Club Amiga de Montreal - CAM/CAM_CD_1.iso/files/369a.lha/SeeHear/SeeHear.readme

Text File | 1990-04-09 | 5.2 KB | 112 lines

SEEHEAR INTRODUCTION

SeeHear does frequency spectrum analysis of sampled sounds.  It
displays a graph of frequency in hertz (cycles per second) on the
horizontal axis and time on the vertical.  Successive time slices
of the sound are analyzed, and at each frequency the loudness
determines the pixel color.  This type of analysis if commonly
call a spectrogram.

GETTING STARTED

To run the program, double-click its icon.  Don't be confused the
the details of the control window which opens, just select Open
from the File menu and pick a sound file (a DEMO_SOUND file is
included).  SeeHear recognizes IFF 8SVX format files, although
any file can be interpreted as sound.  SeeHear will read and play
the sound before opening a 32 color 320x200 screen for analysis,
so be sure to have your sound volume turned on.

Some lengthy number crunching is involved especially at startup,
so be patient.  SeeHear will slice out a short piece of sound
(0.1 s or so), play it, and scan across one line displaying its
color-coded frequency spectrum.  The 30 display colors are shown
in 2 columns at the right, brighter colors for louder sounds.

We perceive frequency as the pitch of a sound, and a steady pitch
will result in a vertical line.  Because of harmonics, even a
single musical note will produce several lines; more complicated
sounds produce more complex patterns.

ANALYSIS SCREEN GADGETS

SeeHear analysis may be interrupted by toggling the halt/freeway
gadget at the upper right.  Seehear only checks for events after
each line of analysis, and so will probably not respond
immediately.  Once halted, one can play the sound with the
loudspeaker gadget.  Sound playing is controlled by three arrows
at the right of the graph, for start, select, and end.  These
arrows are moved by selecting with the left mouse button down and
releasing within the graph area.  The latest arrow touched is
hilited in green, and controls the play mode.  Start hilited
plays through to end, select hilited plays only the selected
line, and end hilited plays through like start but with clicks to
set off the selected line.  Moving the select arrow also causes a
crosshair mark to be placed on the graph, with a readout of time
and frequency in the title bar.  This readout includes a zoom of
the 3x3 pixels at the crosshair, and bars in the color scale
indicating the 3 pixels across the selected line.  The frequency
readout can interpolate between pixels.  A file scroll gadget on
the far right allows different segments of the input file to be
analyzed.  A window switching gadget takes SeeHear back and forth
between the analysis screen and the control window on the
Workbench screen.

Playing the selected line only also outputs data for that line to
file ram:SeeHear.temp; see the source for details.  This can be
used to make ordinary line graphs of the spectrum, etc.

CONTROL WINDOW

A control window on the Workbench screen allows many options to
be adjusted.  Gadgets are outlined in boxes to distinguish them
from information and text.  The file format gadgets allow an IFF
file to be analyzed as RAW if one wants to change the sampling
rate for example.  Byte offsets for time zero (t0) and analysis
start can be specified (t0 not with IFF).  Sample rate in hertz
is specified for RAW files.  SeeHear uses the Fast Fourier
Transform (FFT) algorithm, and takes slices that are a power of 2
in length.  The FFT produces half as many frequencies as time
samples; since the graph uses 256 pixels for frequency, several
frequency steps may need to be averaged into one pixel, or just
the lower frequencies are displayed.  Multiple pixels per
frequency sample are also allowed, especially for short FFTs.
Frequency annotation is both in hertz and musical notes using the
12 semitone chromatic scale based on a specified middle A.
Successive time slices usually step ahead less than the length of
the FFT because of the need to smoothly fade in and out of the
time slices to avoid analysis artifacts.  Spacing of timing lines
and annotation can be controlled.  Smoothing uses a gaussian
curve whose width is specified relative to the time step as an
envelope to select the time slice for analysis so that clicks at
the ends are avoided (these result in spurious frequencies).  A
large width effectively disables smoothing.  Frequency amplitudes
are mapped into 30 colors with either a logarithmic (decibel, dB)
or linear (%) scale.  When selecting a point for frequency
readout on the analysis screen, SeeHear will search for a peak
amplitude over (possibly) several pixels to enable interpolation.
The sound can optionally be played before analysis, and also each
time slice during analysis.  A window switching gadget permits
going back and forth with the analysis screen.  The bottom of the
control window is a message area.

MENU

The File/Open item brings up a file requester for the input sound
file.  Once selected, analysis begins immediately, so any options
must be changed before opening.

File/Quit has the same effect as the close gadgets.

Control/Restart begins analysis using a previously opened file.

AUTHOR

SeeHear was written and is copyright 1989, 1990 by

     Daniel T. Johnson
     2654 E. 25 St.
     Tulsa, OK  74114

and is freely distributable for non-commercial use only.