Spatialisation and surround sound

Question 1

How have the ears of humans and animals evolved?

Answer 1

• Humans (and animals) have evolved
 to be binaural (have two ears), enabling
them to detect where a sound is
likely to be coming from.
• Having two sources
of sound information
allows the brain to
 triangulate where
the sound originated.

Question 2

What do humans and animals use the difference in level to determine?

Answer 2

A sounds rough direction

Question 3

How does the mass of the head act like a baffle?

Answer 3

The mass of the head 
creates an acoustic
 shadow that attenuates 
the level in one ear, 
acting like a baffle.

Question 4

How does the head also help to determine the sound source?

Answer 4

Like any baffle, the head reduces some frequencies more than others (e.g. high frequencies), thus
 providing even more information to help determine the source.

Question 5

How does the pinna filter incoming sound?

Answer 5

The pinna subtly filters 
sounds from the rear…
(especially high-frequencies) while focusing
 sound from the front
 into the ear canal.
- This allows us to
target distant sounds
 by orienting our head.

Question 6

Give an example of early spatialisation methods.

Answer 6

Richard Wagner’s Bayreuth Theatre (1876) - Purpose-built venue for Wagner’s ‘Ring Cycle’.
- Orchestra seated behind a screen, arranged to hide the players and balance the sound, allowing Wagner to control how the music was transmitted to the audience.

Question 7

What were the speakers like for ‘talkies’ in early film sound?

Answer 7

In early film sound, (“talkies”) voices would appear to
come from the cinema’s single speaker, which may
not be near the image of the speaker on screen.

Question 8

How were live music performances in cinema different?

Answer 8

Live music performances envelope the audience in sound from multiple sources:

• Performers and instruments at different locations
• Complex reflections off the surrounding walls

Question 9

Who pioneered stereo recording?

Answer 9

Stereo recording and playback was pioneered in the early 1930’s by Alan Blumlein, working for EMI.

Question 10

Give 4 innovations that Blumlein introduced with stereo.

Answer 10

• The coincident X-Y (or “Blumlein”) pair arrangement for mics 
(for recording stereo sound)
• Recording two grooves on records (e.g. vinyl).
• Stereo disc-cutting head
• A transformer to matrix left and right (sum and difference)

Question 11

How did early recordings make overt use of stereo?

Answer 11

Sounds were positioned as the band appeared on stage

Far L/R (Drums/Bass), Centre (Lead), Far R/L (Rhythm Guitar)

Question 12

How were early stereo recordings not ‘mono’ compatible?

Answer 12

Centre would appear louder when played back in summed mono or completely cancelled if the speakers were out of phase.
- Hence, studios recorded both mono and stereo versions.

Question 13

How do modern recordings make more conservative use of stereo?

Answer 13

• Conservative panning
• Must be suitable for radio, portable audio, night clubs, etc.
• Stereo image used to subtly separate sounds in a mix
or add spatial effects, texture, atmosphere, or depth.

Question 14

Linear pan law: what is the formula for L and R?

Answer 14

• L = 1-x

- R = x

Question 15

What is an issue with the ‘phantom centre’?

Answer 15

• Listener must be equidistant between speakers for centre effect.
• If not, speech may not seem to originate from the image of the actor.

Question 16

What is a common solution for issues with the phantom centre?

Answer 16

• Centre speaker used for dialogue (and on-screen) sounds.

- Left-Centre-Right (LCR) is a common post-production mix format.

Question 17

Describe the early cinema sound of ‘Cinerama’

Answer 17

• Developed in 1950’s.
• 3 projector panoramic image.
• 7 discrete channels of audio.
  (5 behind widescreen, 2 rear surround speakers)
• Live sound engineer does fading.

Question 18

When was Dolby stereo first introduced?

Answer 18

With Star Wars in 1977

Question 19

What did Dolby stereo use a matrix to encode?

Answer 19

4 virtual ‘tracks’ on 2 analog channels (stereo)

Question 20

Why is a subwoofer (0.1) used?

Answer 20

We are not easily able to localise
 low-frequency sounds, so a single
subwoofer can be used to deliver 
all low frequency sounds, meaning
 that satellites don’t have to.

Question 21

How are cinema sound systems laid out?

Answer 21

3 speakers behind screen (L, C, R)
Many speakers on side and back walls
- Split Left/Right Surround in 5.1.
- Split Left/Right Side + Left/Right Back in 7.1