Jefferson Scholars Foundation 2018 Electronic Music Workshop | April 25th, 2018

What is Sound?

The sounds we here are the result of compressions (squishing together) and rarefactions (pulling apart) of air molecules within a longitudinal pressure wavefront from some sound source (such as a cello or speaker or mouth).

 
 Sound travels through a longitudinal wave in a medium (usually air).

Sound travels through a longitudinal wave in a medium (usually air).

 

We can describe characteristics of sounds produced by periodic (repeating) waves with the following terminology:

  1. Amplitude (pressure intensity) - how loud the sound is
  2. Frequency (speed/wavelength) - how high or low the sound is
  3. Phase (only matters if we have multiple periodic sounds) - the temporal relationship between the waves

What is Electronic (or Electro-Acoustic) Sound?

Electronic (or electro-acoustic) sound is when these compressions and rarefactions are produced by a speaker, which creates sound waves by displacing air by moving back and forth in its casing in response to an electrical signal. Similarly, a microphone works via the reverse process: changes in the pressure around the microphone displace a diaphragm whose movement is turned into an electrical signal.

 A speaker producing a sound wave.

A speaker producing a sound wave.

 
 A microphone picking up a sound wave and turning it into an electrical signal.

A microphone picking up a sound wave and turning it into an electrical signal.

 

How Can We Record Sound?

The act of recording sound is done by recording the analog electrical signal output of a microphone onto a medium. This medium could be analog: magnetic tape or wire, vinyl, cassette, 8track, etc. or digital: CD, flash drive, computer hard drive, etc. When recording onto a digital medium, the analog electrical signal output of the microphone must be converted to digital data via a process called analog-to-digital conversion (ADC).

<Discuss sample rate and bit depth>

To play back a digital audio file we need to take the digital data and turn it back into an analog electrical signal that can drive the speakers, which is done via a process called digital-to-analog conversion (DAC).

What are the Best Practices for Sound Recording?

When recording sound you don't want the sound to be too quiet (needing to be boosted, and boosting the noise inherent in the medium along with it) or too loud (distorting, irreparably damaging the sound wave you are trying to record). To make sure you are recording with the correct levels you can use headphones to hear exactly what your recording will sound like or keep an eye on the recording level display that sound recorders have.

 
 The two horizontal bars (labelled L and R) show the current stereo microphone amplitude.  The numbers along the bottom (-48, -32, etc. up to 0 on the right) show the current sound pressure level (SPL) in decibels (dB). A healthy recording hovers around -12dB.

The two horizontal bars (labelled L and R) show the current stereo microphone amplitude.

The numbers along the bottom (-48, -32, etc. up to 0 on the right) show the current sound pressure level (SPL) in decibels (dB). A healthy recording hovers around -12dB.

 

Recording Assignment

With a partner, a portable recorder, and headphones go record 3 close sounds and 3 distant sounds. Be back in 20 minutes.

How Can We Edit Sound?

To edit sound on a computer the sound must first be imported to the computer's hard drive by connecting the recorder to the computer and transferring the recorded sound files. You may then open these sound files in a sound editor or digital audio workstation (DAW). The DAW we will be using is Reaper (download here).