iSpectrum Analyzer Manual
iSpectrum is an easy to use audio spectrum analyzer that allows the user to view live audio in a standard frequency plot, a stereo oscilloscope view and a waterfall display. The user can adjust the display resolution, center frequency and save images to disk.
iSpectrum requires a live audio input device (microphone or line in).
Features...
Requirements
Controls
Selecting
the Waterfall button switches the display to the
Waterfall and audio Spectrum views.
Selecting the Oscilloscope button switches the display
to the Oscilloscope view.
Waterfall view, in which a one pixel high line is added
to the bottom for each FFT plot that is shown in the FFT view
below it. The display scrolls up as each entry is added. The
lighter the color the stronger the corrisponding signal. To
determine the frequency of any pixel on the waterfall view,
enable grid lines by checking the Grid Lines
check box. Also you could enable the Frequency Marker
and using the left and right arrow keys move the marker over to
the signal of interest to get an accurate frequency reading.
Using you mouse and click on the FFT plot also causes the
frequency marker to move to the point of you choosing.
FFT view displays an FFT plot of data from the audio
input device you select using the Input device
popup. The audio is always sampled at 44.1Kz and run through an
FFT. The size of the FFT is determined by the bandwidth you
select using the Bandwidth slider.
The window popup allows you to select what windowing function is
applied. (see below)
The Input channel popup allows you to select which audio channel
(Left/Right) is used to collect the audio samples that are to be
plotted.
When the samples have been run through the FFT it can be plotted
as is by selecting Standard from the plot popup. If you
would like to see a Normalized plot (a plot in which everything
is plotted relative to the highest signal) then select Normalized.
When the Normalized plot is selected, the Input Gain
slider is disabled.
The Pause button allows to freeze all views.
The Average popup allows you to plot the
average of 2, 4, or 6 FFT samples. This can help eliminate a
good deal of noise from the displayed plot.
The Input Gain slider can only be used when the plot
popup is set to standard and the input device has volume
controls. This slider amplifies or attenuates the sampled audio
signal. The amount of attenuation or amplification possible is
determined by the input device you are using.
The Filter button causes the Filter Drawer and filter
center frequency marker to appear.
The Input device popup allows you to select which audio
input device data is captured from.
The Output
device popup allows you to select which audio output device the
data is sent to after passing through the filters if Pass
Through is enabled.
The Freq. Marker checkbox controls the display of the
frequency marker. The frequency marker can be moved by using the
left or right arrow keys. The marker can also be moved by mouse
clicking on a point of interest in the FFT view. Midway on
marker is displayed the frequency and relative db value.
The Play Through checkbox allows you to send the
filtered audio to an output device (speaker etc.)
The Source popup controls the display of the grid line
overlay.
The Faster CPU check box allows to reduce the load on
your system. This is useful if you have an older/slower system.
When you uncheck this option the program only FFTs and plots
every third block of samples.
The Bandwidth slider allows you to select the bandwidth
resolution of the display, the options are 1, 2, 5, 10, 20 and
40 hz /pixel.
The Center Frequency slider allows you to shift the view so that a selected frequency is at the center of the display.
Filter Drawer Controls
The Enable check box turns the selected filter on or off.
The Filter popup selects the type of filter to apply: Low Pass, High Pass, Band Pass or Notch.
In signal processing, a digital biquad filter is a second-order recursive linear filter, containing two poles and two zeros. "Biquad" is an abbreviation of "biquadratic", which refers to the fact that in the Z domain, its transfer function is the ratio of two quadratic functions.
High-order recursive filters can be highly sensitive to quantization of their coefficients, and can easily become unstable. This is much less of a problem with first and second-order filters; therefore, higher-order filters are typically implemented as serially-cascaded biquad sections (and a first-order filter if necessary). The two poles of the biquad filter must be inside the unit circle for it to be stable. In general, this is true for all filters i.e. all poles must be inside the unit circle for the filter to be stable.
The Frequency slider adjusts the center frequency of the Notch and Band Pass filters and the cutoff for the High Pass and Low Pass filters.
The Bandwidth slider adjusts the width or "Q" of the filters.
FFT WIndowing Functions
Wikipedia
Reference
In
signal processing, a window function (also known as an
apodization function or tapering function) is a mathematical
function that is zero-valued outside of some chosen interval.
For instance, a function that is constant inside the interval
and zero elsewhere is called a rectangular window, which
describes the shape of its graphical representation. When
another function or waveform/data-sequence is multiplied by a
window function, the product is also zero-valued outside the
interval: all that is left is the part where they overlap; the
"view through the window". Applications of window functions
include spectral analysis, filter design, and beamforming. In
typical applications, the window functions used are non-negative
smooth "bell-shaped" curves, though rectangle, triangle, and
other functions can be used.
iSpectrum is FREE!
If you find iSpectrum useful, please consider donating something towards it's support costs. Thanks!