Engineering Design NIDisk Podręcznik Użytkownika Pobierz pdf (Strona 19)

NIDisk User Guide

During simultaneous acquisition/playback, only the acquisition progress screen is displayed.

Elapsed Time Display

The meter shows elapsed acquisition or playback time graphically via a real-time linear bar

display and numerical readout. See the figures.

Headroom Display

The meter shows peak signal level graphically via a real-time linear bar display, similar to an

LED-based VU meter on a recording console. See the figures.

Like a VU meter, the display is oriented towards headroom, the parameter of greatest

concern to the recording engineer. Headroom is the dB difference between peak signal level

and the overload level of the A/D converter. Overload level is the converter's maximum

positive code, e.g., +2047 and +32767 for 12-bit and 16-bit converters, respectively. When

headroom decreases to 0, the input signal will be distorted in the A/D.

Headroom is also reported numerically. The operator can monitor display color for an

overview of headroom status and can use the numerical readout to adjust system gain

precisely, so as to maximize the signal-to-noise of the recorded signal without risking

overload distortion.

Display Refresh

During recording, the program updates the entire display every 100 msec, reporting the

worst-case headroom during that interval. Refresh interval represents a tradeoff between a

more responsive meter and system loading at very high sample rates. It may be user-

configurable in a future version.

Meter Color Display

The headroom bar changes color dynamically to indicate headroom status, as illustrated in

the figures:

• Green = sufficient headroom: headroom > 6 dB

• Yellow = low headroom: headroom < 6 dB but > 0

• Red = overload: headroom = 0

Here is the meter during recording with sufficient headroom represented by a green bar:

1 2 ... 14 15 16 17 18 19 20 21 22 23 24 ... 35 36

Brak uwag

Engineering Design NIDisk Podręcznik Użytkownika Strona 19