Sampling Rate and Bit Rate Flashcards
What was once a consequence for too low a sampling frequency in films?
In an old film, wheels may appear to travel backwards as the time interval between images is too long and in this time the wheels may make a full rotation. The sampling rate/sampling frequency is too low.
What’s sampling frequency?
Sampling frequency is the full number of samples taken each second.
How can a varying signal be accurately sampled?
For a varying signal to be accurately sampled time between samples must be shorter than the time in which important changes occur. Too large a time interval will lose detail.
What two conditions must be met to sample with accuracy?
The signal can’t contain frequencies above a certain maximum.
Minimum sampling rate must be greater than two times the highest frequency component.
What happens if the signal contains frequencies above the maximum component? How does this happen in humans?
If the signal contains frequencies above the maximum component, the signal won’t be reconstructed accurately. Lower frequency signals, aliases, which aren’t present in the original signal will be generated.
In human hearing, samples with frequencies above 20kHz must have these frequencies filtered out to prevent creation of spurious low frequencies, aliases. In music, sampling must be greater than 40Hz.
What’s bit rate?
Bit rate is the transmission of information's rate. Bit rate ( bits s^-1 or Hz) = samples per second x bits per sample.
How must the sample rate be for composite waves?
For a composite wave which isn’t sine, sampling frequency must be at least twice the highest component of frequency.
How does aliasing affect sound and image quality?
Aliasing can also happen in digital pictures which makes them blurry, and reduces sound quality.
How does bit rate work in stereo channels?
For two stereo channels (left and right), the bits from both samples will combine and the bit rate is doubled.
What are disadvantages of digital signals?
People hear about tragic events as they happen creating a sense of responsibility and guilt.
Digital signals are numbers which can be edited and this makes banking details vulnerable. A rise in cyber terrorism could occur.
Images can be photoshopped to give a false sense of perfection.
What’s the formula for signal duration?
Duration (s) = no of bits in a sample / bit rate (Hz)
