NAME

       jaaa — JACK and ALSA Audio Analyser

SYNOPSIS

       jaaa [-h]  [-C nchan]  [-J]  [-A   [-ddevice]    [-rrate]    [-pperiod]    [-nnfraqs] ]

DESCRIPTION

       jaaa is an audio signal generator and spectrum analyser designed to make accurate measurements.

OPTIONS

       -h        Show summary of options.

       -C        Number of channels (1..8) [4

       -J        Use JACK

       -A        Use ALSA (with following options)

       -d device Alsa device [hw:0.0]

       -r rate   Sample frequency [48000]

       -p period Period size [1024]

       -n nfrag  Number of fragments [2]

       Either -J or -A must be given.

INTERACTIVE CONTROL

   Input :
       Select on of the four inputs.

   Frequency and Amplitude :
       These two sets of buttons set the display view.  One of these six buttons, or 'Bandw', 'Peak', or 'Noise'
       discussed below, has an orange LED at its left side.  The LED indicates the 'currenty selected parameter'
       that usually can be modified in three ways :

          •  by typing a new value into the text widget, followed by ENTER

          •  by using the '<' or '>' buttons to decrement or increment,

          •  by mouse gestures

   Frequency :
       Buttons 'Min' and 'Max' set the min and max displayed frequencies.  If either of these is selected then

          •  a horizontal Drag Left changes 'Min'

          •  a horizontal Drag Right changes 'Max'

       Button  'Cent'  is  the  frequency at the middle of the x-axis.  Button 'Span' is 'Max' - 'Min', changing
       this value preserves 'Cent'.  If either of these is selected then

          •  a horizontal Drag Left changes 'Cent'

          •  a horizontal Drag Right changes 'Span'

       Button 'Cent' can also be set by Clicking in the frequency axis scale.

   Amplitude :
       Button 'Max' is the maximum value on the y-axis.  Button 'Range' is the range of the y-axis.   If  either
       of these is selected then

          •  a vertical Drag Left changes 'Max'

          •  a vertical Drag Right changes 'Range'

       So for the last four mouse gestures, a Drag Left will scroll the display, while a Drag Right will zoom in
       or  out.   Maybe  I  will  add  and  automatic  selection of the axis based on the direction of the mouse
       gesture.

   Analyser :
       The analyser is based on a windowed FFT.  Actually the windowing is performed by  convolution  after  the
       FFT,  and  combined with interpolation.  The windowing and interpolation ensure that displayed peaks will
       be accurate to 0.25 dB even if the peak falls between the FFT bins.  More accurate  measurements  can  be
       made using the markers (see below).

       Button 'Bandw' sets the FFT length, and hence the bandwidth of the analyser.

       Depending  on  this  value,  the  size  of the display and the frequency range, you may sometimes see two
       traces.

       This happens when the resolution of the analyser is better than the display, so that one  pixel  contains
       more than one analyser value.

       In  that  case,  the blue trace is the peak value over the frequency range represented by each pixel, and
       the gray one is the average value.

       The first one is correct for discrete frequencies, and the latter should be used to read noise densities.

       There is no mouse gesture to change the bandwidth.

       Button 'VidAv' or video average, when switched on, averages the  measured  energy  over  time.   This  is
       mainly used to measure noise.  The averaging length increases over time, to a maxumum of 1000 iterations.
       Changing the input or bandwidth resets and restarts the averaging.

       Button  'Freeze'  freezes  the analyser, but not the display, so you can still scroll and zoom or use the
       markers discussed below.

   Markers :
       Markers are used in order to accurately read off values in the display.  There can be up to two  markers,
       set  by clicking at the desired frequency inside the display.  When there are two markers, the second one
       will move with each click, while the first remains fixed.  Measured values for the two markers, and their
       difference in frequency and level are displayed in the upper left corner of the display.

       Button 'Clear' clears the markers.

       When 'Peak' is selected, clicking inside the display will set a marker at the nearest peak.

       The exact frequency and level of the peak are found by interpolation, so the frequency can be  much  more
       accurate  than  the  FFT  step, and the level corresponds to the true peak value regardless of display or
       analyser resolution.

       When 'Noise' is selected, clicking inside the display will set a noise marker.

       The noise density (energy per Hz) is calculated and displayed.

SEE ALSO

       jackd (1)

WWW

       http://www.kokkinizita.net/linuxaudio/

AUTHOR

       This manual page was written by Philippe Coval rzr@gna.org for the Debian system  (but  may  be  used  by
       others).   Permission  is  granted to copy, distribute and/or modify this document under the terms of the
       GNU General Public License, Version 2 any later version published by the Free Software Foundation.

       On Debian systems, the complete text of the GNU General Public License can be found in /usr/share/common-
       licenses/GPL.

                                                                                                         JAAA(1)