Lectrosonics DMTH4, Справочное руководство

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Digital Telephone Hybrid
Rio Rancho, NM
11
Output Processing
Output Source Select
The TEL, CODEC and AUX outputs can each be set to
receive a signal from the pink noise generator, the tone
generator, the expansion outputs or from the master unit
outputs. The
pink noise source can be used for sound
masking during operation, and for equalization during
setup. The
tone generator is used for level adjustments
and signal routing diagnostics. The DTMF generator is
used to create the DTMF tones for initiating calls.
In normal operation the
digital matrix delivers the audio
signals to the outputs, which consist of the final mixes
backpropagated from the master unit in the system
via the Digital Audio Network Interface (DANI), with 12
mixes from the main matrix and 2 mixes from the expan-
sion matrix.
CODEC and AUX Output Channels
These outputs include an attenuator to reduce the out-
put level from line to mic level. The passive attenuator
does not change the signal to noise ratio of the signal,
but simply applies user selectable 20 dB or 40 dB of at-
tenuation to reduce the signal level.
Output Signal Processing Stages
Each output channel provides six filters plus a compres-
sor and limiter to idealize the channel for its function in
the sound system. (See Typical Output Signal Process-
ing Block )
Output Gain and Level Indicator
The output level can be adjusted from - 70 dBu to +20
dBu in 1 dB steps to perfectly match the requirements
of the device being fed by the channel. A bar graph is
provided by the on screen GUI to accurately indicate the
output level as it operates and is adjusted.
Filters
Up to six filters can be implemented at each input and
each output to idealize the signal equalization.
The filter types include:
Low pass
High pass
Band pass
Parametric EQ
Low shelving
High shelving
Filter slopes can be selected with 6 or 12 dB per octave
Butterworth or Bessel parameters. Multiple filters can be
assigned to creater steeper slopes in 6 dB steps.
Output Compressor and Limiter
A versatile compressor and limiter are provided at each
output to control the average level and dynamics of the
audio signal, and restrict the maximum output level to
optimize the channel for its purpose. Compression is of-
ten needed when the channel is feeding a recorder, and
limiting is often used to protect a loudspeaker system
and reduce distortion and amplifier overload.
The compressor implementation is a unique “soft knee”
type based on an RMS level detector controlled by a
single time constant parameter. This is a new design
which responds to varying rates of change in the signal
level by dynamically adjusting the attack and release
times for best performance. Adjustment is simplified by
entering a single value (half of the desired release time).
The attack time is then applied by the DSP to vary with
the signal.
The default value is 100 ms, which sets the release
time at about 200 ms. The attack time is signal con-
trolled and varies from about 2 ms to about 100 ms
as is needed to handle the signal dynamics. See the
following page for a closer look at this unique and very
effective compressor.
Compressor adjustment parameters include:
Threshold
Time Constant
Compression ratio
Makeup gain
Limiter adjustment parameters include:
Threshold
Time Constant
Typical Output Signal Processing Blocks
Activity Indicator
Output Gain
-70 - +20 dB
1 dB steps
Six Filter
Stages
Compressor Limiter
Level Meter
Off, LP, HP, BP,
PEQ, LS, HS
6 or 12 dB/oct.
Butterworth or Bessel
when applicable
Threshold
Comp. Ratio
Time Constant
Indicator
Activity Indicator
Gain Reduction Indicator
Threshold
Time Constant