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)