Frequency and pitch

Question 1

What is frequency?

Answer 1

The rate at which a regular event or vibration recurs in Hz.

Question 2

What is the voice band for intelligible speech?

Answer 2

300 Hz to 3kHz

Question 3

What frequencies surround sub bass?

Answer 3

Up to 60 Hz

Question 4

What frequencies surround bass?

Answer 4

60-250Hz

Question 5

What frequencies surround the mid-range?

Answer 5

250Hz-2kHz

Question 6

What frequencies surround the high mids?

Answer 6

2kHz–6kHz

Question 7

What frequencies surround the high frequencies?

Answer 7

6kHz-20kHz

Question 8

What are low frequencies used in?

Answer 8

Used by synthesisers (LFOs), performers (vibrato, tremolo)

Question 9

What is most real world sound made up of?

Answer 9

Multiple frequency components called partials.

Question 10

What do pitched musical sounds contain?

Answer 10

A series of partials with frequencies that are integer relations of each other, called harmonics.

Question 11

What is the fundamental frequency?

Answer 11

The lowest frequency in the harmonic series.

Question 12

What is an overtone?

Answer 12

Any resonant frequency above the fundamental frequency.

Question 13

Which harmonics does a saw wave contain?

Answer 13

All harmonics (1,2,3,4,5,6,7,8,…) in decreasing amplitude

Question 14

Which harmonics does a square and triangle wave contain?

Answer 14

Only odd harmonics (1,3,5,7,9,…)
 in decreasing amplitude

Question 15

How do the frequency and time domains differ?

Answer 15

The frequency domain considers audio from the perspective of frequency, rather than time - As opposed to the time domain (waveform) where we view audio as amplitude variations over time.

Question 16

What can the frequency domain be used for?

Answer 16

Can be used to analyse, plot, process, or even store audio information (e.g. MP3).

Question 17

What else can the frequency domain reveal details about?

Answer 17

Pitch and timbre 
(tone color / tone quality, e.g. piano, violin, etc.) - Plots often complex / difficult for humans or computers to interpret (e.g. automatic transcription)

Question 18

What did Joseph Fourier propose?

Answer 18

• Any complex periodic signal could be represented as the sum of an infinite number of simple tones (i.e. sine waves of different frequency and amplitude)
• Complex sounds can be broken down
 into constituent frequency components

Question 19

How can you ‘re-synthesise’ a sound?

Answer 19

Knowing all the (possibly infinite) frequency components of a sound, you could theoretically use a corresponding number of sine wave sound generators to re-synthesise it.

Question 20

What does resynthesis allow you to do?

Answer 20

This allows us to change the frequency components independently
of time (without affecting the duration of the sound).

Question 21

What is pitch shifting?

Answer 21

Changes the pitch of audio without altering
 the duration (e.g. auto-tune, auto-harmonization)

Question 22

What is time stretching?

Answer 22

Changes duration (e.g. tempo) without altering pitch.

Question 23

What are vocoders?

Answer 23

They exploit the synthetic-sounding result of resynthesis as a musical effect.

Question 24

Describe a spectrum analyser.

Answer 24

Very short segments used to provide a realtime animation
 of frequency bands. Can be useful for EQ’ing.

Question 25

Describe a spectrum plot.

Answer 25

Analyses a longer segment of audio for precise frequency content, at the expense of time information.

Question 26

Describe a waterfall plot.

Answer 26

• A Waterfall plot is a three-dimensional (3D) projection of time vs. frequency vs. amplitude.
• It combines both 
time and frequency
 domains.

Question 27

Describe a spectrogram.

Answer 27

Plots time vs. frequency, using colour (or greyscale) to indicate the amplitude of frequency components.

Question 28

What is pitch?

Answer 28

A subjective, perceptual quality of sound. It is based on pattern matching - recognising patterns of frequencies (rarely just one). Fundamental frequency of a harmonic indicates pitch.

Question 29

Physiology of the ear: Pinna?

Answer 29

large area to receive and focus sound energy; collects sound… like a gramophone horn

Question 30

Physiology of the ear: Auditory (or ear) canal?

Answer 30

Acts as a closed tube resonator, enhancing frequencies in the range 2-5 kHz (e.g. speech).

Question 31

Physiology of the ear: Timpanic membrane (ear drum)?

Answer 31

Vibrates in sympathy with incoming sound … like a gramophone’s diaphragm.

Question 32

Physiology of the ear: Ossicles?

Answer 32

Bones of the 
inner ear connecting the 
ear drum to the cochlea;
 transmitting / amplifying
 a stream of vibrations …
like a gramophone stylus.

Question 33

Physiology of the ear: Cochlea?

Answer 33

Converts
 vibrations to frequencies
sent as electrical nerve
impulses to the brain …
like an electric pickup

Question 34

What is the unit that measures loudness?

Answer 34

Phon

Question 35

What represents the interval of an octave?

Answer 35

A ratio of 1:2 between two fundamental frequencies or (8ve).

Question 36

What is consonance related to?

Answer 36

How ‘harmonious’ a note interval is (e.g. perfect 5th (2:3) or perfect 4th(3:4)).

Question 37

How many cents are there in a semitone?

Answer 37

There are 100 cents in a semitone

- Therefore there are 1200 cents in an octave (octave is divided into 12 equal steps or semitones)