Sound and listening

What is sound

We experience sound thought displacement of air molecules from a source to a the receiver.

When a source emits a sound, it makes the air molecules compress and decompress, traveling away from the source.

The rate of this compression-decompression variation is what is called the frequency of a sound. And the amount of air molecules displace give us the amplitude or volume of a sound.

Sound wave properties

• frequency = pitch
  • measured in Hertz (Hz) or cycle per second. 1Hz = 1cycle/sec
• amplitude = volume
  • measured in decibel (db)

Sound waves on liquid

audible sound

Human audible sound, or the hearing spectrum, is located between 20Hz and 20 000Hz of of the acoustic spectrum

How do we listen?

How does the movement of air molecules gets perceived as sound?

Spacial Perception Sound

How do we detect the position where sound is coming from?

• arrival time difference
• amplitude difference
• filtering, by the outer ear

Janet Cardiff - binaural mics

Hearing as composing

Recording and listening exercise.

• record 1 to 2 minutes of sound
• write down all you here during those minutes, either with or without headphones

4'33

4'33 (1952) is a probably the most famous John Cage composition, where the performance stands in front of the audience without playing a single note, for 4 minutes and 33 seconds.

http://hyperallergic.com/85779/the-original-john-cage-433-in-proportional-notation-19521953/

• hearing as composing
• all sound can become music

Expanded listening

contact mics

• listen to how solid objects respond to vibration
• due to its physical properties each object will respond - resonate - differently to vibration
• The resonant frequencies are the frequencies that are emphasized by the object

David Tudor - Rainforest (1968)

• http://composers-inside-electronics.net/rainforest/rainforest/RAINFOREST.html
• https://www.youtube.com/embed/iT9HP48sHTg
• http://www.getty.edu/research/tools/guides_bibliographies/david_tudor/av/rainforest.html
• Holzer, Derek, and Mads BEch Paulszewski. n.d. “Rainforest 2012.” http://macumbista.net/files/rainforest_overview.pdf

Electromagnetic pickups

Instead of capturing acoustic waves, like acoustic microphones, electromagnetic pickups capture electromagnetic fields.

Christina Kubisch Electrical Walks explore cities electromagnetic fields.

• http://www.christinakubisch.de/en/works/electrical_walks
• http://cabinetmagazine.org/issues/21/cox.php
• https://www.youtube.com/watch?v=5tCphr8pbFk

Digital audio

Audio is stored digitally discretely (in segments or sample) as opposed to a continuous analogue process

http://www.synthgear.com/2014/audio-gear/record-grooves-electron-microscope

More grooves: http://sessionville.com/articles/vinyl-through-the-microscope-looking-glass

Two parameters are essential to digital audio:sampling rate and bit rate

sampling rate: how frequently the analogue signal is sampled File:Discrete-signal.png

The sampling rate of CDs is 44.1KHz, that means that discrete samples of an analogue signal have been stored 44100 times each second. Digital video cameras tend to store audio at 48KHz.

bit rate: accuracy of sampling - how many values are used to represent the amplitude of a signal

The bit rate of a CD is 16-bit, that means that 2¹⁶ (65536) values are used to encode the audio digitally

• 8 bit 2⁸ (256) values

Bibliography

• Collins, Nicolas. 2006. Handmade Electronic Music. London: Routledge.
• “Sound:An Interactive eBook on the Physics of Sound.” 2017. Sound: An Interactive eBook on the Physics of Sound. Accessed January 11. https://soundphysics.ius.edu/.