The Types of Oscillator

- Oct 17, 2018-

The oscillator, the most primitive source of sound produced by the synthesizer, produces a variety of sounds. They come in a variety of shapes and can be made from a variety of different techniques to give you the sound you want. If you think that all the sounds are turbulent in the air, then the oscillator is the device that produces the synthetic shock and is finally sent through the speaker. Unlike the up and down vibration of the guitar strings, the oscillation of the oscillator is generated based on the positive and negative periods of the voltage.

If the period of this oscillation is in the range of 20-20000 times/second, then the sound produced is the sound that the human ear can hear. The frequency of this oscillation determines the frequency response and the pitch of the sound, and finally they are adjusted to match the key to produce the pitch. We refer to a complete oscillation as a cycle and then name it different waveforms based on their shape. The shape of the waveform produced by the oscillator directly determines the tone and brightness of the sound.

Sine, Triangle, Sawtooth, and Pulse or Square, are the four most widely used synthesizer base waveforms. A sine wave is the purest waveform that represents each individual frequency, also known as a fundamental. Other waveforms add harmonics or overtones to the sine wave. This increases the brightness, complexity, and other characteristics of the sound. The sawtooth wave is the most harmonic waveform, because all integer multiples have harmonics based on the fundamental frequency. In other words, when you play a 100Hz sawtooth wave, harmonics of 200Hz, 300Hz, 400Hz, etc. are generated at the same time. The amplitude of each successive harmonic is decremented, and you can also understand the decrement of the volume until the amplitude is decremented to half of the fundamental. This continuous decrement produces a decreasing sawtooth waveform.

Both triangular and square waves have odd harmonics, but their amplitude fading rates are not the same. In a triangular wave, the continuous harmonic amplitude decreases by 1/3, while the sawtooth wave decreases by 1/10. When you play a square wave and a triangle wave, they all produce an odd multiple of 300Hz, 500Hz, 700Hz, etc., but the waveforms are different because of their different amplitudes.

Square waves are also known as pulse waves because they are replaced back and forth between positive and negative values. Pulse width refers to the balance between the positive and negative sides of the waveform. Changing the pulse width changes the harmonic content of the waveform, producing a phase effect, which is Pulse Width Modulation (PWM).

Synthesizers also typically provide a source of noise, including white noise, pink noise, and other noise. Noise usually refers to a large number of randomly generated frequencies, and color refers to the amplitude relationship between these frequencies. White noise distributes the average energy over a linear frequency, while pink noise distributes the average energy over a logarithmic frequency. This means that pink noise is related to the frequency and amplitude of the human ear. But from the auditory point of view, white noise is brighter than pink noise, because white noise has more energy at high frequencies.

Low frequency oscillators, or LFOs, are also common synthesizer components. They can use oscillator waveforms that are used as sound sources, and sometimes make people hear sounds, but more importantly, they can produce frequencies much lower than the human ear's hearing range. This slow cycle waveform can be used as a modulation source to control different synthesizer parameters. For example, with a triangular wave LFO to modulate the pulse width, you can get a flanger effect to make a pad-like sound. In LFO, noise is often used to obtain random parameters, similar to Sample & Hold. In this case, random parameters are acquired at a specific frequency, or acquired according to tempo, and then held to the next sampling point. This allows you to get random step parameters or add uncertainty to the sound as needed.



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