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Synthesizers

November 15, 2017

Synthesizers have come a long way since their use within pop music in the 1960s and wider adoption in the 80’s and from listening to the current top 50 music charts you still can hear their influence and use within a variety of different songs. Thinking back over the last few decades it’s impossible to imagine a world without synthesizers, they have become synonymous with certain eras, bands and even defined music genres such as; Trance, House or Dubstep.

 

What exactly is a synthesizer, what are its common features and how do they work?

 

This sequence of blog will shed light on these three questions and should give you a better understanding of how to use them for your own musical compositions. So let’s start by defining what a synthesizers is, I find this description useful:

 

“A synthesizer (often abbreviated as synth, also spelled synthesiser) is an electronic musical instrument that generates electric signals that are converted to sound through instrument amplifiers and loudspeakers or headphones. Synthesizers may either imitate traditional musical instruments like piano, Hammond organ, flute, vocals; natural sounds like ocean waves, etc; or generate novel electronic timbres. They are often played with a musical keyboard, but they can be controlled via a variety of other input devices, including music sequencers, instrument controllers, fingerboards, guitar synthesizers, wind controllers, and electronic drums“

 

There are many different types of synthesizers: hardware, software, digital etc. Many of them differ in the ways that they create and shape a sound (something that will be covered in the next blog) however they all tend to share common, basic features and signal flows. If you can understand this then you are on course to being able to create the sounds you want from your synthesizer. So without further ado, The most common features of a synthesizer are:

 

Oscillator

 

An oscillator is the sound generating section of a synth and is at the start of its signal chain. Within hardware synths a circuit converts DC power into an AC signal that fluctuates according to a particular pattern a given number of times per second, this pattern is the waveform. Within software synths digital oscillators are electronic oscillating signals generated by computer digital signal processing.

Whether you use analogue or digital synths, the type of waveform selected will always be the raw material used to create the character of your sound, it can be seen as the key ingredient of your musical dish that provides the main flavouring. Some synths have more than one oscillator built into them and multiple waves forms to select from however I have decided to focus on the the most commonly found waveform types:

 

Sine wave: The wave looks like an s placed horizontally, it has the softest sound out of all the waveforms and contains the least harmonics resulting in a mild sound. 

 

Triangle wave: The wave generated looks like a triangle sequentially facing up and down. It’s softer sounding than the square and saw waves with less harmonic content.

 

Square wave: The wave generated looks like near perfect square, facing up and down sequentially. Its sound is more hollow than a saw wave.

 

Saw wave: The wave generated looks like the teeth of a saw blade and the sound is full bodied with rich harmonics.

 

ADSR envelope generator

 

A,D,S,R stands for: Attack, Decay, Sustain & Release. This part of a synth takes the signal and controls how it performs over time. For example it can be used to control how long the sound takes to start and reach an amplitude level - its Attack, then controls how long it takes to Decay from this level to reach a sustain point, from here a sound can be Sustained as long as a user would like and once the user has stopped the sustain of a sound the Release setting controls how long the sounds takes to fade from sustain to zero amplitude.

This description of an ADSR envelope has been applied to control the volume of sound but can be applied to other features of a synth such as controlling how it’s filter operates over time.

Filter

 

A filter is a part of a synth that allows you to alter the frequency content of waveforms generated by oscillators. They typically allow you to remove frequencies by using different filters types.

Common filters found on synths are; low pass filters, like the name suggests they only allow the low frequencies to pass through at a user selected frequency creating a less bright, duller sound. A high pass filter which only allows high frequencies of an oscillator through at a user selected frequency. Band pass filters are a combination of a low and high pass filter, resulting in a narrow band of frequencies to pass through the synth helping isolate a specific band of frequencies to be used. A band reject/stop filter is the opposite of a band pass filter and filters out a narrow band of frequencies allowing the low and high frequencies either side of it to pass through.

 

 

Some filter sections contain something called resonance or Q. Resonance occurs when sound in the pass band near the cutoff frequency is sent back into the filter as it comes out, creating feedback. The amount of feedback affects the volume of these frequencies, as well as the timbre of the sound, essentially the Resonance/Q increase in amplitude of frequencies close to the cut off for a filter. (pictures)

 

LFO (Low frequency Oscillator)

 

An LFO is an oscillator that operates at a very low, sub audio frequency, it gives out a slowly oscillating signal. The LFO can be any waveform, with a user set volume and is often used to affect other sections of a synth. A common use of an LFO is to route it to a low pass filter so that it will open and close quickly, a trick used in countless Dubstep tracks.

 

Effects

 

Some synths have built in effect units that you can sent your oscillated signal to. Some of these effects might be a chorus which sounds like the doubling up of your sound, a reverb or a delay effect.

 

Keyboard

 

Although not always found on every synthesizer a keyboard is often built into a hardware synth to turn on sounds and trigger different pitches. Midi controllers are often used to operate software synths found on computers.

 

Hopefully you should now have a better understanding of what a synthesizer is and it’s common features. The next blog will look three common types of synthesis: Subtractive, FM and Wavetable.

 

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