Lectrosonics DC1 - Manual (Page 4)

THEORY OF OPERATION (cont’d)
The DC1 audio signal path is designed to eliminate any signal degradation from the DC1 itself. State of the art
microphone preamplifier and voltage controlled amplifier (VCA) ICs are used to process the audio signals. When
the Bypass mode of operation is selected from the front panel, all VCAs are set to unity gain and microphone signal
pass through unaffected. A hardware bypass capability is provided by relays which switch all three pins of the input
and output XLR connectors. If power to the DC1 is lost for any reason, the relays will automatically drop into the
hardware bypass mode, giving fail safe operation. A setup mode exists on the DC1 where the actual input levels of
the microphones are displayed in real time so that differences in microphone sensitivity may be determined.
The automatic mixing algorithm used by the DC1 is called "Adaptive Proportional Gain" (patent pending). The
channel sense level (consisting of a combination of Pre-VCA and Post-VCA signals) from each channel is
continuously compared to the system sense level (the sum of all channel sense levels). Each channel is then
attenuated based on the difference, in dB, between its sense level and the overall sense level. System gain is
automatically shifted toward the microphone(s) with the greatest signal level. As a result, no "threshold" is
necessary to determine when to turn a channel on or off, and the gain allocation is not affected by changes in
ambient noise in the room.
In addition to preamp gain and phantom power, there are a number of other operational parameters that may be
adjusted on the DC1 to optimize the performance for any application. Each channel has two modes of operation,
Auto and Direct. Auto mode sets the channel for automatic operation. Direct turns the channel on under all
circumstances.
Level Match allows the apparent channel signal level to be increased or decreased by up to 30dB, in 1dB
increments. The actual audio signal path gain is unaffected by changes in the Level Match value. The Level Match
function is used to minimize variations in sensitivity (and as a result, access to the system) which might result from
the use of microphones with different sensitivities in the system. In addition, the Level Match function may be used
to give a soft talker access to the system equivalent to louder talkers.
The off attenuation of each channel is also adjustable, from 6dB to 20dB, using the Max Attenuation function. This
allows inactive channels to be attenuated to a greater or lesser degree, depending on the application.
The Auto Gain Skew function provides the capability to minimize the interruption of the active microphone by non-
speech signals such as coughs, paper rattling, etc. Auto Gain Skew dynamically changes the relative proportion of
Pre-VCA to Post-VCA signals which comprise the sense level for a channel. In this way, channels which are active
for a significant amount of time will tend to dominate inactive microphones. Auto Gain Skew also helps eliminate
"bleed-over" of a talker into adjacent closely spaced microphones.
An AutoSet function is included to simplify the process of setting the important parameters of the DC1. The
AutoSet function allows different types of microphones (typically with different sensitivities) to be used with the DC1.
AutoSet automatically calculates the sensitivity differences in the microphones and sets internal parameters for
optimum operation.
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