Meter Switch; Meter Display - Benchmark ADC1 USB Instruction Manual

3) Meter Switch

The Meter Switch selects the scale and mode
of the 9-segment LED Meter Display.
Meter Scale and Peak Hold
Function Selection
Set the Meter Switch to "H" (top) to
•
enable the Peak Hold function and set
the scale to a 1 dB step.
Set the Meter Switch to "1" (center) to
•
disable the Peak Hold function and set
the scale to 1 dB step.
Set the Meter Switch to "6" (down) to
•
disable the Peak Hold function and set
the scale to a 6 dB step.

4) Meter Display

The ADC1 USB is equipped with a multi-
function 9-segment LED meter. The Meter
Switch selects either a 6 dB step or 1 dB step
scale and controls the peak-hold function.
Metering is fully digital and post-conversion
for absolute accuracy. The units are dBFS (dB
below the level of a full-scale sine wave, or
more simply, dB below digital clip).
Time constants are built into the meters so all
transient peaks can be observed easily. If a
transient peak has a duration as short as one
digital sample, an LED will be illuminated and
remain illuminated long enough to be
observed by the human eye.
A peak indication mimics the action of the
needle on a peak-reading analog meter, while
ADC1 USB Instruction Manual – Rev C
the remaining LED's will follow the
instantaneous level of the audio.
The red 0 LED indicates that a full-scale
digital code has been reached and that digital
clipping has occurred. Full-scale events as
short as one digital sample, will light the 0
LED. Short single-sample digital clipping
events are often audible, and all 0 dBFS
events should be avoided.
The ADC1 USB has a very large dynamic
range (especially when operating at 24-bit
output word lengths). It is wise to use some
of this dynamic range to provide more
headroom as insurance against clipping.
Leave some extra headroom between your
highest anticipated peak and the red 0 dBFS
LED.
Input Gain Adjustment
Each channel on the ADC1 USB is equipped
with a 3-position first-stage gain switch. The
first gain-stage provides exceptional noise
performance at gains of 0 dB, +10 dB, or +20
dB. This stage is followed by a second-stage
having a continuously variable gain range of
-5 dB to +19 dB. This gain structure provides
ultra-high performance at any gain setting
between -5 dB and +39 dB. The higher gain
settings will allow direct connections from
many electronic instruments and instruments
with pickups (no DI box required).
At a gain setting of 0 dB, the converter will
reach full-scale (0 dBFS) with a +24 dBu
input level. The calibrated gain trim-pots are
factory calibrated for 0 dB second-stage gain.
Page 9