Introduction To Visual Analyser

 

 

Introduction

Visual Analyser is free audio analysis software, written by Italian engineer and enthusiast, Alfredo Accattatis.  As you will see below, it is extremely powerful, but that makes it a little hard-to-follow.  I plan a series of tutorials to take newcomers through the extraordinary range of facilities it offers.

It occurs to me that those who will most benefit from this software are people who currently don't have test equipment.  That will include people who have never used this sort of test gear before.  So we'll discuss along the way how the software can be used, as well as how to use it.

In this first tutorial, we'll have VA create a test signal, and view it in both the Time and Frequency domains (the oscilloscope and spectrum views).  And we'll have a quick look around to see the remarkable range of other things VA can do.  I'd suggest printing out this short tutorial so you can devote all the screen to VA.


Download, unzip and install the software:

  • Go to: 2012 Beta version of VA.

  • Click Log in as Guest (no registration required)

  • Click Latest VA version

  • Click on VA2012beta.zip.  Software will download.

  • Extract to a convenient folder.  C:\Program Files\VA might seem appropriate.


Preparation

Connect the Line Output of your soundcard back to the Line Input connector.  (This is sometimes called Loopback.)  If your Line Output connector is also the Speakers connector, use an adapter or clip leads to connect it to both the speakers and the Line Input.  We want to be able to hear what we are seeing.


Create the test signal

  1. Launch VA
  2. Press the WaveOn button (middle of screen, extreme right)

Sound should now be coming from your speakers.  It should sound pure.


View the test signal in the Time Domain (Oscilloscope)

  1. Start the analyzer by pressing ON, in the top left corner.

In the upper screen you should now see the test wave, in the familiar oscilloscope view.  Amplitude is vertical, time is horizontal.

Note that we are seeing only one channel, while VA has two.  We'll bring in the second channel in a later article.  We'll also see how to change the settings.


View the test signal in the Frequency Domain (Spectrum Analyser)

In the lower screen, you see a spectrum analysis (or FFT, Fast Fourier Transform) of the test signal.  Ideally our test signal should take the form of a single peak at its frequency, 1kHz.  Depending on the quality of your sound card, you might also see harmonics, at 2, 3, 4 etc kHz, spurious artifacts at other unrelated frequencies, hum at power line frequency or its multiple and background noise or "grass" along the bottom.  The more the spike stands out from the rest, the lower the distortion and noise your soundcard is achieving.  You may be able to correlate unwanted byproducts on the screen with those you hear in the speakers.


A quick look around

We'll finish this introduction with a quick look around some of the other VA features, activated by the tick boxes at the right of the lower (FFT) screen.

  • Tick Voltmeter.  A window opens to tell us the voltage of the incoming signal.  Don't believe it just yet; it's uncalibrated.  We'll look into calibrating it in a later tutorial.  You could already use it for relative measurements though (e.g. louder than).
  • Tick Freq Meter.  Another window opens to tell us the frequency of the test signal.  We can trust this, as no calibration is needed for frequency.
  • The Wave Gen tick box opens a window that gives a clue to the vast power of the built-in signal generator.  We'll spend a lot of time on this later.
  • The Phase meter will illustrate the relative phase of signals as they pass through circuitry.  Probably won't make much sense just yet.
  • Tick the THD box and a value for the Total Harmonic Distortion appears in the FFT screen.  Hopefully, it's very low!
  • Similarly, the "THD & Noise view" tick box gives the current value for THD and noise combined.  In other words, a convenient measure of everything that ideally shouldn't be there.
  • The ZRLC tick box takes us to a whole new panel and a whole new world.  No longer are we measuring signals, we now have the ability to measure real things resistors, capacitors, inductors and impedances.  We do have to build a simple test rig, but we'll discuss that later.
  • The Recorder tick box opens a familiar tape recorder interface.  We can record, save, load and play back signals later.
  • Press the Capture Scope button at right of screen.  You can use this to save an image of the Scope screen to file.  Close the window.
  • Press the Capture Spectrum button at right of screen.  You can use this to save an image of the Spectrum and Phase screens to file.  Close the window.
  • Using the traditional oscilloscope to take measurements, you had to count squares and multiply by the X or Y calibrations.  Not so in VA.  Press Values, just to the right of the Scope screen.  A column opens at the edge of screen to give us a range of useful measurements at much higher precision that the old method could ever offer.
  • The Filters button, top of screen, opens a panel inviting us to restrict the full measurement width available in our sound card for special purposes. 
     

Woah, sensory overload!

I think this is a good time to pause and reflect on what we've seen. 

VA isn't just a signal or function generator, or an oscilloscope, or a spectrum analyzer, or an AC millivoltmeter, or a Noise and Distortion analyzer, or a phase meter, or a frequency meter, or indeed a ZRLC bridge.  It's all these things a complete audio electronics laboratory, kindly made available for our use for free!  Thanks, Alfredo!

And we're already well on the way to being able to use it in real-world situations.  We've generated a test tone, and viewed it in both the time and frequency domains.  We've seen how we will be able to use it to measure level, frequency, noise and distortion, conveniently and accurately.  By simply including a device like a preamplifier in the cabling between input and output of the sound card, we will be able to see any degradation and measure the qualities of that device.  No more guesswork!

A package this big will take a little bit of understanding to get the best out of it.  We hope this series of tutorials will help you achieve that with maximum ease and minimum confusion.  Further tutorials will appear here as I delve deeper into the program.


Talk to me!

Please contact me at terry@mcgee-flutes.com if you find problems with any of these tutorials or would like to suggest improvements.

 


On to Visual Analyser - Oscilloscope,

or Back to McGee-flutes Index page...

Created 20 May 2012