Digital Sound & Music: Concepts, Applications, & Science, Chapter 2, last updated 6/25/2013
30
fplot('2*sin(262*2*pi*t)', [0, 0.05, -2.5, 2.5]);
After multiplying by A=2 in the statement above, the top of the sine wave goes to 2 rather than 1.
To change the phase of the sine wave, we add a
value

. Phase is essentially a
relationship between two sine waves with the same frequency. When we add


to the sine
wave, we are creating a sine wave with a phase offset of
-2.5,

compared to a sine wave with phase
offset of 0. We can show this by graphing both sine waves on the same graph. To do so, we
graph the first function with the command
fplot('2*sin(262*2*pi*t)', [0, 0.05, 2.5]);
We then type
hold on
This will cause all future graphs to be drawn on the currently open figure. Thus, if we type
fplot('2*sin(262*2*pi*t+pi)', [0, 0.05, -2.5, 2.5]);
we have two phase-offset graphs on the same plot. In Figure 2.31, the 0-phase-offset sine wave
is in red and the
180o
phase offset sine wave is in blue.
Figure 2.31 Two sine waves, one offset
180o
from the other
Notice that the offset is given in units of radians rather than degrees,
180o
being equal to π
radians.
To change the frequency, we change . For example, changing to 440*2*pi gives us a
graph of the note A above middle C on a keyboard.
fplot('sin(440*2*pi*t)', [0, 0.05, -1.5, 1.5]);
The above command gives this graph:
0 0.005 0.01 0.015 0.02 0.025 0.03 0.035 0.04 0.045 0.05
-2
-1
0
1
2
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