Section 3 - Data representation Flashcards
what is the sample rate
the sample rate is the frequency with which you record the amplitude of sound
what is the equation to calculate sample size
samples per second * bits per sample * length of sample per second
what happens during analog to digital conversion
- the analogue to digital converter (ADC) samples the analogue data by measuring the wave at each point
- then it gets converted into a binary value
what is Nyquist’s theorem
in order to produce an accurate recording, the sampling rate must be at least double the highest frequency
what is frequency
the frequency of a sound is the speed of vibration of the wave (pitch)
why is a MIDI file better than a live recording
- uses less disc space
- music is easily manipulated e.g. music can be played by another instrument or in another key
what is compression
reduce the storage space of files
what is lossy compression
removes non essential information, means some quality is lost
what is lossless compression
records patterns in the data rather than actual data
results in larger files than lossy, but no quality is lost
what is run length encoding (RLE)
rather than recording every pixel in an image, it records its value and the number of times it appears
what is dictionary based compression techniques
compression algorithm searches through the text to find common words to enter in a dictionary and translates the message
what is encryption
the transformation of data from one form to another to prevent an unauthorised third party from being able to understand it
what are plaintext and ciphertext
plaintext is the original message, and ciphertext is the encrypted data
what is the Caesar cipher
a cypher that shifts the letters of the alphabet along a given number of keys
what is the Vernam cipher
