Representing sound: res = sample resolution

The idea

In the sound-size formula, res stands for sample resolution: the number of bits used to store each single sample of the sound wave. Higher resolution means more bits per sample, so each amplitude value is recorded more precisely and the file is larger. For example, if res = 16, every sample occupies 16 bits. When calculating file size, multiply resolution (bits per sample) by sample rate (samples per second) by seconds, then divide by 8 to convert bits to bytes. Recognise that res is measured in bits, not hertz or seconds, and that doubling res doubles the bit size for the same rate and duration.

What earns the marks

• Res denotes sample resolution, the number of bits stored per individual sample.
• Resolution is measured in bits per sample, not in hertz (that is the sample rate) or seconds (that is duration).
• A higher resolution records each amplitude more precisely and increases file size.
• In the size formula, resolution in bits is multiplied by sample rate and seconds, then divided by 8 for bytes.

Common mistakes and how to put them right

• Confusing res with sample rate.

  Put it right: Res is bits per sample; sample rate is samples per second in hertz.

• Treating res as a time in seconds.

  Put it right: Seconds is a separate term in the formula.

• Forgetting to convert bits to bytes.

  Put it right: Divide the bit total by 8 to give bytes.

Exam tips

• State the unit of res as bits per sample when asked to define it.
• Link a larger res to both greater accuracy and a larger file size.
• In calculations, keep res in bits until the final conversion to bytes.