afft(1) afft(1)
Name
afft - A Realtime FFT display client
SYNOPSIS
afft [-color] [-d device] [-file file] [-gain gainvalue] [-length
fftlength] [-log] [-min minvalue] [-max maxvalue] [-nodc] [-noscope]
[-nowindow] [-realtime] [-sine] [-spec] [-stride stridelength]
Description
afft accepts mu-law audio data from one of several sources, executes a run-
ning Fourier transform on the data, and displays the transform result. The
display is updated continuously in either "waterfall" or "spectrogram" for-
mat.
afft is initially configured through command line switches. Many of the
parameters can be changed while the progogram is running via the graphical
user interface, as described below.
The source of the audio that is displayed depends on the configuration as
folows: If the -file switch is given, then the audio source is a file of
mu-law samples. Otherwise, if the -sine switch is given, the audio source
is a "canned" sine wave that sweeps up and down the frequency spectrum. If
neither -file or -sine are given, then afft takes its audio data from the
audio server local input.
Options
-color
Specifies that the display is to be in color. The default is grays-
cale. The color scheme can be changed while afft is running by means
of a pull-down menu labeled "Colors".
-d device
Specifies the name of the audio device. If not given, afft defaults
to the local audio device.
-file file
Input will be taken from file, which should contain raw mu-law samples
of audio data. afft will continuously loop through the file from
beginning to end, rewind the file, and repeat. If file is given as
"-", input is taken from stdin. Since it is not possible to rewind
stdin, afft will terminate on end-of-file in this case.
If afft can connect to the audio server, then the file is played
through the audio output device in synchronization with the fft
display.
-gain gainvalue
Sets the gain in DB to be applied to the audio samples. Should be in
the range of -100 to -5, and represents a level down from a theoreti-
cal peak value of 0DB. Applies only when log mode is selected, see
-log switch. Default value is -20. The gain value may be controlled
while afft is running by a slider labeled "Gain".
-length fftlength
Sets the number of samples over which each FFT transform is computed.
Legal values are 512, 256, 128, and 64. Default value is 512. The
length can be changed while afft is running by means of a pull-down
menu labeled "FFT Length"
-log
Selects the initial display mode to be logarithmic. If not specified,
the initial display mode is linear. The selection between log and
linear mode may be changed while afft is running by a pair of radio
buttons labeled "Log" and "Linear".
-min minvalue
Sets the lowest audio level that will be displayed. Value is in DB
for log mode, or in percent of peak value in linear mode. Default is
-100 in log mode, and 0 in linear. The minimum value may be con-
trolled while afft is running by a slider labeled "Minimum".
-max maxvalue
Sets the hightest audio level that will be displayed. Value is in DB
for log mode, or in percent of peak value in linear mode. Default is
0 in log mode, and 100 in linear. The maximum value may be con-
trolled while afft is running by a slider labeled "Maximum".
-nodc
Supresses display of the DC component. Default is to include the DC
component in the fft display. Inclusion or supression of the DC com-
ponent may be changed while afft is running by a pair of radio buttons
labeled "NoDC" and "DC".
-noscope
Suppresses display of the audio stream in an oscilloscope-like form.
The default is to show this display. Oscilloscope display can also be
turned on and off while afft is running by a pair of radio buttons
labeled "Scope On" and "Scope Off".
-nowindow
Supresses the window function. By default, a Hamming window is used.
Other window functions can be selected through a pulldown menu labeled
"Windows". Additional window functions include Hanning, and Triangu-
lar.
-realtime
If this switch is given, afft attempts to stay synchronized with the
audio server in real time. If afft cannot get enough CPU cycles to
keep up with the incoming audio stream, it may fall behind enough that
it no longer captures valid audio data. In non-realtime mode (the
default), afft will discard audio samples in order to keep up with
real time.
-sine
Causes afft to begin operation in demo mode, which displays a sine
curve sweep from the minimum frequency up to the Nyquist cut-off fre-
quency. afft can operate in this mode even if the audio server is not
running or no audio hardware is available. afft can be switched
between demonstration mode and live mode (input from the audio server)
by a pair of radio buttons labeled "Live" and "Demo.
-spec
Selects spectrogram display. Otherwise, a waterfall style of display
is used. You can switch at will between spectrogram and waterfall by
a pair of radio buttons labeled "Waterfall" and "Spec".
-stride stridelength
Sets the number of samples that afft advances between FFT frames.
Legal values are 512, 256, 128, and 64. Default value is 512. How-
ever, the stride will never be greater than the FFT length (see
above). The stride can be changed while afft is running by means of a
pull-down menu labeled "Stride"
Owner
Original by L. Stewart
User Interface by J. Morse
Copyright
Copyright 1992-1994 Digital Equipment Corporation