Engineering Design NIDisk Guida Utente Scaricare il pdf (Pagina 24)

DartDisk User Guide

figure shows the effect of a small overload, in which a 1.6-Volt signal is played through a

Dart card with a full-scale output level of 1.55 Volts.

Full-scale input and output levels vary somewhat between individual Dart cards. To avoid

accidental overload, DartDisk assumes the same minimum full-scale level for all cards. Card

variation produces input and output gain errors of < 1 dB. If this error is not significant or

you are not concerned with absolute sound levels, you can skip the remainder of this

discussion.

For example, a Dart card with a nominal full-scale input level of 1.4 Volts and an actual full-

scale level of 1.5 Volts will produce a digitized signal whose amplitude is 1.4/1.5 = 93% of

the true input level. Thus a 1-Volt peak input signal will be digitized (and displayed in

SIGNAL) with a peak level of 0.93 Volts.

Similarly, a Dart card with a nominal full-scale output level of 1.4 Volts and an actual full-

scale level of 1.5 Volts will deliver analog output signals whose amplitude is 1.5/1.4 = 107%

of their nominal output level. Thus a 1-Volt peak signal (created for example in SIGNAL)

would be delivered with a peak level of 1.07 Volts.

Absolute Gain Accuracy

Absolute input gain accuracy expresses the deviation in dB between the digital amplitude

level reported by the Dart card and the analog input level presented to the card for digitizing.

Similarly, output gain accuracy represents the deviation between the digital signal level

presented for playback and the analog output level delivered by the card.

Gain accuracy depends on the manufacturing process and therefore varies slightly between

units. Gain accuracy is another way of expressing the variation in full-scale input and output

levels discussed in "Maximum Input and Output Levels" above. Dart cards have a specified

input and output gain accuracy of

±1.0 dB. Dart cards are currently shipped with an input

gain calibration factor, which can be used to adjust acquired levels when highly accuracte

absolute input levels are required.

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Engineering Design NIDisk Guida Utente Pagina 24