Many people do not have the money
to buy an expensive Oscilloscope or a Spectrum Analyzer. Or simply they do not
want to invest money for something they will use rarely. Nevertheless many
people love to build and test audio amplifiers or other kinds of simple circuits
(oscillators, filters, etc); or simply they need monitoring some particular
signal (an output of a sensor), and are only interested in the range of audio
frequencies . A lot of musicians, for example, need a spectrum analyzer with an
octave band analysis tool embedded.
So, a good soundcard
could be all the hardware they need. Together with their PC, that is, a lot of
hardware already available at no cost. A recent soundcard with a sampling
frequency of 96 or even 192 Khz will allows to manage signals with frequencies
up to 96Khz ( well beyond the audio frequencies) transforming VA in a powerful
set of instruments for general electronics and other applications. VA is useful
anywhere you need a true oscilloscope, spectrum analyzer, frequency meter,
voltmeter, function generator and even a distorsiometer (only THD for now). For
example when tuning a class B power amplifier: you need a spectrum analyzer (or
a THD meter) to minimize the crossover distortion...
The idea of using the soundcard of
a PC is not a new one (there are many of programs like VA) but I tried to write
a program specifically made for the analysis of audio circuits for the
electronics hobbyist. I think VA is probably less "extravagant" than other (i.e.
less windows and frills) but full of substance and even a lot of original ideas.
I’ve been working on
VA for five years; VA is a software “under construction”, and so continuously
I’ve new ideas and often new release are ready to download.
VA has the unbeatable capacity to
perform a full real time Digital-Analogue conversion for the oscilloscope
function, although rarely it is well understood.
Consider using a frequency
sampling of (standard) 44100 Hz, with a 16 bit resolution (resolution is not
relevant for the purpose of the discussion below...).
Other programs similar to VA simply plot the raw points on the screen, which
means you can’t easily analyze signals with a frequency higher than 3000/5000 Hz
(there are limited points to plot). As an example, think a sinusoidal signal of
20 KHz. You would have only two points (more or less) per each complete
sinusoidal cycle! The Nyquist theorem says that it is quite sufficient to
RECONSTRUCT the signal, that is, to re-compute also ALL the points between that
two points. Standard software normally use only that two points, simply
connecting them by means of a line…try to see what happens if you draw a 20 Khz
sine with only two points for cycle, without recomputed all the points: it will
appear like a triangular waveform... Try the power of VA enabling the function
"full D/A", apply a sinusoidal signal of 15-20 KHz (for example using the
Waveform generator included in VA) finally use the "Time division" control for
the selected channel (mS/d) to display the signal at the desired detail level.
You will see a perfect waveform with all the points of the original signal (not
only two).
Another powerful feature of VA is
its Waveform generator; it uses only band limited algorithms, avoiding aliasing
in waveform generation. Aliasing in waveform implies the generated waveform are
completely unusable.
VA is also simply to
use; launch the install program, and install VA in a path of your preference;
select the input source, by means of the “Volume Control” of windows or, better,
by means of the listbox “input source” of VA (upper right corner of the command
bar of VA. Command bar: it is under the “caption” of the main window).
Then click the “on” button (always on the command bar). You can select the most
options of VA directly from the main window. ALL the remaining commands and
setup option are contained in the “settings” windows, that you can invoke always
with the command bar (button “setting”). An English help should be available
for each window, but it is still under construction.
Latest VA reviews, articles:
Send an e-mail to
alfredo[at]accattatis.org for questions and/or suggestions about the web
site. The webmaster is Alfredo Accattatis.
Last modified:
28-mar-2014