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Synth Vocab

SYSTEM: electronics/Technical terms/explain/full readout/graphics/buzzwords FILE FOUND: vocab engineer/Andy Honeybone


Can you be arrested when you sample and hold? Is ring modulation physically damaging or the result of a heavy breakfast? These questions and others are answered in our dictionary of synthesizer terms. Follow the OTT guides ('orrible technical thingies) along the cartoon circuit and emerge a wise man.

FACILITIES



Arpeggiator: A bonus of using a microprocessor to control a keyboard is that it can either assign the top or bottom member of a group of notes to a single oscillator or, if so programmed, step through that group at a rate usually set by the LFO. This effect can be used to "strum" chords on a monophonic synthesiser.

Envelope generator: Each sound has its own shape, which for example might be a short attack, a medium sustain in the middle then a gradual decay. That shape is called the envelope and the part of the synth that creates it is the envelope generator.

Filter: An electronic sieve — the size of the holes and their efficiency can be controlled. An electronic music filter is used to modify the bright oscillator waveforms by only letting through a certain band of frequencies.

LFO: Low Frequency Oscillator. Usually the main modulation source on smaller synthesisers. Square wave for trills, sine or triangular for vibrato or PWM. There is always a conflict between needing a fast vibrato and a slow chorus sweep rate.

Oscillator: The primary sound source of the synthesiser. It is a circuit which switches on and off rapidly repetitively, so producing the electrical signal we hear as a sound.

Ring modulator: This is the circuit behind the Dalek voice and scrambled telephones. It gets its name from the ring of four diodes once used between a pair of transformers to build the device before the days of integrated circuits. The modulator has two inputs, the signal and the carrier. The output is the sum and difference between these frequencies and their harmonics. Sine waves can be used to obtain bell tones, but waveforms richer in overtones produce a distorted mess.

Sample and hold: A circuit which is fed a continuously changing voltage. When it's triggered, say by pressing a key, it will instantly "sample" its input, and hold the exact voltage being fed to it at that split second. The most popular use is to feed it with white noise where every frequency is present, but shifting around very fast, so the sample will pick out a different, random frequency every time and the speed of its selection is usually governed by an LFO.

Sequencer: A circuit which will repeat a series of voltages at a speed determined by a clock oscillator. The voltages are commonly used to drive VCOs and so play a melody. There are many types which differ mainly in programming techniques — some use potentiometer controls, while others learn from the keyboard in real time.

Vocoder: A complex device which analyses the "excitation" input, usually your voice, then superimposes its characteristics over the top of a synthesiser sound. Classic examples are "Sparky's Magic Piano" and "Mr Blue Sky".

White noise: Though it's predominantly used for wooshy surf and wind sounds, white noise actually contains a random mixture of all the frequencies the synth can produce. Pink noise is white noise with an extra bass boost.

CONTROLS



ADSR: Attack, decay, sustain, release. See under individual headings.

Attack: The period of a sound envelope during which the volume builds to its loudest. This may happen rapidly as with a piano or slowly as with a pipe organ.

Decay: Once a sound envelope has built to its maximum volume it will then fall away to a lower level, and that's known as the decay — very short for percussive organ sounds with a click at the beginning, slightly longer for plucked piano sounds.

Sustain: The odd one out in ADSR — all the others are times, sustain is a voltage. It is the level in a sound envelope to which the decay falls determining how loud the sound is while the key is still being held down.

Release: The period of a sound envelope during which the volume falls to nothing once the key has been released.

Brilliance: Treble boost.

Bypass: To sidestep a sound treatment and continue to the next. It is common for the VCA to be bypassed to allow a sound though without a key being held down.

...filter


Bandpass: Not a ticket to get you into the beer tent, but a characteristic of a filter. The term refers to an upper and lower frequency limit outside which a signal is considerably reduced in volume.

Cut-off: The control which determines the frequency at which the filter takes effect.

Hi-pass: A filter characteristic which lets through high frequencies and cuts down bass ones. A HiFi rumble filter is high-pass.

Low-pass: A filter characteristic which lets through low frequencies and cuts down treble ones. A HiFi scratch filter is low-pass.

Notch: A filter characteristic which removes only one frequency — i.e., a hum filter. Several notch filters cascaded form a comb filter which are better known as phasers and flangers.

Q: A term meaning the quality of a filter. Essentially the same as resonance.

