2.6 Sound Flashcards
analogue recordings
- caused by vibrations travelling through a medium
- changes in the air pressure are converted into voltage changes
sound sampling
samples/snapshots of sound are taken at regular intervals
sampling frequency
how often samples of the sound wave are taken
a high sampling frequency gives a more accurate reproduction of the analogie waveform
sampling frequency for CDs and Blu-ray
CDs: 44.1 kHz per second
they are recorded in stereo and so the file size will be doubled
blu-ray: 9.6 kHz per second
digital sound recording
transistors are either on or off, and cannot continuously reproduce sound
digital recordings use snapshots of the sound at regular fixed intervals and them play them back one after the other
these are called samples
bit depth
- describes the number of bits used to encode each sample
- a high bit depth allows more data to be stored and allows the dynamic (volume) range of the sound to be more accurately represented
- using 8 bits allows 256 graduations of volume
- 16 bits allows 60000
- 24 bits allows 16.7 million
dynamic range
range of volume in the sound
What does the quality of the digital audio depend on?
sample frequency
bit depth
bit rate
amount of data processed every second
bit rate = sample frequency x bit depth
file size = bit rate x recording length (s)
Calculate the file size in MB of a digital audio file of 3 minutes duration with a sampling frequency of 44.1 kHz and a bit depth of 16 bits
You may use the decimal prefix 1000 in your calculation [2]
15.87 MB
When digitising sound, state what is meant by:
a) sampling frequency
b) bit rate [2]
a) number of sound samples that are taken each second
b) amount of data processed every second
Calculate the file size in megabytes of a stereo audio file if the duration is 2 minutes 30 seconds and the sampling frequency is 44.1 kHz with a bit depth of 16.
You may use the decial prefix 1000 in your calculation. [2]
26.5 MB
