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Visual Analyser for Windows


A brief introduction


By Alfredo Accattatis


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.


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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