The key to understanding how the front panel and software meters relate is in the signal flow. The levels at the BoB inputs and
outputs of the view file are the same levels displayed on the front panel meters, although they are calibrated differently. Once
the signal is processed, digital audio levels inside the DPU should be monitored exclusively within the view file using software
meters. This is because there is an additional 12 dB of headroom, or gain, available exclusively within the DPU. This additional
gain cannot be displayed on the front panel meters. Before the signal leaves the DPU at the BoB output block, it should be
attenuated back to full-scale converter level, or lower, to avoid clipping the D/A converter.
Refer to the above example. The Full-Scale Input Sensitivity switch is set for +18 dBu and a +18 dBu signal is coming into the
MM-8802 (0 dB, or full-scale, on the front panel input meter). The first software meter, placed at the view file input block, will
indicate this level as +23.0 dB peak. The +23.0 dB represents the full-scale peak level, measured inside the DPU. Inside the
DPU, there is an additional 12 dB of headroom available for EQ, summing, etc. This headroom level is represented by a 12 dB
boost at the first Level control and the peak meter connected to it indi35.0 dB (max DPU level). The signal is then
attenuated by the second Level control to avoid clipping the MM-8802 and its peak meter again shows +23.0 dB. This signal
level will be output via the BoB output block, and returned to the MM-8802 at full-scale. The front panel output meter will
display 0 dB, regardless of the position of the Full-Scale Output Drive switches.
This +23.0 dBu level represents 0 dB on the front panel meters. Remember, the +23.0 dB DPU level is always the maximum full-
scale level that can be received by, or sent to the MM-8802. Anything above +23.0 dB (DPU level) that is sent to the BoB out-
put block, and thus, to the MM-8802’s D/A will be clipped. The additional 12 dB of headroom is only available within the DPU.
MM
™
-8802 User Manual
Page 18
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MediaMatrix
®
, Meters & the MM-8802
Inside the DPU audio levels are represented by software based meters that can be placed into the signal flow at any stage. They
can also be found within certain devices and can be configured as input or output meters. These meters include a bar-graph
display for quick visual reference. However, the more accurate way to monitor levels is by using the small text display included
with each meter. This display will give you exact readings with much finer resolution than the bar-graph display.
It is very important to understand that the software meters display actual levels inside the digital domain (DPU). Even though
the front panel meters are in the digital domain, they can only display the digital signal immediately after the A/D and before
the D/A converters. In the view file, this same signal shows up at the BoB input and output blocks. Once the signal is
processed, split or distributed by other audio devices, the only way to accurately meter the signal is by placing software meters
within the view file signal flow. The relationship of the hardware and software meters is shown in the following illustration.
(See pages 20-21 for details on software controls.)
Analog to Digital
Converter
Front Panel
Input Meters
Full-Scale = 0 dB
(Full-Scale In)
(Gain/Headroom)
MM-8802
DPU
(Full-Scale Out)
Front Panel
Output Meters
Analog
Gain Stage
Digital Control
Digital to Analog
Converter
Analog
Gain Stage
Output
Drive Level
Input
Sensitivity
TX
INPUT
OUTPUT
RX
