Sound Performance Lab 2711

RackPack: Preference Mic Pre 11

VU Meter

The VU meter displays th e output level of t he preamp. The g auge indi-

cates levels f rom -20 dB to +5 dB. If necessary you can lower the s en-

sitivity by 10 dB so that the ga uge goes up to +15 dB output level (see

“-10 dB” below and “About Leveling” on the previo us page).

The VU meter is cu stom made to meet SPL spec ifications and assures

a balanced optical perception tha nks to it’s optimized ball istics.

An especially interesting f eature is the option to switch between two

display modes: VU mode and PPM mode. The VU mode ( VU=Volume

Unit) displays average le vels, thu s provides informati on on t he over-

all loudness. The PPM mode (PPM =Peak Progra m Meter) display s the

peak levels.

The integ ration time of the display complies with the BBC req uire-

ments. In VU m ode the r ise time up to 0 dB is approx . 300 ms. In PPM

mode the rise time up to 0 dB is abo ut 2 ms and the release tim e down

to -20 dB is at a “slow” 1,5 seconds. This calib ration ensures to disp lay

even short peaks up to about +6 dB since the needle do es not have to

travel the entire distance of the g auge every time.

PPM

The PPM button allows to switch the VU metering charac teristics fr om

VU display m ode (bu tton is deactivate d and not illumina ted) to PPM

display mode (b utton is ac tive and illuminated). A/D converter dis-

play also make use of the PPM mo de. Monitori ng peak le vels is m ost

important to avoid o verloading the conver ter and to pre vent audibl e

distortion. Peak levels are always above the average levels. It may

make sense in most cases to also p ress the -10 dB button to preven t

the needle from getting stu ck on the right side of the gauge .

-10dB

With this button you can change the sensitivity of the VU display. If

you press the -10 dB button (button is illu minated), th e sensitiv ity of

the display i s lowered by 10 dB. W ith the needle f or exampl e at 0 dB,

a value of +10 dB is displayed. Now you can read values of up to +15 dB.

You alw ays have to add these 10 dB to th e displayed values, for

example if you compare thes e values with those of an A/D converter.

Remember that A/D converters show peak levels, not average levels.

For comparison press the PPM but ton to activate the PPM mod e.

Control Elements

VU Meter, PPM, -10 dB

SIG OVL

10 7531035

30 5070 100

5070 100

11.

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