Natural Science Forum / Physics / Acoustics / July 2005

The first and third are the same - graphs of amplitude against time. I
don't know what the second is. The final graph is spectrum against
time. It is also sometimes called a sonogram.

These are all produced as standard features of DAW (digital audio
workstation) programmes, such as Adobe Audition.

d

Pearce Consulting
http://www.pearce.uk.com

    The first three are plain ordinary oscilloscope traces (or analog
equivalent) or time-amplitude graphs of the sound pressure level (SPL).
Could be sound particle velocity, depending on microphone type used, but
99 our of 100 mics these days are pressure microphones.

    The second graph seems to be a running o.358 second digital average of
the frequency content of the last graph.

    The last graph is a time/frequency/intensity trace. The vertical axis
is the sound frequency... usually 0Hz to 5,000 or 10,000 Hz. The
analysis method is most often today a fast fourier transform (FFT). at
each frequency (vertical axis) and time (horizontal axis) the brightness
or intensity of the pixel laid there  is proportional to the amplitude
(usually amplitude squared, absolute value, or rectified envelope of
that wave amplitude).

    This latter process has often been called "Voice Print", and is often
sold under many other names.

    An analysis program that will generate the same FFT display on your PC
screen for any .WAV file you have is GRAM.EXE written by and available
from Bob Horne (rshorne@delphi.com).

        Angelo Campanella