The synthesizer

The working of a synthesizer: oscillators, filters, amplifiers, LFO

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  1. Hello, I'm Susi from Italy, and this post is for lesson 6 of Introduction to music production on Coursera.org.

    Today I'm going to talk about the usage of the most important modules within a synthesizer: oscillators, filter, amplifier, envelope, and LFO (low frequency oscillator).
    To illustrate how all of these modules work, I will be using Minimogue VA, a software emulation of the famous Minimoog synth.
  2. minimoog - SusiGi's library
    minimoog - SusiGi's library
  3. Oscillators

  4. Within a synthesizer, the oscillator is the sound generator. It creates sound based on a geometric wave form. Minimogue VA include three oscillators. All of them can be used to generate waveforms that can be combined together to emulate instruments or to create a completely new sound. The third oscillator also serves as an LFO.
    In the oscillator bank below, you can see the waveform knob of the first oscillator highlighted in yellow. There are several types of waveforms we can choose from: sinewave, two types of sawtooth wave, triangle wave, and three different square waves. Noise is only available on Oscillator 3.
  5. oscillators - SusiGi's library
    oscillators - SusiGi's library
  6. Filters

  7. After being generated by the oscillator, the sound reaches the filter bank.
    In the image below, you can see what the filter section of Minimogue VA looks like.
  8. filter - SusiGi's library
    filter - SusiGi's library
  9. This section include four knobs, the most important of which is the cutoff knob. The cutoff knob allows us to cut some frequencies and to let other frequencies pass into our sound. For example, we can use it as a low pass filter, which is the most important filter within a synthesizer, as it allows to remove higher frequencies and to get a smoother sound.
    Below the filter knobs, we also have a Filter Contour section. In this synth, contour is the word for envelope. In other words, the Filter Contour knobs allow us to modulate the filter envelope through ADSR controls.
    In the following short video, you can hear how the sound changes using different cutoff filter settings.
  10. Amplifier and envelope

  11. After passing through the filter, the sound reaches the amplifier, which is the module that controls amplitude over time.
    The amplifier envelope (called loudness contour in this synth) can be controlled through ADSR knobs.
  12. amplifiers - SusiGi's library
    amplifiers - SusiGi's library
  13. - A stands for Attack time: it is the time the sound needs to get from zero to full value when we press a key.
    - D stands for Decay time: it is the time it takes for a sound to fall from full value to sustain level.
    - S stands for Sustain level: it is the amplitude of the sound (after decay) during the time the key is pressed.
    - R stands for Release time: it is the time the sound needs to go from the sustain level down to zero.

    We can set the attack time, the delay time, the sustain level and the release time for each sound.
    In the video below, for instance, you can hear how attack time affects the sound. The first sound has a short attack time, in the second one the attack time is set to zero, whereas the last one has a very long attack time.
  14. LFO

  15. The acronym LFO stands for low frequency oscillator. The LFO is an oscillator itself, but we cannot directly hear it, as it runs under 20 Hertz, which is the lowest frequency audible by the human ear.
    In the picture below, you can see the LFO included in Minimogue VA.
  16. LFO - SusiGi's library
    LFO - SusiGi's library
  17. Even though the LFO is not audible, it is very useful to modulate the VCO (voltage controlled oscillator), especially to produce effects such as vibrato, wah wah or tremolo. If we cannot hear it by itself, we can distinctively hear its effect on the VCO. We can configure the oscillator level through a fader and the oscillator's destination using the right and left arrows. We can also choose between a sine wave or a square wave form. Let's see how a sound changes after configuring and applying the LFO to it.
  18. The impact of the LFO on sound is pretty amazing.
  19. Conclusion

  20. The synthesizer is a powerful tool to create and modulate all kinds of sounds. It takes a lot of time to fully learn how its modules work, though. It's a very interesting and fascinating journey. I've learned so many things in this last week, but I have a feeling that I will never completely master the subject. Perhaps that's what makes synthesis so enthralling.

    Thank you so much for reading my presentation and for your feedback, dear classmates! I can't wait to read and whatch your lessons!

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