Rane RPM 26v - Manual (Page 14)

Manual-14
OUTPUT TRIM
The Output Trim looks, feels and acts in
much the same way as the Input Trim. So,
read the Input Trim section on the previous
page for basic operating instructions. The two
Trims differ by the location on the screen, the
single
Output Meter, the Link functionality
and, most importantly, their purpose. The Output Trim’s
purpose is to provide up to 30 dB of attenuation on each
output. This is useful to adjust for speaker sensitivity in both
distribution and crossover applications where each output may
require a different level. Use the
Mute button to turn indi-
vidual outputs off.
The Output Trim controls a VCA attenuator which
maintains output dynamic range over a wide range of attenua-
tion settings. Even though the screen shows the Output Trim
before the Limiter and the D/A converter, the VCA is after
the D/A converter internally. However, the unit operates as if
the Output Trim control were before the D/A and the Limiter.
Since the RPM 26v knows the analog Output Trim attenua-
tion, the Limiter Threshold is internally and transparently
adjusted to keep audio operation as displayed. Therefore,
what you see is what you get. The Output Trim’s detail
window is shown here:
The Output Meter
displays the voltage
level at the output
screw terminal of the
RPM 26v in dBFS if the
Master Output Lvl is
set to
0 dB. Add the
Master Output Level to
each Output Meter
Level to get the level at
the unit’s output. The
Mute button mutes the
given output. The
Invert
check box inverts the
polarity of the given
output. When ramping
is enabled, each time
the
Invert box is
changed the given
output’s level ramps to
off , the polarity is inverted and the level ramps back up.
Many people frown upon purposely inverting the polarity of
an audio signal. The invert function here is provided solely as
a convenient tool for testing polarity. In permanent installa-
tions it is always wise to correct polarity inversion problems
through other more permanent or “hardware” means such as
correcting cable-wiring errors.
The Link selection box “ties” groups of output Trim
controls together. There are 4 possible groups, None, 1, 2 or
3. None in the selection box indicates the given output is tied
with no other output. If two outputs’
Link boxes share a
common value, for example 1, then those two output trims are
linked together.
A/D, D/A AND METERING
Now, a word about metering and our
pal, the Windows operating system.
Displaying meters on computers poses a
unique problem for software designers and
sometimes for users, especially if you have
a “slow” computer. Everyone is familiar
with analog meters without computers deciding that display-
ing meter indicators needs to wait until a “more important”
task is completed. Windows provides the RPM 26v software
an update window opportunity every 100 milliseconds (10
times per second). And, since there are more than just meters
to update, other functions at the computer’s discretion can
have a higher priority than the meters. This simply translates
into “the more meters you have on the screen, the more
sluggish and inaccurate they will appear.” For this reason, it
is wise to adjust the RPM 26v
Trim controls or view its
meters one at a time. This displays the least number of meter
indicators on the screen, making the display’s update rate as
reliable as possible.
The A/D and D/A blocks on the RPM 26v Device Edit
screen indicate where in the signal chain the A/D and D/A
conversions occur. These blocks also contain the signal
present and overload indicators, all of which default to single,
two-color indicators: green for signal present, red for over-
load and gray for no signal detected.
Double clicking on any of the A/D or D/A blocks
turns the block into an eleven segment meter. On the
A/D block, these meter segments correspond to every
third segment from the
A/D (dBFS) meter. The
segments on the D/A block also correspond to every
third segment from the Output meter. The top seg-
ment lights at -2 dBFS, each subsequent segment lights 3 dB
before the segment above it. Again, to keep the meters as
reliable as possible, keep as few meter segments on the screen
as possible when adjusting levels.
The RPM 26v’s front panel Input signal present LEDs are
familiar analog implementations. The remaining meters —
the input overload and all output meters — are microproces-
sor controlled but have a guaranteed update rate of 90
milliseconds, or just over 11 times per second. The peak level
of the audio samples within that 90 ms are displayed.
MASTER OUTPUT LEVEL
The Master Output Level operates all six output VCAs
simultaneously, while keeping the Output Trims the same
relative to one another. The Output Trim and the Master
Output Level operate the same VCA, but they are otherwise
independent. Therefore, the overall attenuation of a given
output is the sum of the attenuations of the Output Trim and
the Master Output Level. This control does not affect the
Output Meter or the Limiter Threshold. When setting the
Limiter, the Master Output Level must be taken into account.