ANALOGUE AND DIGITAL SIGNALS

    An analogue signal varies smoothly. It can have any value that you want. The signal from a microphone or loudspeaker is an analogue signal. Videotape and vinyl records are analogue recordings.

    A digital signal can only have certain fixed values. The particular digital signal shown above is binary: it can have values 0 and 1 (off and on), but nothing in between these two values – the Internet works with binary signals. Morse code is another form of digital signal (it can have three values – long, short or nothing). DVDs, CDs and most new toys are digital recordings.

Disadvantages of digital signals

  You have to convert the analogue signal into a digital form (analogue-to-digital conversion or ADC). You then have to convert it back to analogue to play it (DAC). This causes a few problems.

1. The ADC conversion can result in some loss of detail - an MP3 track is not quite a perfect reproduction of the original. To get better reproduction you need to store more digital information – CD tracks are better reproductions then MP3 tracks but require much more data to be stored.

2. The equipment needed to perform the ADC and DAC conversions causes additional complexity and cost in the recording and playback device. An analogue radio receiver is simpler and cheaper than a digital radio receiver.

Advantages of digital signals

  Increasingly, digital technology is the way forwards.

1. An important benefit of a digital signal is clarity. If the digital signal picks up any interference then it is still easy to see what the original signal must have been.

Digital signals can be transmitted without worrying too much about interference.

2. Modern digital devices can transmit digital signals very rapidly i.e. send huge numbers of ‘0’s and ‘1’s every second. This means that it doesn’t take very long to send or receive a huge data file (e.g. download an MP3 track).

3. Making a phone call doesn’t need many ‘0’s and ‘1’s each second; a fast digital device can send many more ‘0’s and ‘1’s than you are using for your call. You can use the spare capacity to send extra phone calls simultaneously down the same transmission line. Optical fibres and lasers are particularly good at this and you can send thousands of phone calls simultaneously down one optical fibre, greatly reducing the cost per call.