How is information passed through digital signals?
In digital signals, information is coded as binary and passed through wires, air, or optical fibres.
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Why are digital signals superior to analogue signals?
Analogue signals vary continuously. Sound is converted to PD. When signals weaken, noise is amplified. Filtering noise loses detail. Binary signals are on/off so it's easy to not lose information for digital signals.
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What is sampling?
Sampling - measure displacement of analogue signals regularly and convert to binary numbers. Coding at 3 bits gives eight quantisation levels.
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What is quantisation error and how is it reduced?
Quantisation error = difference between signal and quantisation level. More levels produces a better match
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What is resolution?
Resolution = PD range/no of levels.
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What is the effect of more quantisation levels?
Increasing the number of levels increases demand on data storage and transmission
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What is the maximum number of levels?
Max useful no of levels = V total/V noise = 2^b
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What is the sample rate? what happens when it's too low?
Wheels appear to move backwards when the sample rate is too low leading to almost a revolution every frame. Sample rate is no of samples per second. Sampling too slowly misses high frequency detail.
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What two things are needed to accurately reconstruct the signal?
Signal can't contain frequencies above a maximum, minimum sample rate must be greater than 2x highest frequency or else lower frequency signals, aliases, are made
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What sample rate is used for human hearing?
Humans can't hear above 20kHz so frequencies above this are removed before the signal is sampled to 40kHz or else aliases are made
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What is bit rate?
Bit rate = rate of transmission of digital information = samples per second * bits per sample
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What is duration?
Duration = no of bits in signal / bit rate
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What are consequences of digital signals?
Digital signals can be altered as numbers, making bank details insecure. Photos can be edited giving false sense of perfection.
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Other cards in this set
Card 2
Front
Why are digital signals superior to analogue signals?
Back
Analogue signals vary continuously. Sound is converted to PD. When signals weaken, noise is amplified. Filtering noise loses detail. Binary signals are on/off so it's easy to not lose information for digital signals.
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