|
Computer Music: Musc 216
JSYD Tutorial 8
LFO Modulation
of Frequency
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 frequency.
Using the patch you created in the 1st tutorial (Creating
a Simple SYD Patch), the following tutorial will show you how to
use an LFO (low frequency oscillator) to modulate the
frequency of the original sine wave operator. Systematic
modulation of the frequency by a rate less than about 20 Hz (the
optimum rate is 7 Hz) is also referred to as VIBRATO.
Vibrato is the effect which is created when a string play "wiggles"
the left hand on the finger board. It is also the effect that is characteristic
of opera singers in the European tradition.
Do this:
Open the LFO Modulation of the Amplitude
patch you created in the last tutorial. It should look like
this (except it won't have the comment and arrows):
Move the cursor over the link you have made between the two oscillators
until the cursor changes to a PEN (instead of a finger pointing).
Hold down the CONTROL KEY and click on the connection until you
get a pop-up menu.
Select the "Frequency Modulation (fm)" option:
Note how the BLUE connection line changes to a GREEN connection line.
This color coding is designed to alert you to the different types
of connections, AM (amplitude modulation=blue)
and FM (frequency modulation=green).
Select the original sine wave operator (the one on the right) and
change the frequency field so that it contains the value, 440+fm (see
below):
Also, change the value in the Amplitude field to .5 (be sure it's
5 TENTHS and not 5).
Now select the LFO modulation oscillator operator (the one on the
left) and change the various parameter fields so they contain these
values:
Note the value of 10 (!) in the amplitude field. Don't worry,
this is the correct value. This value of 10 is not the output
amplitude but is the amount of modulation which will be added to the
frequency in the original Oscillator operator. Later, you can
experiment with changing this value to various amounts in order to
discover how that will affect the sound.
Click OK and close this window.
Click the "Synthesize" button located in the bottom top 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.
When you are ready to proceed, click the "Play" button located in
the top left corner of the patch window. You should hear the
sine wave play in your headphones and hear a definite modulation of
the frequency corresponding to the 2 Hz frequency of the modulation
oscillator. The depth (amount) of the modulation will be represented
by the wide variation of the frequency. Or, click the link below
to hear sound:
JSYDSound6.aiff
Main Page
Back to the JSYD Tutorials
Index
|