## Material Summary

In this lecture we deal on Continuous signals, Linearity, and of course, some MATLAB.

## Continuous Signal

Continuous signal is a signal that varies with time, and can be represented as a function of time, x(t).

Examples : Sin waves, Sound, AC/ DC currents

Take sound as an example, with absence of sound, the air pressure, x(t) is a constant value, approximately $10^5 N/m^2$.

A plot of air pressure with respect to time with no sound energy

Thus, if there's sound, there would be varioation of air pressure about the atmospheric pressure.

A plot of air pressure with respect to time with a low-frequency sine wave. This sound would probably not be audible, but is presented with such a low frequency in order to actually see the waveform.

As the pressure varies around x(t) = $10^5$, we gauge shift the graphs such that it is pulled down to 0.

A plot of air pressure with respect to time with a low-frequency sine wave. The "resting pressure" of air has been removed, so that the sine wave oscillates about the time axis.

Using any examples, one can notice that while the sound's amplitude increases, the louder the voice is. In the other hand, if the frequency increases, the higher the pitch is.

This is quite noticable if you had a sound editing program. Observe the frequency change when the pitch changes, and the amplitude change when the loudness changes.

## Matlab

A very simple example of matlab code to produce the note "A" :

delta = 0.00005;
t = 0:delta:5 ;
y = sin(2*pi*440*t);
sound (y, 1/delta);