12 juin 2014 ~ 0 Commentaires

Coursera : Week6 – Explain the usage of the 5 most important synthesis modules

Oscillator

On a synthesizer, oscillators are the sound generators.
They generate sound based on a waveform.

They can generate sound from basic waveform like we saw previously in the course :

Sin, square, triangle, sawtooth :

Each waveform has a different sound property :

Sine : it’s energy at a single frequency
Square : produce only odd harmonics
Triangle : produce also only odd harmonics but they roll off faster than square wave in the high frequencies
Sawtooth : produce odd and even harmonics. This waves generate the brigtest sound

In this synthesizer, more waveforms are available with differents properties :

In a synthesizer you can have severals oscillators and cumulate their signals. The addition of two waveform produce another sound, this is called additive synthesizis.

Filter

After being generated by one or more oscillator, the sound is going through a filter :

You often or maybe always filter an oscillator sound in order to sculpt it.

The most used filter is a lowpass because the high frequencies are very often agressives.

This is substractive synthesis.

Common types of filters are :

Low pass :

High pass:

Band pass:

Notche:

In some synthesizers, there will be other filter types :

You may have in your synthesizer one or more filters, and they may work in serial or parallel:



This allow you to :

  • Filter one oscillator’s sound twuce or more.
  • Filter each oscillator sound with a different filter type.






  • Amplifier :




    The amp section allow you to control the volume of the synthesiser.
    it’s a very common modulated property of a sound.



    Envelope :

    This is one of the modulation source of a synthesizer.

    This is a path that a modulated component of the synth will follow if applied.

    The envelope is player-dependent, it only apply when a midi note is played.

    From Wikipedia :

    «
    • Attack time is the time taken for initial run-up of level from nil to peak, beginning when the key is first pressed.
    • Decay time is the time taken for the subsequent run down from the attack level to the designated sustain level.
    • Sustain level is the level during the main sequence of the sound’s duration, until the key is released.
    • Release time is the time taken for the level to decay from the sustain level to zero after the key is released.
    »

    I would like to point out that for the release time definition, I think it’s not always from sustain level that the level will decay.

    Like we saw in the video courses, the release start to decay when the key is released, but it decay from the current level at this given moment.

    If when the key is released, the level was at the end of the attack, the level may be different from the sustain level, at the start of the release phase.

    Eg : if we apply this envelope (modulation source) to the amplifier (modulation destination), the volume will follow the path :

    A short attack : The volume raise quickly but with a little progression, allowing us to eliminate clicks at the start of a sound.

    The sound goes from 0 to 100% volume level in order to create a earable transient.

    A long decay : the sound diminuate progressively to 50% of volume (Sustain).

    Release : a pretty short release, when the note is release the volume goes back to 0%. A little progression on the release too allow us to eliminate clicks when the key is released.

    LFO

    An LFO is a low frequency oscillator, like the envelope, it’s another modualtion source of a synthesizer.
    Here are the most importants properties :

  • Curve : Modulation path (common sine, square, triangle, and many others )
  • LFO ratio : Modulation speed (how fast the modulation path is followed, synced or not to the BPM)
  • This modulation is not player dependent as it can run even if a note is not played.

    Common type of use is :

  • On an oscillator pitch, a very little modulation can make a little vibrato
  • On a lowpass filter, associated to the frequency it can be used to make wobbles.
  • Many others …



  • Reviewing the basics of synthesyzers allow me to better understand me and improve my skills in sound design ! That was a great course !