Amplitude and level

Question 1

What does the term ‘amplitude’ refer to?

Answer 1

The magnitude of change in a given property.

Question 2

What does the term ‘volume’ refer to?

Answer 2

The intensity of the audible result of an audio system.

Related to loudness (the perceived magnitude).

Question 3

What does the term ‘gain’ refer to?

Answer 3

• A change in level

- Gain and level are expressed in decibels (dB)

Question 4

What is amplitude represented as in analogue audio?

Answer 4

Voltage - encodes the compressions and rarefactions in the air (as recorded by a microphone or used to drive a speaker).

Question 5

What is level a measure of?

Answer 5

Average amplitude

Question 6

What is RMS and what is it used to calculate?

Answer 6

Root Mean Square is used to calculate level.

Question 7

What is the threshold of pain?

Answer 7

Between 120-140 db SPL

Question 8

Why is the decibel convenient?

Answer 8

The decibel (dB) is convenient since its logarithmic 
nature enables the representation of both large and small amplitude (or power) ratios. (Rarely needing more than three digits)

Question 9

What is normalisation?

Answer 9

A process that maximises the amplitude of a signal, common in digital systems.

Question 10

What does peak normalisation do?

Answer 10

Finds the greatest magnitude and boosts the signal such that this peak touches 0dBFS. The amplitude is simply scaled, so the process is easily reversible.

Question 11

What does RMS normalisation do?

Answer 11

• Finds the average level (RMS)
• Boosts the signal to a new average (e.g. -3dB for music)
• But the higher amplitudes might now peak above 0dB…
  … so dynamic range compression is applied.
• Compression changes the shape of the wave, so is harder to reverse.

Question 12

What are envelopes?

Answer 12

Generalised shapes describing 
average changes in a given property (e.g. amplitude).

Question 13

Why is the timbre of a sound harder to define if the initial transient is cut off?

Answer 13

Many sounds become recognisable according to the first few milliseconds and initial variations in level, pitch/frequency, etc

Question 14

Describe the envelope of a guitar/piano.

Answer 14

Guitars and pianos have:

• fast attack
• no sustain
• exponential decay/release

Question 15

Describe the envelope of a clarinet.

Answer 15

Clarinets have:

• slower attack
• no decay, continuous sustain
• short release