Tektronix 070-8811-08 - Manual (Page 59)

Reference
44 764 Digital Audio Monitor User Manual
always indicated by the peak segment, so actual headroom is always
visible.
With VU ballistics, the Test Level should correspond to the same
level as above (–18 dBFS) if program exchange is important. In
accordance with standard practice, the Test Level (“line–up level”)
corresponds to 0 VU, so you may set the 0 dB mark to the Test
Level. If program material is then peaked at 0 dB, you can expect
actual peaks to be 8 to 14 dB higher (which can be easily seen with
the true peak indicators of the 764). A good setting for the Peak
Program Level would be in the range of –8 to –10 dBFS. IEEE
152–1991 recommends that the VU meter readings of program
material be 8 dB below those of a PPM meter to get the same actual
program level. The above setup accomplishes that.
All of the above is for standardizing digital recordings or digital
transmissions for international program exchange. Individual
organizations may have their own internal standards. Some
experienced recording engineers prefer a higher alignment level than
–18dBFS to make fuller use of the available coding range for a better
S/N ratio. Others are more conservative. For example, SMPTE (in
RP 155–90) recommends a “reference” level of –20 dBFS.
And, of course, digital purists may always select True Peak ballistics.
In-Bar Warning Messages
The in-bar warning messages (for example, INPUT UNLOCKED, in
the Channel 3 and 4 meter bars in Figure 32) are listed below in
order of error condition priority. Higher priority errors preempt lower
priority ones. Messages — or “Flags” — are displayed for as long as
the error condition lasts plus n seconds, where n is the CLIP/MUTE
hold time set through the Level Meters submenu (see page 52). The
INPUT UNLOCKED and LOW CONFidence flags will always
appear in both bars of the affected input; all other messages can
appear in one or both bars, depending on channel content.
INPUT UNLOCKED —The 764 is not locked to an incoming signal on
the indicated input channel. Data cannot be decoded; all data and all
other errors are ignored. This message will appear when no input
signal is present.