types of signal

Analog Signals

The pictures we saw above are examples of analog signals:
An analog signal varies some physical property, such as voltage, in proportion to the information that we are trying to transmit.
Examples of analog technology:
1. photocopiers
2. old land-line telephones
3. audio tapes
4. old televisions (intensity and color information per scan line)
5. VCRs (same as TV)
Analog technology always suffers from degradation when copied.
When sound is transmitted or stored it may need to change form, hopefully without being destroyed.

Sound moves fast: in air, at 340 m/sec = 750 miles per hour. Its two important characteristics areFrequency (aka pitch) and Amplitude (aka loudness).

Digital Signals

With a digital signal, we are using an analog signal to transmit numbers, which we convert into bitsand then transmit the bits.
A digital signal uses some physical property, such as voltage, to transmit a single bit of information.
Suppose we want to transmit the number 6. In binary, that number is 110. We first decide that, say, "high" means a 1 and "low" means a 0. Thus, 6 might look like:

The heavy black line is the signal, which rises to the maximum to indicate a 1 and falls to the minimum to indicate a 0.