Sampling

Sampling

1. Signals

   • Digital signals have fixed values
   • Analogue signals vary constantly

2. Digital signals are resistant to the effects of noise

   • When signals are transmitted they pick up noise
   • It's easier to reconstruct a digital signal because they have a limited number of values

3. Digitising analogue signals

   • Turns it into a digital signal
   • Take the analogue value at regular time intervals, then find the nearest digital value
   • Analogue value is converted to binary numbers
   • Digital value is not always the same, but very close

4. Quality and Resolution

   • How well the digitised signal matches the analogue depends on 2 factors
     • The difference between possible digital values (resolution)
     • Time from one sample to another (sampling rate)
   • The higher the resolution, the closer the match
     • The same applies for the sampling rate
   • Resolution is the number of bits in the binary numbers representing the digital values
     • More bits = higher resolution
   • CDs have a 16 bit resolution

5. Noise

   • Limits the number of bits used for sampling
   • Resolution is limited by the ratio of total variation in the signal to the variation caused by noise

6. Advantages of Digital

   • Sent, received and reproduced easier than analogue
   • Resistant to the effect of noise
   • Easy to process using computers
   • Represent different kinds of information in the same way

7. Sampling Rate

   • High enough to record all the high frequency detail
   • Low sampling rate can create low frequency signals (aliases) which weren't in the original signal
   • Minimum sampling rate = 2 x maximum frequency