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1.2 Gain Specifications
1.2.1 Purpose and Philosophy
The purpose of this specification is to define all relevant gain levels in the Bose
Amplification System™ Power Stand and to specify procedures, for how these gains can be
measured.
We'll do this primarily by specifying a "nominal" level at each point. The "nominal" level repre-
sents the desired operating point. This is the level where we anticipate that the bulk of operation
occurs. Wherever warranted we will also do a headroom analysis in order to specify or derive
the maximum acceptable level before a stage clips or overloads.
The gain structure is designed in a way so that there is one point that handles the main system
constraint. This point is the digital limiter inside the DSP. If all levels are "nominal" the system
should just reach full output, the digital limiter should just be starting to work and all other
analog signals (except for the power amp, off course) should still have reasonable amounts of
headroom. This design allows controlling the high-signal behavior of the system completely in
software through the digital limiter and still offers good signal-to-noise properties.
1.2.2 Gains and Signal Levels
First, we need to define some reference levels for all the adjustable controls in the system. For
the "nominal" signal levels, we assume certain settings in those controls, and define the gain of
each adjustable section.
Control
Gain Range
TRIM –
+8dB to +50dB
Microphone
(XLR Balanced Input)
PreAmp
TRIM –Line
-12dB to +30dB (1/4"
PreAmp
Unbalanced Input)
Ch1, Ch2
-40dB to 0dB
Volume
(Remote)
Master
-80dB to +22dB
Volume
(Remote)
Table 1. Adjustable Controls: Gain range and nominal settings
Next we define all the nominal signal levels for full power output. All signal levels are specified in
dBV unbalanced unless otherwise noted. All levels in front of the DSP can be measured as such
directly. The post-DSP peak output levels can only be observed when the limiter is switched off.
THEORY OF OPERATION
Nominal
+21dB @
Pot center
+1dB @
Pot center
-10 dB @
Pot center
+10 dB @
Pot center
12
Comment
Center vs. Max/Min dependent on
Pot taper.
Center vs. Max/Min dependent on
available Pot tapers.
Adjustment range is restricted and
log taper is implemented by a look-
up table, in order to make this a
usable control.
Adjustment range is defined and log
taper is implemented by a look-up
table, in order to make this a usable
control.
®
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