OS/2 Shareware BBS: Science/Science.zip/fftpm110.zip/english.INF

OS/2 Help File | 1996-10-21 | 11KB | 247 lines

ΓòÉΓòÉΓòÉ 1. Program description ΓòÉΓòÉΓòÉ

FFTPM Fast Fourier Transformation for audio signals

General Information:

o What is FFTPM ?
o FFT-Fast Fourier Transformation
o The Frequency spectrum
o About this program
o History
o About the autor
o Thanks to
o OS/2-Producs


ΓòÉΓòÉΓòÉ 1.1. What is FFTPM ? ΓòÉΓòÉΓòÉ

FFTPM is a program for the OS/2 Presentation Manager for analysing audio
signals and showing their Frequency spectra. It is a simple spectrum analyser.

The signals are Fast-Fourier-Transformed and its spectrum will be displayed in
a line graph.

There are many possible applications for this program, e.g.: harmonic
distortion analysis or simple playing with sounds and spectra.

System requirement is a 16bit soundadapter, that is used by MMPM/2. Line-In or
a microphone can be used for input.


ΓòÉΓòÉΓòÉ 1.2. FFT-Fast Fourier Transformation ΓòÉΓòÉΓòÉ

The Fourier Transformation is an algorithm, used in this program, to calculate
the frequency spectrum from the audio signal.

To be exact, it is the Discrete Fast Fourier Transformation (Fast Fourier
Transformation = FFT) which is best used for computers. The FFT calculates the
Fourier-coefficients for a sampled, periodic signal. These coefficients are
similar to the signal strength at a specified frequency.

This program uses a fast swap-algorithm, that was translated from FORTRAN to C.


ΓòÉΓòÉΓòÉ 1.3. The frequency spectrum ΓòÉΓòÉΓòÉ

All periodic signals in the time domain, e.g.: audio signals, can be described
through a sum of harmonic sinusodial waves. That means, all sounds can be
mathematical described by a number of foundamental waves.

A violin sound for example, has a foundamental and many harmonics. The
frequencies of the harmonics are always a multiple number of the foundamental.
A clear sinusodial tone has exactly one foundamental frequency and no
harmonics.

Every amplifier produces harmonic distortions, caused by internal
nonlinearities. It is possible to determine these distortions (THD) by using a
low-distortion sinus wave generator and measure the output signal with a
spectrum analyzer. This method has its limitations when using PC soundadapters,
because they produce noise and distortion itself. It is possible to check the
soundcards distortion by connecting it directly to a low noise generator and
check the spectrum.


ΓòÉΓòÉΓòÉ 1.4. Aliasing effect ΓòÉΓòÉΓòÉ

This effect describes the appearence of frequencies, which are higher than the
Nyquist frequency, as lower frequencies in the spectrum. This can happen, if
there are high frequent signals and the Nyquist filter can not remove them.

Frequencies in the Spectrum, which should be normally displayed above the
Nyquist limit are mirrored below the limit. This can cause problems to
interprete the spectrum.


ΓòÉΓòÉΓòÉ 1.5. Nyquist filter ΓòÉΓòÉΓòÉ

When sampling a signal in the time domain, it is necessary to filter
frequencies, which are higher than the half sample rate (Nyquist frequency). If
it is not possible to prevent this, aliasing effects will occur. High quality
soundcards have good working filters, but it is possible that these filters can
also attenuate also the lower frequencies.


ΓòÉΓòÉΓòÉ 1.6. About this program ΓòÉΓòÉΓòÉ

Thank you for testing FFTPM!

FFTPM is free for private use. There are absolutetly no warranties. The author
is not responsible for damages in any case!

If you like FFTPM or not, the Author would appreciate very much if you send him
an eMail or a postcard. :-)

FFTPM has been developed with the WATCOM C/C++ compiler version 10.0a and the
IBM WARP-Toolkit.

Thanks to:


ΓòÉΓòÉΓòÉ 1.7. History of FFTPM ΓòÉΓòÉΓòÉ

24 Aug 1996 - Version 1.0 first public uploads, only in german language
20 Sep 1996 - Internal release with minor corrections for the window routines
30 Sep 1996 - Version 1.10 first english version, installation script, resources in DLL

To do:

Speed improvement using DART
THD-analysis


ΓòÉΓòÉΓòÉ 1.8. About the author ΓòÉΓòÉΓòÉ

FFTPM is my first freeware OS/2-program. It would be very nice to send me a
note if you think this program is useful. Depending on this resonance, I will
make further developements and improvements.

