The Analogue Synthesiser has been a popular instrument for the creation of music for many years. This is a reference as to how the Analogue synthesisers create their sounds.

Origin of the Analogue Synthesiser

The first fully functioning, commercially available Analogue Synthesiser was made by Bob Moog. This was a huge piece of equipment and was very complicated to use. It's appearance resembled old telephone exchanges due to the number of cables that would be hanging out of the various sockets on the front panels. These were necessary because the synthesiser was modular in construction, requiring the user to set up their own sequence through the different parts of the synthesiser. Later synthesiers would be made as an all in one unit which would do away with all the all the cables but offer slightly less versatility but more user friendliness. Analogue Synthesisers are also either monophonic or polyphonic. A monophonic synthesiser would only be able to play one note at a time. A polyphonic synthesiser would be able to play more than one note at a time, which was often as little as 2 notes.

An analogue synthesiser features the following parts:

The Oscillator

The Oscillator controls the pitch and waveform that the synthesiser generated. Sommetimes a synthesiser could have more than one oscillator, so that multiple tones and notes could be generated at the same time.

The waveforms and controls usually available are:

Square/Pulse - This wave switches between it's points of maximum and minimum amplitude almost instantaneously, though it stops for exactly the same duration of time at minimum amplitude as it does at maximum. This produces mellow sound something like you would expect from a clarinet. This is often modulated by a pulse width control which reduces the time spent at maximum amplitude. As pulse width decreases, the sound becomes more buzzy and nasal. Some synthesisers may only have square wave.

Sawtooth - A quite buzzy sound something like you would expect from brass instruments or a violin.

Triangle Wave - A mellow soft sound something like you would expect from sine waves.

White/Pink Noise - Hissing sound such as when you have the radio off tune or your tv with no channel. White noise is a higher frequency than Pink Noise.

Sync - An interesting control found on the oscillators of some synthesisers is the Sync Control. This control keeps the oscillators starting their wave forms at the same time no matter what the pitch. For example: if the wave from Oscillator 1 is 1.5 times as long as the waveform from Oscillator 2, when Oscillator 2 gets halfway through it's second cycle, it will reset to zero and start the cycle again. This can produce some very unusual, complex waveforms resulting in very unusual sounds.

The Filter

The filter allows the removal of certain frequencies of the sounds generated by the oscillator to create different tone qualities.
The filter was often able to be switched between varying types, these are:

Low Pass Filter - This reduces mid to high frequencies from sounds. This is the most common type of filter found on Analogue Synthesisers.

Band Pass Filter - This reduces high and low frequencies from sound. This filter was less commonly found on synthesisers. Usually results in the sounds being rather nasal in tone.

High Pass Filter - This reduces middle and low frequencies from the sound. This was often helpful in making a sound very sharp but with no bass frequencies. This was considerably more common than the band pass filter

Band Stop - which removes the middle frequencies from a sound. A very rare filter which is mostly exclusive to the modular synthesiser.

Cutoff Frequency

This control determines the point at which frequencies are cut from the sound. An example of the effect produced by reducing the cutoff frequency can be done without need for any synthesisers, merely try making a hissing sound with your mouth wide then reducing your mouth to a shape more appropriate for whistling. This would produce a sound something like tssseooowww. Which is how the cutoff frequency affects things.

Resonance

Another control which affects the filter is resonance, though it is sometimes known as Q or Peak. The example above, of how you can emulate reducing the filter in realtime, gives a sound that is more akin to this action being done when there is some resonance aplied to the filter. It makes the sound more spectactular (especially when the filter is being modulated in some way such as in the above example) by emphasis of certain harmonics and frequencies within the waveform.
A sound with resonance applied is typified by it's more 'weowingieowing' sound than the more 'zzzeeewwwweeeezzz' of a sound without resonance.

Envelope Generator

This part of a synthesiser is used mainly for controlling the contour of the volume of the sound. The exact contour is determined by the following controls:

Attack - This is how quickly the sound builds to maximum volume. A short attack value is good for percussive or plucking style sounds (like for instance a piano). A slightly longer would be more like quick bowing or blowing of an instrument (like trumpet or quick violin work). Long attack times are mainly like that of a slow bowing of such as a violin.

Decay - This is how quickly the sound decreases to it's minimum volume whilst the key is held. A sound such as a violin would tend to have a quick decay whereas a piano would tend to have a longer decay.

Sustain - This determines a point at which the sound would stop decreasing in volume and be held until the key is released. If the sustain is set to a value less than maximum the effect might sound like if a violin had been quickly bowed but then the player continues the stroke slower.

Release - This is how long the sound lasts after the key has been released. It works like the decay but after sustain and without the requirement to hold the key on the synthesiser.

The envelope generator isn't always just used for controlling the contour of the sound. With modular synthesisers it is possible to have many envelope generators which can be linked to many parts of the synthesiser such as the pulse with or pitch.

