Digilyzer DL1 User Manual
Digilyzer DL1 User Manual
Digilyzer DL1 User Manual
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Measurement Functions<br />
display mode: Giving a better readability the display mode<br />
determines the rapidity of following up the input signal changes.<br />
The available modes are:<br />
• SLOW 3 sec. averaging<br />
• NRM 1 sec. averaging<br />
• FAST no averaging<br />
If averaging is active measurements are smoothed in an exponential<br />
way (exponential time constant) before being displayed.<br />
Application hints:<br />
• Whenever one sample reaches full scale, slight clipping of the<br />
signal is possible so the THD+N value may degrade. Therefore,<br />
try to level the signal so the full scale indication does not<br />
appear.<br />
• An analog to digital (A/D) converter may show the following<br />
errors at the signal conversion:<br />
• The imperfect linearity of the converter adds (hopefully little)<br />
new harmonics to the signal.<br />
• Every analog part generates noise which is added to the<br />
signal during conversion.<br />
• An A/D converter has only a finite resolution (e.g. 16 bit), so<br />
the converter must round each sample value, which results<br />
in an error called quantization noise.<br />
A perfect test signal fed into an ideal A/D converter causes a<br />
THD+N of the digitized signal of theoretically<br />
-N * 6.02 dB - 1.76 dB (N ... bit resolution of the converter)<br />
E.g. a 16 bit converter has a theoretical THD+N of -98.08 dB.<br />
In practice good converters (even 24 bit) do not achieve better<br />
values than -110 dB. With such measurements the input signal<br />
is often the limiting point. To measure THD+N down to -100 dB<br />
a generated sine wave with a THD+N better than -100 dB is<br />
required. Such a sine wave is often generated only by expensive,<br />
special audio analyzing equipment.<br />
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