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
- Launch VA
- 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)
- 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.
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