part of the sound that is created when you strike or pluck something.

The ramp down after the peak loudness is called the Decay this can be thought of as the sound decaying away after the initial burst of energy this decay stage can stop at a Sustain level and hold the note out as long as the note is being held out on the instrument. This stage set to a loudness value between 0 and 1 unlike the other stages which are set as a length of time.

The final stage is the final stage is the Release stage which represents the time it takes for a sound to fade to silence after the note is released.

Let's look at some of the Envelopes some various acoustic instruments and see how these loudness curves define the sound.

Longer envelope stages tend to create softer sounds, while shorter envelope settings create punch or plucked sounds.

The envelope is one part that defines a sound. The other aspect is all of the frequencies that make up a sound with the exception of a perfect sine wave, sounds that we hear are made up of multiple frequencies. The lowest frequency in a sound is known as the fundamental which is normally defined as the pitch of the note.

In a pitch sound usually the frequencies above the fundamental are what's called overtones which are also called harmonics. Harmonics are integer multiples of the fundamentals and are found in waveforms such as sawtooths, square waves, triangle waves, trumpet tones, human vowels and any other sound which gives us a strong sense of pitch.

Partials are sine waves that can be inharmonic meaning that they are not integer multiples of any fundamentals. In harmonics partials tend make sounds sound more metallic.

Harmonics are integer multiples of the fundamental frequency. So if the Fundamental of the sound is 440 HZ. The 2nd harmonics would be 880Hs, the 4th harmonic is 1760Hz and the 8th harmonic is 3520Hz. These are all octaves of the fundamental.

Putting together a envelope of a sound and its harmonic content provides us with a way to describe the fingerprint of a sound, this is known as the Timbre of a sound. Timbre is the synthesis of all of these features previously described. Timbre is the way how we describe how one sound is different to another and is typically what we mean when we describe the colour of a sound. Timbre is what allows to distinguish the sound of one sound compared to another and is what we describe when we say a sound is dark, bright, sharp or dull. The art of synthesis is really all about shaping sound using all of these features to make new and interesting sounds.

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