Students should understand that a sample is a measure of amplitude at a…

The idea

When an analogue sound wave is sampled, each sample is a single measurement of the wave's amplitude taken at one specific moment. Amplitude describes how far the wave is displaced from its resting level at that instant, so a loud moment gives a large amplitude and a quiet moment a small one. The sampler reads the amplitude at fixed time intervals set by the sample rate, then converts each reading into a binary number whose precision depends on the resolution in bits. So a sample is not a stretch of sound or a frequency value: it is one amplitude reading tied to one point in time. Plotting many such readings in order rebuilds an approximation of the original wave, and the more frequent and precise the readings, the closer the approximation.

What earns the marks

• A sample is one measurement of amplitude, not a duration of sound.
• Each sample is tied to a specific point in time determined by the sample rate.
• Amplitude is the wave's displacement from its resting level at that instant.
• Each amplitude reading is converted into a binary number using the resolution in bits.
• Many samples in sequence approximate the original analogue wave.

Common mistakes and how to put them right

• Describing a sample as a length of recorded sound.

  Put it right: A sample is a single amplitude value at one instant.

• Confusing amplitude with frequency.

  Put it right: Amplitude is displacement (loudness), frequency is how rapidly the wave repeats.

• Thinking samples are stored as analogue values.

  Put it right: Each amplitude reading is converted to a binary number.

Exam tips

• Define a sample precisely: amplitude measured at a point in time.
• Distinguish amplitude (measured by each sample) from frequency (how often the wave repeats).
• Explain that resolution in bits controls how precisely each amplitude value is stored.