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343 lines
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<meta name="generator" content="Adobe RoboHelp 9">
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<title>Gated Automixer</title>
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<h1 class="firstHeading">Automixer Gated</h1>
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<p> <img src="gated automixer.jpg" alt="" border="0"></p>
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<h2>Overview</h2>
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<p>The gated automixer is designed to replace a standard mixer and to provide
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a degree of automatic mixing with little or no manual input. All channels
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are gated to remove low level noise. As a signal is detected on a particular
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channel the gate requests to open. However, the gated automixer may or
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may not allow the gate to open based on a number of rules. These rules
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allow the installer to specify a maximum number of open microphones (NOM)
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as well as allocating priority levels to individual channels. The gated
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automixer will manage the channels such that the number of open microphones
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does not exceed the NOM value as well and ensuring the highest priority
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channels take preference over lower priority channels.</p>
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<h4>Priority Scheme</h4>
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<p>Each channel of the gated automixer is allocated a priority between
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1 and 32 (1 is the highest priority). As the channel gates try to open,
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their priorities are compared and only the highest priority channels are
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allowed to open. This means that higher priority channels will take preference
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over lower priority channels. In some cases this may mean that an existing
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channel will be muted because a higher priority channel has opened.</p>
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<h4>NOM</h4>
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<p>This parameter limits the maximum Number of Open Microphones (NOM) allowed
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in the system.  Numerous open microphones present in the system will
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cause the ambient noise of the system to increase as well as causing potential
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audio coupling (feedback or howling) between the open microphones and
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the system speakers.  The gated automixer keeps the ambient noise
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to a minimum and prevents acoustic feedback by automatically reducing
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the gain of the system.  The amount of attenuation applied is determined
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by the number of open mics.</p>
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<h4>NOM Attenuation</h4>
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<p>For every doubling of open channels (mics), the gated automixer will
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reduce the gain by the amount of the NOM Attenuation parameter.</p>
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<h4>Duck Gain</h4>
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<p>Some applications require that higher priority channels not only take
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preference when deciding which channels should be open, but also that
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they should be louder than lower priority channels. The duck gain allows
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you to specify how much a lower priority channel should be ducked by if
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a higher priority channel is open.</p>
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<h4>Default Mic and Last Mic</h4>
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<p>In some circumstances the installer would want to allocate one microphone
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as the <20>default<6C>. If all channels are below threshold then the default
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microphone channel will open automatically.</p>
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<p>If no default is set then the Last Mic setting can be used to leave
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the last microphone on even though it has dropped below the threshold.</p>
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<h4>Adaptive Threshold</h4>
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<p>The level at which a gate opens is the channel threshold, however, in
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some circumstances having a fixed threshold can be problematic. For example,
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if an audience applauds loudly this may raise the level above the threshold
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on many channels causing the gated automixer to open those channels in
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error. To implement an adaptive threshold the <20>Threshold In<49> input is
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typically connected to an ambient microphone. As the ambient level rises
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then the gate thresholds also rise so that they are less likely to open.</p>
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<h4>Cascaded Automixers</h4>
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<p>The gated automixer is capable of being cascaded to create much larger
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gated automixers. The gated automixers must be connected via BLU Link
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because of the digital nature of the information being passed between
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them. They cannot be connected via analog cards, digital cards or <a href="Cobranet Information.html">CobraNet</a>.
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A number of cascaded gated automixers act as a single very large gated
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automixer up to thousands of channels.</p>
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<h2>Internals</h2>
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<p>The internal audio processing for a single channel of the gated automixer
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is shown below :-</p>
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<p style="text-align: center;"><img src="mixer_internals.jpg" alt="" border="0"></p>
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;
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<ul type="disc">
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<li class="p"><p>The input audio first passes through the channel gain
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before being fed into both the Gate Threshold Detect and the Gate
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Attenuation.</p></li>
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<li class="p"><p>The Gate Threshold Detect monitors the audio level
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to decide if the gate needs to open taking into account the current
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level of the ambient input.</p></li>
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<li class="p"><p>The output of the Gate Threshold Detect passes through
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the Priority Logic which decides if the channel may actually open
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and also the level of NOM attenuation and duck gain that should be
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applied. All channels feed into the same Priority Logic so it can
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decide which channels should come on based on their priorities and
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the NOM etc.</p></li>
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<li class="p"><p>The Priority logic then sends control signals to the
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Gate Attenuation (to open or close the gate) and also to the NOM Attenuation
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(to apply the NOM attenuation and duck gain).</p></li>
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<li class="p"><p>The resulting signal is then mixed with all the other
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channel outputs to create the output signal. If direct outputs are
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enabled they are taken before the mixer.</p></li>
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<li class="p"><p>In the case of a cascaded automixer the Priority Logic
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communicates with the logic in the other automixers via the chain
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signals to ensure that they all act as a single large automixer.</p></li>
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</ul>
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<p class="hcp1"><span class="hcp2">Note</span>:
