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)