Dipl.-Ing. JБrgen Dittmer
Technologiezentrum GKSS
Max-Planck-Straсe, GebДude 1
D-21502 Gessthacht
Germany
Tel.: [phone] and [phone]
Fax.: [phone]
eMail: [e-mail]
WWW: http://wave.gkss.de
FTP: wave.gkss.de

OS/2 products


ΓòÉΓòÉΓòÉ 1.9. OS/2 product announcement ΓòÉΓòÉΓòÉ

Watchdog for OS/2

The Watchdog for OS/2 is a ISA-plug-in card that can detect a hanging system
and reboot it, if necessary. The device driver has the ability to watch up to
32 processes. The Watchdog is predestinated for stand alone systems, such as
servers or process controllers.

At the moment 2 different Watchdog-cards are supportet. For more information,
look at http://wave.gkss.de or send a mail to the author.


ΓòÉΓòÉΓòÉ 1.10. Many thanks for tests and support! ΓòÉΓòÉΓòÉ

Bill Sutton, for the  MM-playlist tips
Ralf Tralow for Testing
Many people from (de.)comp.os.os2.* -newsgroups


ΓòÉΓòÉΓòÉ 2. Program menus ΓòÉΓòÉΓòÉ

Description of the program settings


ΓòÉΓòÉΓòÉ 2.1. FFT ΓòÉΓòÉΓòÉ

Samples

Select a number of samples for the FFT. As more samples are calculated, as more
spectral lines are displayed. Note that the calculating of the FFT will take a
longer time with a higher number of samples.

Window function

The window function is a weigth function for the input signal. Every window
form folds its ows characteristic spectrum to the result and gives a different
output. If no window is used explitcitly, we have a rectangular window. The
differences in the window functions are mainly in the signal near- and far
range resolution.


ΓòÉΓòÉΓòÉ 2.2. Sample rate ΓòÉΓòÉΓòÉ

Number of values per second for digitizing the input signal. The spectrum can
be displayed until the half sample rate (Nyquist-Limit). The highest frequency
in the input signal must be below the Nyquist-Limit. See also: Aliasing-Effects
and Nyquist-Filter


ΓòÉΓòÉΓòÉ 2.3. Display ΓòÉΓòÉΓòÉ

Hold-Off time

Time in seconds to freeze the screen until the next spectrum will be
calculated.

Log

If this box is checked, a logarithmic scale will be used for the amplitude.

Output is always referenced to the maximum peak. That means, the highest value
is always 100% or 0dB (decibel).


ΓòÉΓòÉΓòÉ 2.4. Input ΓòÉΓòÉΓòÉ

Simulation

Selection of calculated time functions :

 Γûá Square wave
 Γûá Periodic pulse
 Γûá Triangular wave
 Γûá Sawtooth wave

Remark: The functions square-, triangular- and sawtooth wave are bandwith
limited to 21kHz. They show interesting aliasing effects in the spectrum if the
sample rate will be reduced.

Sound adapter

Selection of input: Line-In or Microphone.


ΓòÉΓòÉΓòÉ 2.5. Input level ΓòÉΓòÉΓòÉ

The upper bargraph shows the input level of the sound adapter. This value
should be close to, but never reach 100%, because signal peaks may be clipped.

Gain sets the amplification multiplier, Level is for fine tuning.


ΓòÉΓòÉΓòÉ 2.6. End ΓòÉΓòÉΓòÉ

Explination really necessary?


ΓòÉΓòÉΓòÉ 2.7. Help ΓòÉΓòÉΓòÉ

Help for this program


ΓòÉΓòÉΓòÉ 2.8. Ini-File ΓòÉΓòÉΓòÉ

Error message: FFTPM.INI not found.

This message occurs, if the program is started the very first time, when no INI
file was created. It should not appear again.

FFTPM stores its settings and window positions in FFTPM.INI when the user ends
the program. It uses the defaults, if FFTPM.INI was not found.

FFTPM will not write any data to OS2.INI or OS2SYS.INI.