ALFAtron ALF-DSP88-U, Руководство пользователя, Страница: 24 / 48

ALF-DSP88-U
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3.3.7 Auto Mixer
In a conference room, if several microphones are opened to the same gain level and there is only one person speaking, the
audio pickup of the microphone may be not clear. Other microphones will pick up noise and reverberation in the room.
When these signals are mixed with the desired ‘speech’ signals, audio output quality may be greatly reduced and become
un-intelligible. In addition, the whole audio signal chain may be over energized by excessive gain and could start feeding
back, result in a feedback loop, or ‘ringing’ sound. To solve the issue, other unused microphones should be closed or ‘muted”
when not in use. The auto mixer is used to automatically open and close microphones based on signal input level.
There is a built-in gain share auto mixer inside the processor. It supports up to 8-channels. There is also a direct output at
each channel of the auto mixing matrix, which is only influenced by channel mute and bypasses the auto mixer functions like
auto gain and channel fader. Channels suitable for fixed volume like background music need to be kept at a fixed level
without being controlled by the auto mixer. For example, it will keep a microphone normally open. Its gain will then not be
influenced by the auto mixer. At this point, users may directly adjust the output of the channel in the matrix router as well as
turn off the auto mixer button of the channel. Its gain will not be adjusted and gains at other channels will not be influenced
by the signal level at the channel.
There are two groups of control parameters in the auto mixer module: main control parameters and channel control
parameters.
(1)
Main (Global) control parameters
Click the ON / OFF button to turn the auto mixer on or off.
Gain: Controls the main output volume of the auto mixer
Slope: The slope control influences the attenuation of lower levels. If the slope is high, the
attenuation of lower-level channels will rise. The slope control and the ratio control at the
expander has the same working mode. It is suggested that the value be set at or around 2.0.
If it is set at 1.0, the effect is equal to closing the auto mixer at all channels. If it is set at 3.0,
the action will result in larger gain adjustment, which may bring unnatural volume levels. The
bigger the value, the more the channel is opened and the more the total attenuation. When
the slope is set at 2.0, ideal gain sharing may be realized, so it is the preferred value to use.
Response Time: Faster response time may ensure that the first letters of spoken words are
not cut off. Slower response time allows smoother operation. Practice shows that the best
effect will be produced when response time is between 100ms and 1000ms. The design of
auto gain aims for faster microphones switching. Therefore, first letters of spoken word will
not be cut off even if the response time is set to 100ms. If it is set at several seconds, then
there will be a longer hold time of the response time of the auto mixer, previous active
channels will be saved at open status for several seconds.
(2) Channel control parameters
Auto Mixer: Each channel has an auto mixer on / off button which must be turned
on for that channel to participate in the auto mixer. When in Off mode, that channel
will not participate in the auto mixer.
Mute: Both the channel mute and volume fader are post the auto gain processor. If
the channel level is higher, the level gain of other channels may also be reduced
even if the channel mute is on.
Gain: The Gain fader adjustment may increase / decrease the volume amount of that
channel in the auto mixer.