USL CM-8E - Manual (Page 23)

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channel is biamped, two sets of boxes appear above each button. The left one represents the
low frequency band, and the right one indicates the high frequency band.
While one channel is being driven and is selected, click the increase or decrease words above
the proc and amp buttons. This will increase or decrease the height of the VU indicator on the
front of the CM-8E and on the bar immediately above the proc and amp buttons on the web
page.
Note that the CM-8E uses an averaging circuit instead of an adding circuit to combine audio for
the speaker, stream, and front panel VU. Consider what happens in an auditorium if a second
channel is brought up with audio identical to the first. Since there are now two amplifiers
driving the auditorium with the same sound, the power has doubled, indicating an increase of
3dB. If a voltage adder (or summer) were used in the CM-8E, adding two identical voltages
would result in a doubling of the voltage, or an increase of 6dB. As more channels are added,
the sound in the auditorium increases by 3dB each time the number of channels is doubled,
while the output of a summer would increase by 6dB each time the number of channels was
doubled. This could easily result in an overload and clipping within the CM-8E.
With an averaging circuit, the voltages are averaged instead of summed. Averaging the voltage
of two channels with identical audio results in the same audio level no matter how many
identical channels are averaged. In this case, doubling the number of channels results in an
increase of 0dB. If, however, we average a channel and silent channels, the resulting level
drops. If there is audio on only one channel, but we select a second silent channel, the average
drops to ½ the previous value (a drop of 6dB). In the auditorium, of course, adding additional
silent channels results in a sound level change of 0dB. As such, the front panel VU indicator
should be considered accurate only when a particular channel is being monitored and not
when multiple channels are being listened to.
When all the bar graphs are calibrated, press the “Save Settings” button to save the bar graph
calibration.
6.7 Power Up Configuration
The “Save Settings” buttons on the various configuration screens save all the current settings.
The currently selected audio channels/bands for monitoring and the processor/amp selection
are also saved. Use the buttons on the unit or the web page to select which channels are fed to
the speaker and stream, then hit “Save Settings.” These button settings will be restored the
next time the unit is powered up.
6.8 Firmware Update
The CM-8E contains two microcontrollers, identified as P32 and P24. As improvements are
made to the CM-8E, firmware updates will be available on the USL web site.