Computer Music: Musc 216
SYD Tutorial 7
(Version 108b2.1)

LFO Modulation of Amplitude

LFO is an abbreviation for "low frequency oscillator."  Modulation refers to the way one signal is changed systematically by another signal.  Consequently, LFO modulation refers to the process by which an oscillator using a low frequency (usually below the threshold of human hearing, 1 - 20 Hz) can systematically change the state of another oscillator, for example, its amplitude.

Using the simple patch you created in the 1st tutorial (Creating a Simple SYD Patch), the following tutorial will show you how to add another operator which will modulate the output amplitude.  Systematic modulation of the amplitude is also referred to as, TREMOLO.

Do this:

Open the patch you created in Tutorial 4 .

Add a second oscillator operator and connect it to the first operator so that it looks like this:

Double click on the ORIGINAL SINE WAVE OPERATOR icon (that's the one on the right) and change the amplitude filed so that it contains the variable, "am" :

    Note the variable, "am"
    in the Amplitude field.

Click OK and close the edit window.

Now double click on the new LFO MODULATION OPERATOR icon (that's the one on the left) and change the various parameter fields so they contain these values:

Note the value of "1"
in the frequency field.

Click OK and close the edit window.

Click the "Synthesize" button located in the bottom left corner of the patch window. You will not hear the sound of the patch until you "synthesize" it.

Make sure your headphones are connected to the audio output of the computer.  Also, it is assumed that you have already checked the system audio settings and your computer will produce audio output.  Be cautious and place your headphones in front of your ears until you become familiar with this level of the sound.

When you are ready to proceed, click the "Play" button located in the bottom left corner of the patch window.  You should hear the sine wave play in your headphones and hear a definite modulation of the amplitude corresponding to the 1 Hz frequency of the modulation oscillator.  Or, click the link below to hear sound.


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