Q.When reading about synthesizers, I often see the term "filter." What does it mean?


What is the "filter" in a synthesizer?

Different instruments have their own unique sound characteristics, and therefore they sound quite different from each other even when played at the same pitch. For example, a "G" note played by a trumpet will sound quite different from a "G" note played by an oboe. This is because the sound of each instrument contains frequencies (overtones) in addition to the "fundamental" frequency that determines the pitch we perceive. These overtone differences are what the human ear perceives as differences in sound, allowing us to identify a particular instrument.

Now, let's look at the process of how a synthesizer's sound generator creates various sounds. To begin, the "oscillator" section generates the waveform that is the basis of the sound. You can select a square wave, sine wave, or sampled waveform (a piece of sound digitally recorded from an acoustic instrument, etc.), thus determining the basic character of the sound (the overtone structure).

However, to create the diverse range of sounds we expect from a synthesizer, we need to further process this waveform. This is where the synthesizer's filter section comes in.

To process the waveform, the filter section is used to add or remove specific frequency regions in the sound. The way in which these frequency regions are added or removed can be varied over time to create a variety of sound changes. Filter settings modify the tonal character, changing the sound to make it brighter, crisper, duller, thicker, or warmer.

After being processed by the filter section, the sound is then further modified with the amplifier section. The amplifier allows you to alter the sound's volume characteristics with attack, sustain, decay, and release controls.

Using all of these processes, we can create "synthesizer-like" sounds.
Note:Terms used in Roland products

On most of Roland products, the oscillator, filter, and amplifier sections of the sound generator are named with the following terms.
SectionTerm used on Roland products, and its meaning
OscillatorWG(Wave Generator)
Oscillator that generates a waveform
FilterTVF(Time Variant Filter)
Filter that varies its values (parameters) over time
AmpTVA(Time Variant Amplifier)
Amplifier that varies its values (parameters) over time


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