Resonance: Blowing over the top of a bottle gives a note — at the resonant frequency of the bottle. There is one frequency at which the bottle will sing and no other. In a similar way an electronic music filter can be peaked to ring at just one frequency. The resonance control dictates how selective the filter is.

Roll off: Yet another filter characteristic which describes how steeply frequencies outside the centre or corner frequency are cut back. Most electronic music filters are 24dB/octave which means that for a low-pass filter, a signal one octave higher will be about 16 times smaller than a signal at the cut-off frequency.

KEYBOARDS



Frequency: A measure of how high or low a tone actually is and which can be verified in a laboratory with instruments. Pitch, on the other hand, is how low or high our brain tells us a tone is.

Hold: The facility for the synthesiser to remember the last note or chord played on the keyboard when the hand is taken away.

Keyboard tracking: A keyboard works by feeding the synth a set of voltages. The higher the note, the higher the voltage and any function on the synth can be made to follow or "track" these changes. For example, a filter can be made to produce a brighter sound for high notes than it would for low ones. The release time on an ADSR envelope can produce longer fades for low notes than the high notes, good for piano sounds where the bottom strings will always take longer to die away.

Portamento: The effect a synth has of sliding from the last note you played to the new one you're holding down instead of jumping instantly between them. Also known as glide. Glissando is a similar effect but the synth will then pick out and play every individual note between the two that you've selected.

Pulse width: Oscillators are like blinking lights, on/off, on/off, but operating so fast that they blur into a sound of a particular pitch. For a square wave the length of time it's on, compared to the length of time it's silent, is interpreted as the mark to space ratio.

If their times are equal the ratio is 1:1 and the sound is rich and flutey. The width of the pulse, i.e. the on half, is the same as the width of the silence. On many synths this is often shown on the control as 50 per cent. If the silence becomes longer, taking up 90 per cent of the time, then the pulse width shrinks and the sound becomes more shrill.

Repeat: The facility to trigger the envelope generator repeatedly from the LFO during the period of a key press. If you're into synthesising banjos and mandolins then this one's for you.

Reset: A control which will chop a long release time to zero. Useful for sudden endings.

Ribbon controller: A strip of conductive material which operates like a normal rotary control on the front panel that has been "unrolled". Instead of turning the control to a certain point, you place your finger in the right position on the strip. Often used to vary pitch for slides between notes.

Sync: Synchronisation is a way of locking two oscillators so one will always be at a fixed multiple of the frequency of the other. Sweeping the oscillator in sync will cause it to "saw" up and down the harmonic series of the other producing a "screaming" effect.

Touch: Some keyboard controllers produce a dynamic voltage proportional to how hard or fast a key is pressed. This may be used to control volume or brilliance, etc. Second touch is the facility to trip a microswitch by pushing harder on a keyboard which is hinged and sprung. This additional trigger can be used to generate note bends and growls.

Transpose: To shift the starting pitch to another. Up or down two octaves is common, but some synthesisers such as the Lyricon have tonic, fifth, minor sixth, etc, settings to mimic those instruments such as saxophones whose written notes are not those actually produced.

...waveforms


Waveform: If you studied an oscillator on an oscilloscope it would have a distinct profile determined by the number of harmonics it had. Harmonics are like copies of the basic, "fundamental" note, but at multiples of the original frequency. For example, the second harmonic is exactly an octave up and many different harmonics can be mixed together. An oscillator's profile or "waveform" will depend on how many it can contain, and which ones.

Sawtooth: A signal waveform containing odd and even harmonics which is characterised by its rapid return to zero level after building to a maximum.

Sine: A signal waveform containing no harmonics. It is a pure tone which is dull to listen to, but good for modulation.

Square: A signal waveform containing only odd harmonics. It is a rectangular wave with a 1:1 mark/space ratio.

Triangle: A signal waveform that contains only a few harmonics so it is often substituted for a sine wave as it is easier to produce, electronically.

BUZZWORDS



Analogue/digital: The easiest analogy of this befuddling subject would be between an oil painting and a newspaper photograph. The oil painting is made from solid layers of pigment that gradually blend into each other — it's a continuous "analogue" process.

The newspaper photograph may look the same, but if studied closely is actually made from thousands of tiny dots. The shade depends not on the colour of the dots — they're all black—but on how many there are and how closely together they are packed. When the eye is far enough away it can't distinguish the dots, but visualises the picture as a whole.

