An amplifier receives a signal and increases its power. A power amplifier is primarily used to make a signal strong enough to “drive” a speaker so you can hear sound. For this reason, the power amplifier is usually the last section a signal passes through before it goes to the speaker to become a sound.
Attack refers to how quickly a sound reaches its maximum level (be it volume or brightness). For example, a thunderstorm and a surf sound are very much alike execpt for their attack characteristics. Thunder has fast attack as it starts with a loud bang. A surf sound has a slow attack as the waves approach slowly, getting louder and louder.
An Attenuator cuts down the level of a signal. For this reason it can control volume, balance or the amount of a control signal’s effect.
An inaudible signal that is used to control some aspect (pitch, volume, filter cutoff, etc.) of another audible signal. Read the “Modulation” definition.
Voltage, current and signal are often used interchangeably. We have chosen to use the term “Signal” in this glossary.
A typical sound consists of a fundamental tone plus a series of higher frequencies above it called overtones, or “harmonics”. A filter lets you “Attenuate” (reduce the volume of) the harmonics above (or below, depending on the filter) a given point of your choice. The frequency of that given point is called the “Cutoff Frequency”.
As its name applies, decay refers to how a sound ends. A fast decay means the sound ends abruptly, like a drum beat. A long decay means it ends gradually, like a cymbal.
The envelope of a sound is how quickly it builds (attack), sustains and fades away (decays). Every different instrument has a different envelope.
A typical sound contains a fundamental tone (the predominant note that you hear) plus a series of higher frequencies called overtones or “harmonics”. These harmonics contribute a great deal to the sound. The filter section of a synthesizer lets you control many characteristics of the harmonics - their highest level, attack, decay, etc. There are different types of filters. A low-pass filter allows only the frequency below its variable “cutoff frequency” to pass through it and eventually be heard as sound.
This control in the filter section lets you control the volume of the band of frequencies around the “cutoff frequency”.
Frequency is the number of cycles or vibrations per a unit of time, as in “cycles per second” -- cps. Sound, of course, is created by something vibrating -- a guitar string, a reed, the larynx in your throat. The frequency of that vibration determines the pitch of the sound -- the faster the vibration, the higher the note. Frequency is calibrated in Hz (Hertz). One Hz equals 1 cps. Concert pitch A is 440Hz.
A pitched sound (i.e. a note produced by an instrument) usually consists of numerous component sounds. The fundamental tone is the lowest frequency of these components and is the basic note that you hear. The higher pitches, called “harmonics”, are various frequencies that are whole number multiples of the fundamental frequency. Although you hear all these different frequencies, your ear still interprets the fundamental frequency as the musical note, while the harmonics serve to “color” the overall sound.
See “Oscillator” and “Modifier”
This control gives you “glissando” like a violinist creates sliding their finger up and down the neck. Glide slides the sound up (or down) from the previous note, and then slides it on to the next note played and so on. The speed of that “slide” is adjustable.
Harmonics, or “overtones”, are the higher frequencies contained in a typical pitched sound. The “fundamental tone” is the primary pitch you hear. It is usually accompanied by numerous higher overtones -- called “harmonics”. A violin is rich in harmonics. A flute, on the other hand, has very few, if any. The harmonic content of an instrument (which harmonics it produces and how they vary in strength as the sound progresses) largely determines its distinct sound. This is why a violin doesn’t sound like a trumpet, which doesn’t sound like a clarinet, etc. In a synthesizer, the waveform control lets you select different harmonic structures while the filter section lets you control the harmonics that are produced.
The mixer section in Dr. MOOG’s own words, “is a switchboard in the synthesizer”. It lets you select which of the the various sounds (or “signals”) in the synthesizer will be heard., and it lets you control the volume of each (or “mix” the overall sound). It then lets you route the signal to the next section of the synthesizer.
Modulation is a technique used for altering the signal that you’re routing through the synthesizer. This signal, of course, eventually becomes sound when it reaches the speaker, so by altering the signal you alter the sound. When you modulate this signal, you alter it by processing it with another inaudible “control signal”. To use Dr. Thomas Rhea’s analogy, the control signal acts like an “unseen hand” that jiggles one of the knobs on the control panel for you.
A guitarist, in a sense, modulates his sound when he jiggles the string back and forth (and thus, its pitch) to create vibrato. A trumpet player modulates the air column by jiggling the valve. A synthesizer modulates an electrical sound signal by jiggling it with the waveform of another signal. The signal doing the jiggling is called a control signal. The signal being jiggled is the modulated signal. Its also called the audio signal because it is the sound you actually hear.
There are several ways this control signal can modulate the sound signal (that is, there are several knobs the “unseen hand” can jiggle). You can modulate its amplitude so the volume alternates between loud and soft. You can modulate the frequency so that the pitch wavers up and down like a vibrato. If you modulate the filter cutoff, the harmonic content will sweep back and forth like a WAH-WAH pedal.
Your choice of control signals also influences the sound. The waveform of the control signal is what “jiggles” the sound signal, and different waveforms “jiggle” it differently. A sine wave (~) moves it back and forth smoothly and regularly. So, if the sine wave modulates the frequency, you will hear vibrato. A percussive waveform like this (^) alters the sound signal (its frequency, volume or whatever aspect of it you are modulating) quickly and then releases it gradually.
In other electronic media like hi-fi, radio, or walkie-talkies, noise is considered an undesirable interference. However, the MOOG Synthesizer puts noise to good use. Noise is the random distribution of all frequencies, like the static you hear rushing between TV stations. It has no pitch. Pink Noise is the same as White Noise, only with a lower bandwidth. The MOOG Synthesizer uses noise as a sound source that you can mold with other controls. It’s an excellent starting block to construct such sounds as steam locomotives, surfs, thunderstorms, wind and lots of special effects. Many musicians create sounds of non-pitched instruments with noise, like drums and cymbals. It can often add a nice soft “breath” to the musical notes you play.
