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| DETAILED OPERATING INSTRUCTIONS
PDM
PDM Operator's Manual Version 2.4a • September 2019
Select a value between
+20dBu
and -
10dBu
to result in fullscale within PDM and on the
digital output.
The bottom line of the display shows current Left and Right internal levels in dBFS. This is
the result of the incoming analog signal, adjusted by the second line of the LCD and sent to
the analog-to-digital converter. Typically, these should read –12 for a +4 dBu lineup tone.
For most installations, where 0 VU = +4 dBu, we recommend setting the analog
Input
sensitivity
to
+14dBu=0dBFS.
Analog
Output Level
Shown when analog or digital inputs are selected. The LCD will
look like this:
Input
Sens.
(Sensitivity) The LCD will look like this:
Input Sens.
+14dBu=0DBFS
“‘ Chg Value OK√
L:
-
70 R:
-
70 CNCL#
Current value is +14 dBu: this should be the absolute loudest analog
signal PDM will see in your installation.
Press
¨
or
Î
to change the input sensitivity.
L
and
R
show the resulting digital levels for analog signals coming into
PDM. You can use these readings with an external test tone, to verify
Sensitivity settings.
Select a value between
+20dBu
and -
10dBu
to result in fullscale within PDM and on the
digital output.
The bottom line of the display shows current Left and Right internal levels in dBFS. This
is the result of the incoming analog signal, adjusted by the second line of the LCD and
sent to the analog-to-digital converter. Typically, these should read –12 for a +4 dBu
lineup tone
1
.
For most installations, where 0 VU = +4 dBu, we recommend setting the analog
Input
sensitivity
to
+14dBu=0dBFS.
Analog
Output Level
Shown when analog or digital inputs are selected. The LCD
will look like this:
Output Level
0DBFS=+14dBu
“‘ Chg Value OK√
L:
-
70 R:
-
70 CNCL#
This shows how the analog output level reflects digital audio levels within
PDM’s processor. In this example, 0 dBFS inside PDM will cause a +14
dBu analog output. This particular setting is equivalent to the “0 VU =
+4 dBu” standard, with 10 dB of headroom.
Precise Left and Right output levels are displayed in dBFS
Select a value between -
10dBu
and
+20dBu
to appear at the analog outputs, when
PDM’s internal digital signal level is 0 dBFS. This is usually set to match the Analog In-
put sensitivity, so our recommendation for most facilities would be
0dBFS
=
+14dBu
.
However, you can use other settings if you want PDM to also create analog audio gain
or loss. Note that during Bypass mode, any such gain or loss is also bypassed: the out-
put equals the input.
The analog outputs are always active, even if a digital input has been selected.
Don’t confuse dBu—an analog measurement—with digital dBFS!
Analog dBu is a comparison to an arbitrary voltage (.775 v), and signals can be
much hotter. A console’s output is typ4 dBu (1.228 v) when the meter reads 0 VU,
but that’s for a sinewave test signal. Peaks in voice waveforms, in real-world broadcasting,
can sometimes be considerably above that... even though properly-calibrated VU meters are
deliberately too slow to register them. Analog is very forgiving of these momentary peaks.
However, in the digital world, 0 dBFS (decibels referred to Full Scale) is an absolute
ceiling. Some devices distort horribly or crackle when an input attempts to pass this value.
1
The +14 dBu sensitivity in the figure would make these meters read –10 dBFS with a st4 dBu line level
test signal. In other words, the setting means a +14 dBu signal would read 0 dBFS—the maximum allowable
digital signal—and standard line level is 10 dB less than that, or –10 dBFS.
Select a value between -
10dBu
and
+20dBu
to appear at the analog outputs, when PDM’s
internal digital signal level is 0 dBFS. This is usually set to match the Analog Input sensitivi-
ty, so our recommendation for most facilities would be
0dBFS
=
+14dBu
. However, you can
use other settings if you want PDM to also create analog audio gain or loss. Note that
during Bypass mode, any such gain or loss is also bypassed: the output equals the input.
The analog outputs are always active, even if a digital input has been selected.
Don’t confuse dBu—an analog measurement—with digital dBFS!
Analog dBu is a comparison to an arbitrary voltage (.775 v), and signals can be much hotter.
A console’s output is typ4 dBu (1.228 v) when the meter reads 0 VU, but that’s for a
sinewave test signal. Peaks in voice waveforms, in real-world broadcasting, can sometimes
be considerably above that... even though properly-calibrated VU meters are deliberately
too slow to register them. Analog is very forgiving of these momentary peaks.
However, in the digital world, 0 dBFS (decibels referred to Full Scale) is an absolute ceiling.
Some devices distort horribly or crackle when an input attempts to pass this value. PDM
handles overloads differently, applying serious limiting to gracefully protect your signal
(and listeners).
If your facility uses the +4 dBu standard of modern broadcast equipment, our
recommended setting of +14dBu= 0dBFS provides 10 dB of headroom for protection while
still maintaining an 84 dB signal-to-noise ratio. With this setup, it’s unlikely that PDM will
ever go into distortion or audible limiting.
If you’re dealing with heavily-processed feeds you can use a lower setting; for seriously
dynamic performances it may need to be higher. PDM has 94 dB dynamic range at all
settings, within 2 dB of the theoretical limit for 16-bit sound.
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