Similarly it's possible to represent sound in the form of millions of digital "dots" rather than a continuous process. True digital synthesisers which are quite new shouldn't be confused with digitally programmed synthesisers which have been around for a couple of years.

In the latter it's the information about control settings, pitch, keys being played etc, that are represented as digital events because integrated circuits find it easier to remember many thousands of on/offs — the black dots and the white newspaper background — rather than the continuous shading of the oil painting.

Computer Synthesis: (see analogue/digital above). If the digital synth is the newspaper picture, then the computer synth is the entire newspaper and Sunday supplement. Its massive memory space enables it to carry out many sophisticated operations on the digital information.

Remember, computers don't get more clever, they simply get bigger and are able to do more and more simple jobs until eventually the task appears very complicated — such as the exact reproduction of all the tiny nuances within the sound of one note on a grand piano.

Linear/log: A simple mathematical law where each step up the ladder is one unit higher than the last. In a logarithmic scale, each step is double that of the last. Synthesisers use log oscillators because they are easier to control across the keyboard. In a one volt per octave system, if five volts equals a particular note, then the next step up will be six volts and the pitch will have doubled and be exactly an octave higher.

Modular synthesiser: An instrument where all the filters, oscillators, envelope generators etc are contained in separate boxes and can be patched together in whatever order you want.

Patchcord: A lead to connect the various inputs and outputs of a modular synthesiser.

Prepatched: A type of synthesiser — such as the classic Minimoog — in which the sound sources are connected to the sound treatments in a fixed order and no alteration is possible.

Preset: A type of synthesiser where few controls are provided, but instead voices are selected by a bank of buttons usually bearing the names of conventional instruments.

Programmable: The facility to record and recall sound settings.

Z-80: The name of the microprocessor brain inside synthesisers such as the Oberheim OB-X and the Moog Source.

CV — Control Voltage: Each note on the keyboard has an identifying voltage and this can be sent to another synth from an output on the rear panel to tell it what pitch to play. The second synth also needs instructions on when to start this note and when to stop — a trigger.

That's carried by the GATE output which provides a signalling voltage for as long as the key is held down. Different synths have different systems so not all of them can be patched together. Many work on the idea of a one volt increase in the control voltage for every octave increase in pitch. Some will provide a positive gate voltage, others a negative one.

Though manufacturers are gradually coming in line with each other, there's a long way to go yet and the advent of digital synthesisers will only serve to confuse the system even more. Now all the LATEST Rolands, Moogs, Korgs and Prophets include a one volt per octave CV and a positive gate.

Octave: A group of eight notes which form the diatonic scale. An octave above means a note double the frequency. Sometimes octaves are referred to by the length of the organ pipe required to produce them. Hence 16 foot pitch is one octave lower than 8 foot.

Multiple trigger: The facility to generate a new trigger signal without releasing the previously held key. This cleans up lazy fingering but does remove some control from the player. It is a must for short punchy envelopes.

MODULATION



Modulation: Effects such as vibrato, wah wah and tremolo which are introduced to an already established sound as part of the live performance, normally brought about by an LFO.

Chorus: A circuit which introduces a changing time delay into a signal so that when it is mixed with the original it gives the effect of multiple voices.

Delay: (a) Delay vibrato is a fading in of the modulation signal to simulate the technique much loved of violinists, (b) Trigger delay starts a second envelope shortly after the first to synthesise doubly strung instruments such as 12 string guitars and harpsichords.

Pulse width modulation: An LFO that slowly changes the pulse width of a square wave from fat to thin to back again introduces a chorus-like effect, as if there were two oscillators slightly out of tune, rather than one.

Wheel mod: A control to introduce an amount of modulation signal proportional to how far the wheel is turned from rest. It can be used during performance to bring in vibrato to a sustained note in the manner of a violinist.

X-Y controller: To you — a joystick. These are used to give one handed control over two functions such as LFO speed and modulation depth. Accurate control of pitch is impossible.

X-Mod: The facility for the output of one oscillator to feed a voltage control input of another and so cross modulate. This can give very rich output waveforms in the absence of a ring modulator.



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Synth Computers

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Angle Of The Dangle


One Two Testing - Copyright: IPC Magazines Ltd, Northern & Shell Ltd.

 

One Two Testing - Nov 1982

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Synth Special

Feature by Andy Honeybone

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> Synth Computers

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