Digital Sound & Music: Concepts, Applications, & Science, Chapter 2, last updated 6/25/2013
response graph that shows the phase that each frequency component is in. Each of these two
graphs covers the audible spectrum. In Section 3, you‟ll be introduced to the mathematical
process – the Fourier transform – that converts sound data
from the time domain to the frequency and phase domain.
Applying a Fourier transform to impulse response data –
i.e., time represented in the time domain – yields both
frequency and phase information from which you can
generate a frequency response graph and a phase response
graph. The frequency response graph has the magnitude
of the frequency on the y-axis on whatever scale is chosen
for the graph. The phase response graph has phases
ranging from -180 to 180 on the y-axis.
The main points to understand are these:
A graph is a visualization of data.
For any given instance of sound, you can analyze the data in terms of time, frequency, or
phase, and you can graph the corresponding data.
These different ways of representing sound – as amplitude of sound over time or as
frequency and phase over the audible spectrum – contain essentially the same information.
The Fourier transform can be used to transform the sound data from one domain of
representation to another. The Fourier transform is the basis for processes applied at the
user-level in sound measuring and editing software.
When you work with sound, you look at it and edit it in whatever domain or
representation is most appropriate for your purposes at the time. You‟ll see this later in
examples concerning frequency analysis of live performance spaces, room modes,
precedence effect, and so forth.
2.2.6 Ear Testing and Training
If you plan to work in sound, it‟s important to know the acuity of your own ears
in three areas – the range of frequencies that you‟re able to hear, the differences
in frequencies that you can detect, and the sensitivity of your hearing to relative
time and direction of sounds. A good place to begin is to have your hearing
tested by an audiologist to discover the natural frequency response of your ears.
If you want to do your own test, you can use a sine wave generator in Logic,
Audition, or similar software to step through the range of audible sound
frequencies and determine the lowest and highest ones you can hear. The range
of human hearing is about 20 Hz to 20,000 Hz, but this varies with individuals
and changes as an individual ages.
Not only can you test your ears for their current sensitivity; you also can train your ears
to get better at identifying frequency and time differences in sound. Training your ears to
recognize frequencies can be done by having someone boost frequency bands, one at a time, in a
full-range noise or music signal while you guess which frequency is being boosted. In time,
you‟ll start “guessing” correctly. Training your ears to recognize time or direction differences
requires that someone create two sound waves with location or time offsets and then ask you to
discriminate between the two. The ability to identify frequencies and hear subtle differences is
Aside: WAV and AIFF files
store audio as amplitude
information in the time domain,
while MP3 files store audio as
spectral data in the frequency
domain. Both methods are able
to capture the sonic information
for playback later on.