Representing sound: sampling rate

The idea

Sampling rate is the number of samples of a sound wave captured each second, measured in hertz (Hz). A sound wave is continuous, so a computer stores it by measuring the wave's amplitude at regular time intervals; the sampling rate fixes how many of those measurements happen per second. A rate of 44 100 Hz means 44 100 amplitude readings every second. A higher sampling rate records the wave's shape more closely, so the digitised sound is more faithful to the original, but it creates more data because more samples must be stored. A lower rate captures fewer points, so detail is lost and the sound may be less accurate. Sampling rate is distinct from sample resolution, which is the number of bits used to store each individual sample's amplitude. To answer a question on sampling rate, identify that it concerns how often samples are taken per second and that it is measured in Hz.

What earns the marks

• Sampling rate is the number of samples taken per second from a sound wave.
• A higher sampling rate captures the wave shape more accurately, giving a more faithful recording.
• A higher sampling rate increases the amount of data stored because more samples are taken.
• Sampling rate is different from sample resolution, which is the bits per sample.

Common mistakes and how to put them right

• Confusing sampling rate with sample resolution.

  Put it right: Sampling rate is samples per second (Hz), whereas sample resolution is the number of bits per sample.

• Thinking a higher sampling rate reduces file size.

  Put it right: More samples per second means more data, not less.

• Believing sampling rate is measured in bits.

  Put it right: It is measured in hertz (Hz).

Exam tips

• Link the term to its unit, hertz, to show you understand it is a per-second quantity.
• When comparing rates, state the effect on both accuracy and file size.
• Keep sampling rate and sample resolution clearly separate in your answer.