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CD ROM Paradise Collection 4
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CD ROM Paradise Collection 4 1995 Nov.iso
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gram.zip
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README.TXT
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1994-09-02
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SPECTROGRAM
1. PRINCIPLES OF OPERATION
Most ordinary sounds are complex combinations of individual frequency
components or harmonics which cover a wide frequency range and vary in
intensity over time. A spectrogram is simply a plot of the frequency content
of such an audio signal as a function of time. In this program, digital audio
recordings (.wav PCM format) are analyzed to produce a plot of frequency
versus time, with harmonic intensity represented by a variable color scale.
These spectrograms reveal the fascinating hidden frequency structure of audio
signals and can be used for identifying or classifying particular sounds.
When used to analyze recorded voice, spectrograms have also been know as
'voice prints'.
2. SYSTEM REQUIREMENTS
Spectrogram will run on any Windows 3.1 equipped machine. However,
the intensive calculations required to develop the frequency spectrum demand
the fastest processor available. A 80486 DX or better processor is
recommended. While the program will run on an 80386 and/or without a math
coprocessor, it may be painfully slow. In addition, large sound files will
require much memory for analysis and display, so the more memory the better.
3. COMPUTING AND DISPLAYING A SPECTROGRAM
Choose 'Open' from the 'File' menu to select a .wav file for analysis.
If you select a proper file, computation will begin immediately and fill the
screen from left to right with the spectrogram plot. Once computation is
complete, you can scroll long spectrograms horizontally using the scroll bar
at the bottom of the display. The spectrogram display will cover a frequency
range of 1/2 the digital sampling rate. That is, if your file was sampled at
22KHz, the spectrogram display will have a vertical scale of 11KHz. You can
read out the frequency (in Hz) and time (in MSec) for any feature on the
display by clicking the mouse pointer at that spot. A cross-mark cursor will
be set, and readouts of frequency and time at that point will be shown at the
bottom of the display.
You have a choice of a color or gray scale display of harmonic
intensity. Make your selection from the 'Palette' menu.
If you have a windows compatible sound card installed, you will also
be able to play back the spectrogram by clicking the 'Play' or 'Play Wdw'
buttons. The Play button plays back the entire length of the .wav file, while
the Play Wdw button plays back only that portion of the spectrogram which is
visible on the screen.
Also with a sound card installed, you will have the ability to record
digital audio directly to memory. Select 'Record New' from the File menu
to select recording parameters and begin recording. When recording is
complete, computation of the spectrogram will begin. You can save the
recorded digital sample as a .wav file by selecting 'Save As' from the file
menu.
4. DISPLAY THRESHOLD
Display threshold can be set by menu selection to eliminate unwanted
background clutter on the spectrogram display. Ordinarily, a 'Low' threshold
is used. However, if your digital sample has unwanted background noise such
as recording hiss which overwhelms the spectrogram display, select a threshold
of 'Medium' or 'High' to eliminate the clutter.
5. SAMPLING RATE CONSIDERATIONS
Contrary to popular opinion, higher sampling rates are not always
necessary for high fidelity recording. The choice of sampling rate depends
entirely on the highest frequencies in the audio signal. The rule of thumb is
to use a sampling rate that is twice the highest frequency in the audio signal.
That is, if you expect to have no frequency components above 11KHz, then a
sampling rate of 22KHz is adequate. If you examine a spectrogram and see that
all of the signal is concentrated in lower frequency components at the bottom
of the display, then it is a good bet that the recording was sampled at too
high a rate, wasting a significant amount of memory.
The 'Magnification' menu options are provided to solve the problem of
digital recordings which have been sampled at too high a rate. If your
spectrogram shows that all of the frequency components are concentrated at the
bottom of the display, then select a magnification of 'Two' to recompute the
spectrogram at half the recorded sampling rate. The spectrogram will be
computed using every other sample in sequence, effectively cutting the sampling
rate in half. Likewise, a magnification of 'Four' effectively divides the
sampling rate by four. The magnification options are useful for expanding the
detail visible in the spectrogram plot when the original sampling rate was not
matched to the highest frequencies found in the recording. Magnification
should not be used if the spectrogram already shows high frequency components,
since sampling at too low a rate will produce a distorted spectrogram due to
aliasing of frequency components.
6. PROBLEM REPORTING
Programs can only be improved if users provide feedback to the author.
I can be reached at the following addresses for you to report any bugs or to
provide comments or feedback. I encourage anyone with a question to contact
me at :
DELPHI - RSHORNE
COMPUSERVE - 75121,2131
INTERNET - RSHORNE@DELPHI.COM
7. DISTRIBUTION
Spectrogram is Copyright 1994 by R.S. Horne and may be distributed
as freeware.