Higher Computing Science Representing Sound

2. Synthesised Sound
• Synthesised sound is generated by a sound card.
• MIDI (Musical Instrument Digital Interface) is an example of
synthesised sound.
• Details of the pitch, duration, tempo, amplitude and volume are stored.

3. Digitised Sound
Analog sounds are captured and converted to a digital signal by the sound
card.
This is known as sampling.

4. Sample Rate
 Sample Rate is a measure of the number of samples per second
 Measured in Kilohertz (KHz)
 1 KHz = 1000 samples / second
 CD standard = 44.1 KHz

5. Sample Rate
A low sample rate will result in inaccurate audio output – the sample will sound
choppy.

6. Sample Depth
 The number of bits used to store each sample (also known as bit depth)
 An 8 bit sample depth is restricted to 256 unique audio values
 CD standard = 16 bit sample depth = 65,536 unique audio values
 DVD standard = 24 bit sample depth = 16,777,216 unique audio values

7. Sample Quality
 Increasing the sample rate increases the quality of the audio output
 Increasing the sample depth increases the quality of the audio output