An octave is the interval between two frequencies having a ratio of 2:1, in other words, the octave of a note is twice its frequency -- it is the same note, only a higher pitched version. Play any note on a piano and start counting each key (including the black ones) up the keyboard. You will hear twelve different notes, and the thirteenth will be the same as the note you started from, only an octave higher in pitch -- the octave. Moog’s keyboards can be raised or lowered several octaves at a time just by clicking the octave switch. This lets you tune your oscillators (which produce the initial musical sound) octaves apart, and it allows a small keyboard to have a wider octave range.
The oscillator is where the actual pitched sound of the synthesizer begins. All pitched sound is created by something vibrating -- a guitar string, a reed, your own larynx. An oscillator produces a tone (actually, a signal) by vibrating a voltage. That basic signal is later altered by you, using the keyboard and the different sections of the synthesizer. Then the signal is finally amplified enough to vibrate a speaker cone so you can hear it. But, it all starts with the oscillator.
If you consider that a synthesizer merely lets you route a signal through various sections, thus changing its character, then that route has to consist of inputs and outputs. The signal enters each section (or module) through the input, and exits through the output. This is why the MOOG’s modular systems with their patch cord connections are so versatile in constructing different signal paths and ultimately, different sounds.
A pitch bend device, like a ribbon controller or pitch bend wheel, lets you slide the pitch up and down manually, the way a guitarist “bends” a note by stretching a string or a trombonist moves the slide back and forth.
A preset tab lets you turn a whole set of functions (and thus, a complete sound or sound effect) on or off instantly, so you don’t have to tune each function in yourself with the various controls.
One of the easiest ways to understand what a sample and hold does is to consider the following analogy: “A camera samples (photographs) movement and holds a fixed image (the print). A sample and hold circuit photographs (samples) a moving voltage and prints (holds) a fixed voltage level.
Of course, the sample and hold operates continuously, taking one “photograph” after another to give you a rhythmical sequence of “printed” voltages. The speed of that rhythm is adjustable. Depending on how your sample and hold is utilized, you can create regular repeating patterns, or a completely random string of control voltages, which are then used to control the filters, loudness, contour, oscillators and other sections of the synthesizer (which, in turn, control the timbre, envelope, frequency, and so on).
You have heard the sample and hold in science fiction movies where they show the electronic laboratory or a computer scene. You have also heard it adding life to pop records, often playing “call and answer” to the band. Because of its steady rhythm, its especially exciting during otherwise typical drum solos.
We could call signal a lot of things, like “voltage” or “current” but we prefer to call it a signal. WE prefer to think of it as a flow of information that your route through the synthesizer and mold with the various controls until it finally exits the synthesizer and enters the speaker to become sound.
You don’t have to know what a voltage control amplifier, filter, or oscillator is to operate a synthesizer any more than you have to know what a cathode ray tube is to operate a television. It’s there, and all you do is turn the knob and it works. But, a lot of people are still fascinated by this concept that Dr. Moog developed and popularized.
Voltage Control is a very simple electrical concept that’s similar to some mechanical concepts. If you play a horn, you exercise mechanical sound control over a column of air. The air carries the sound, but you control the air with your breath, your lips in the mouthpiece, the valve that your fingers press, and so on. Likewise, if you have a voltage controlled oscillator producing a signal, you can control the frequency of that signal by applying different voltages to its control output. With a voltage controlled amplifier (which carries the strength of the signal) you can control the “gain” (or volume) by applying voltages. So, voltage control is an electrical way of controlling various aspects of sound, which before the age of electricity were controlled with fingers, tension bars, breath, bottlenecks and even the acoustical design of the instrument itself.
Pitched sounds are patterns of vibrations that repeat regularly at a rate anywhere between twenty and twenty thousand times a second (20Hz-20,000Hz). The waveform is a picture of the actual pattern in time -- of one complete cycle of a signal. For instance, in a waveform like this (^^), the air pressure of the sound wave slowly increases, and then instantaneously snaps back, once every cycle vibration. On the other hand, a waveform like this (HH) snaps back, stays there, then snaps forward, and stays there, once every cycle.
When slow electrical waveforms are used as control signals (to vary some aspect of the sound) you can actually “hear” the waveform by how it varies the sound. For instance, if you apply this waveform (^^) to the control input of a tone oscillator, you will hear the pitch go up, then go down once every cycle of the waveform. If this particular control waveform repeats every couple of seconds, the tone oscillator will produce a siren-like pitch change. If, on the other hand, the control waveform repeats five or six times per second, a vibrato will be imparted to the tone oscillator.
Harmonic content (spectrum) and waveform are two different ways of describing a sound. Harmonic content is a list of the different frequency components in a sound while the waveform is a picture of the sound pressure pattern in time. An engineer or mathematician can figure out what the harmonic content of any waveform is, but musicians don’t necessarily need this detailed knowledge. There are a few simple rules that will help you understand the relation between sound waveforms and the harmonic contents which they correspond. Here are those rules:
1. A smooth waveform generally has less harmonic content that a waveform with sharp corners.
2. Waveforms with sharp edges have high harmonic content, while waveforms with sharp, skinny peaks (spikes) have the highest harmonic content of all.
3. The more symmetrical an waveform is, the less harmonic content it has. Waveforms that are completely symmetrical (the bottom half is the mirror image of the top half) have only odd harmonics, and therefore have a hollow, woody, clarinet - like sound. Synthesizer oscillators generate very simple waveforms. Some popular synthesizer waveforms are : sine, triangle, square, pulse, saw
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