How sound is stored

In this lesson

Explain that sound is analogue and must be sampled to be stored digitally, define a sample, the sampling rate, the sample resolution or bit depth and the sample interval, and describe how the sampling rate and the number of bits per sample affect playback quality and file size - using the name your own board uses.

What it covers

• Sound is ANALOGUE and must be converted to a digital form for storage and processing (AQA 3.3.7a's own wording)
• What a SAMPLE is: a measure of AMPLITUDE at a point in time (AQA's scope; Edexcel names amplitude in its statement)
• SAMPLING RATE: the number of samples taken in a second, measured in hertz - 1 hertz is 1 sample per second
• SAMPLE RESOLUTION (AQA) is BIT DEPTH (OCR and Edexcel): the number of bits per sample. ONE QUANTITY, TWO NAMES, and the bridge must be on screen with the board badges attached
• SAMPLE INTERVAL (Edexcel only): the time between one sample and the next - the other side of the rate, and Edexcel examines the difference
• DURATION (OCR only): how many seconds of audio the file contains
• What more bits per sample actually buys: more different amplitude values that a sample can be, so the measurement is closer to the real height - NOT more samples
• The effects, qualitatively and in both directions: a higher rate or more bits per sample means better playback quality AND a bigger file

Key words

On the specification