9618 · 1.2.2
Multimedia - Sound flashcards
Revision flashcards for Cambridge 9618 Multimedia - Sound (syllabus 1.2.2). Flip, recall, then mark a real past-paper question.
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What is sampling in the context of sound?
The process of taking measurements of the amplitude of an analogue sound wave at regular time intervals. These measurements are then converted into digital values.
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What is Sampling Rate?
The number of samples taken per second. It is measured in Hertz (Hz) or Kilohertz (kHz). A higher sampling rate results in a more accurate representation of the sound wave, higher quality, and a larger file size.
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What is Sampling Resolution (or Bit Depth)?
The number of bits used to store the value of each sample's amplitude. A higher resolution allows for more distinct amplitude levels, resulting in better dynamic range, lower noise, and a larger file size.
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What is an Analogue-to-Digital Converter (ADC)?
An electronic device that converts a continuous analogue signal (like sound from a microphone) into a discrete digital signal through the process of sampling and quantisation.
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What is a Digital-to-Analogue Converter (DAC)?
An electronic device that converts a digital signal back into an analogue signal, which can then be output through speakers or headphones.
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What is quantisation?
The process of mapping the infinite possible values of a sample's amplitude to a finite set of discrete values, determined by the sampling resolution. It's essentially 'rounding' the measurement to the nearest available level.
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What is quantisation error?
The difference between the actual amplitude of the analogue sample and the value it is rounded to during quantisation. This can be perceived as a hissing or background noise, especially at low bit depths.
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State Nyquist's Theorem.
The sampling rate must be at least twice the highest frequency present in the original analogue signal to be able to accurately reconstruct it. For example, to capture a 20,000 Hz sound, you must sample at least 40,000 Hz.
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What is the formula for calculating the file size of an uncompressed audio file?
File Size (bits) = Sampling Rate (Hz) × Sampling Resolution (bits) × Time (seconds) × Number of Channels (e.g., 1 for mono, 2 for stereo).
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If you double the sampling rate of an audio file, what happens to its file size?
The file size will also double, assuming all other factors (resolution, duration, channels) remain the same.
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What is the difference between Sampling Rate and Bit Rate?
Sampling Rate (Hz) is how often a sample is taken. Bit Rate (bits per second) is the total amount of data used to represent one second of audio. Bit Rate = Sampling Rate × Sampling Resolution × Channels.