Representing sound: sample resolution.

The idea

Sample resolution is the number of bits used to store each individual sample of a sound wave, sometimes called bit depth. When a sound is digitised, the amplitude at each sample point is recorded as a binary value; the sample resolution sets how many bits that value uses. A higher sample resolution gives more possible amplitude values, so each sample is recorded more precisely and the digitised sound is more faithful to the original. A lower resolution gives fewer possible values, so amplitude is rounded to coarser steps and detail is lost. Increasing sample resolution increases the number of bits stored per sample, so the file needs more storage. Sample resolution is distinct from sampling rate, which is how many samples are taken per second. To answer a question on sample resolution, identify that it concerns bits per sample and its effect on precision and data size.

What earns the marks

• Sample resolution is the number of bits used to store each sample.
• A higher sample resolution gives more possible amplitude values, so each sample is more precise.
• A higher sample resolution produces a more faithful recording of the original sound.
• A higher sample resolution increases the number of bits stored per sample, so more storage is needed.
• Sample resolution is different from sampling rate, which is samples per second.

Common mistakes and how to put them right

• Confusing sample resolution with sampling rate.

  Put it right: Resolution is bits per sample, whereas rate is samples per second.

• Thinking a higher sample resolution reduces file size.

  Put it right: More bits per sample means more data.

• Believing sample resolution is measured in hertz.

  Put it right: It is measured in bits.

Exam tips

• State clearly that sample resolution is measured in bits per sample.
• Explain the effect of resolution on both precision of amplitude and storage size.
• Contrast sample resolution with sampling rate so the two are not muddled.