With the all in one synthesisers, a control is often found on the
filter called 'EG Depth' (which stands for Envelope Generator Depth) and controls how much the Envelope Generator is able to vary the cutoff frequency. Low settings of this would cause little effect, whereas large settings would have massive effect. Some synthesisers have more than one envelope generator. A second envelope generator is usually found on the filter to allow it to be modulated independantly of the volume of the sound.

Another interesting aspect of the envelope generator is the control to reverse the envelope. This however was rarely applied to the volume. It was more often applied to the filter. As such attack would control how rapidly a sound would reduce to it's minimum cutoff level and such as decay and release would determine how quickly it rises again to it's maximum. Sustain would affect the point through the decay process that the sound is held whilst holding the key.

Low Frequency Oscillator (LFO)

This works in a similar way to an Oscillator but at much lower frequencies. The LFO is designed to function purely to modulate other parts of a synthesiser. On most synthesisers it is able to affect the pitch, cutoff fequency, pulse width or output volume. The amount of affect the LFO has on any particular parts of a synthesiser is altered via the control MOD Depth. There is a separate control for each section on each part the sythesiser than can be affected. The filter usually has the same waveforms as an oscillator only with a couple of additions. These are:

Ramp - This is like the sawtooth waveform, only in reverse. Instead of starting and maximum and decaying, it starts at minum value and rises.

Sample and Hold - Very similar in some respects to White and Pink noise as it's output is random. What this actually does is take a sample from a random signal and holds that value until it is triggered to do so again. The rate at wich the samples are taken is dependant on the frequency the LFO is set to. Applying this effect to the pitch creates an effect I'm sure most of us have heard at some point in some sci-fi movie as it has often been used to represent the sound of a computer.

Ring Modulator

This isn't found on that many synthesisers but is a fascinating and rather odd device. What it would do is multiply the frequencies that are fed into it from 2 oscillators and then provides an output that is the sum and difference of the two frequencies. The end result of this is that the tone comes out as a very metalic sound. A ring modulator was used to create the Dalek voices on Dr. Who.

Performance Enhancers

To add extra expression to live performance sockets were added for footpedals to be connected to control such as volume or cutoff frequency. Later synthesisers could often have keyboards which could affect the cutoff and volume by how fast you hit the keys (velocity sensitivity and how much pressure you applied afterwards (aftertouch). This isn't exclusive to analogue synthesisers however. There would often be a wheel control for controlling LFO modulation of pitch or cutoff frequency or a wheel controll for controlling the pitch or cutoff directly. Sometimes synthesisers had both.

Arpeggiator

This is a device which allowed users to hold down several notes but intead of the synthesier playing the entire them all, it would cycle through the notes that are being held. It would often be possible to set it to cycle through several octaves. As such it was possible to hold one note and have the synthesiser automatically jumping between octaves. This effect was extremely popular and can be heard on many synthesiser records from the 1980s. The arpeggiator usually had a control to vary it's speed or it was controlled by the LFO Frequency. It was also possible to set how the synthesiser would cycle the notes:

Up - This would start at the lowest note and cycle to the highest and then repeat

Down - This starts at the highest note and cycles to the lowest then repeats

Up and Down - This would cycle from the lowest note up to the highest then back down again. Exactly how it did this varied depending on the synthesiser. Some synthesisers would play the top and bottom notes twice. For example if C E and G were held the sequence would go C E G G E C then repeat.

Random - Randomly cycles through the notes being held and randomly cycles through the ocataves should it be set to cycle through octaves

As Pressed - This would cycle through the notes in the order that they were pressed. If octave cycling was set then it was most common for the octaves to cyle up and then repeat. This can be heard to great effect on Dreams of Living by The Human League.

Sequencer

This would be able to produce a sequence of notes and/or a series of modulations to another part of the synthesiser. The analogue synthesiser would be a series of knobs that would be set to various positions to produce the required effect. These were usually limited to 16 events. Whereas a Digital sequencer would be one which would remember a sequence of notes that were played. The most famous one is on the Roland SH-101 synthesiser which features a 100 note digital sequencer. The sequencer on the SH-101 was independant of the keyboard so as soon as play was selected the sequence would play. Analogue sequncers generally depended on a key being pressed and would play different pitches depending on the key pressed.

...Then The Fireworks!

Chorus - The most common effect found on analogue synthesisers. Most commonly found on the polyphonic synthesisers. Adds an extra warmth and sparkle to the sound similar to the effect created by a 12 string guitar.

Flanging - Less common than chorus but still found on a quite a few synths. This tends to create a sound something like it was being played down a drainpipe. Flaning can be set to cycle like with an LFO or it can be fixed at a certain effect. Whether you can do this depends on the synthesiser. The ability to modify the flanging is usually only available on the modular synthesiser

Phasing - Less common an effect and mainly found on the modular synthesisers. This is an undulating whooshy swirling type sound.

Delay - Effectively this is the sound being repeated at lower volumes (and sometimes clarity) as if being echoed.

Reverb - This would add extra dimension to the sound as if it were being listened to with a certain acoustic such as for example a large hall.

And that's what you're likely to find on an Analogue Synthesiser!