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- The NOM attenuation and duck attenuation are applied even when the gate
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is closed and therefore the signal will be attenuated by the off gain
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plus the nom attenuation and the duck gain. The reason for doing this
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is to ensure that when the gate opens the channel is already at the correct
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level. Also, if the NOM and duck gain were not applied to the <20>off<66> signal
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then it would be possible for the <20>on<6F> signal to actually be quieter than
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the <20>off<66> signal.</p>
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<h2>Inputs and Outputs</h2>
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<ul type="disc">
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<li class="p"><p class="hcp3">The number of inputs can
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be set from 2 to 96.</p></li>
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<li class="p"><p class="hcp3">The output can be either
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mono or stereo.</p></li>
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<li class="p"><p class="hcp3">The direct out property
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produces an output per channel.</p></li>
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<li class="p"><p class="hcp3">The master option adds
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a further Mix Input, Chain Input and Chain Output.</p></li>
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<li class="p"><p class="hcp3">The slave option adds
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a further Mix Input, Chain Input, and Chain Output.</p></li>
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</ul>
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<h2>Properties</h2>
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<h4>Number of Channels:</h4>
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<p class="hcp3">The number of input channels can be selected
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between 2 and 96.</p>
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<h4>Stereo:</h4>
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<p class="hcp3">Set to "Yes" the gated automixer
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will have a stereo pair of outputs, L and R. In Master or Slave mode there
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will also be a Left and Right Mix Input</p>
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<h4>Pan Law:</h4>
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<p class="hcp3">The law of the pan controls may be set to
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either -3.0dB, -4.5dB or -6.0dB. These figures relate to the attenuation
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applied to each channel at the central pan position.</p>
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<h4>Master/Slave Status:</h4>
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<p class="hcp3">For expanding the mixer, either for making
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a larger mixer within a device, or for splitting a mixer across more than
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one device. The control signals are shared using two special versions
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of the gated automixer <20> Master and Slave.</p>
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<h4>Voice Band filters:</h4>
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<p class="hcp3">Filtering may be included so that the automixing
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action favours frequencies in the human vocal range. This helps the mixer
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to distinguish between speech and noise, giving a voice signal a better
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chance of 'winning' against a noise signal on another channel.</p>
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<h4>Direct Outs:</h4>
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<p class="hcp3">In addition to a single mixed output, the
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individual channels may be output for further processing or mixing elsewhere.
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These individual outputs are taken from before the mix but after any processing
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such as priority logic, gain and so on are applied.  Set to Yes if
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Direct outputs are required.</p>
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<p style="font-style: normal; font-weight: bold;">Channel Number Start:</p>
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<p class="hcp1"><span style="font-style: normal;">Only available
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for the slave option.  Since the slave automixer is cascaded from
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a master it is likely that you would want the channel numbering to continue
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from the last channel number of the previous automixer.</span>  </p>
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<h2>Control Panel</h2>
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<p><img src="GA_panel.jpg" alt="" width="699" height="661" border="0" class="hcp4"></p>
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<h4 class="hcp5">Channel Controls</h4>
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<p><span class="hcp2">Polarity</span> button for each input
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for signal inversion.</p>
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<p><span class="hcp2"><a name="Local_Gate_button_for_each_input._If_set_the_attack,_hold_and_release_settings_for_the_gate_are_specified_in_the_channel_strip_rather_than_in_the_Global_Gate_section."></a>Local
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Gate</span> button for each input. If set the attack, hold and release
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settings for the gate are specified in the channel strip rather than in
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the <a href="Gated_Automixer.htm#Global_Gate_Controls">Global Gate</a> section.</p>
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<p><span class="hcp2"><span class="hcp2">A</span>ttack</span>
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control sets the gate attack time for the channel. Only available if the
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Local Gate button is on.</p>
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<p><span class="hcp2">Hold</span> control sets the gate hold
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time for the channel. Only available if the Local Gate button is on.</p>
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<p><span class="hcp2"><span><span><span class="hcp2">R</span></span></span>elease</span>
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control sets the gate release time for the channel. Only available if
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the Local Gate button is on.</p>
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<p class="hcp6">Threshold <span class="hcp7">control
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sets the gate threshold for the channel. This is the level at which the
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gate opens. The gate threshold may be raised due to the  <a href="Gated_Automixer.htm#Ambient_Controls">Adaptive
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Threshold</a>.</span></p>
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<p><span class="hcp2">Off Gain</span> control for each input:
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Determines what maximum attenuation will be applied to the channel when
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off.</p>
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<p><span class="hcp2">Gate Override</span> button for each
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input: Force the gate to open for that channel. The channel is still subjected
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to priority logic so may still be muted.</p>
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<p><span class="hcp2">Gate indicator</span> for each input
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shows when a channel is above threshold (the gate wants to open).</p>
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<p class="hcp6">Open indicator <span class="hcp7">for
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each input shows when a channel is active.</span></p>
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<p><span class="hcp2"><span class="hcp2">P</span>an</span>
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control (stereo objects only)</p>
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<p><span class="hcp2">Gain fader</span> for each input. This
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controls the level of the channel's input before the automix logic is
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applied.</p>
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<p><span class="hcp2">Mute</span> button for each input.</p>
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<p><span class="hcp2">Solo</span> control for each input
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channel for quick identification of signals and level setting: Allows
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only 'soloed' channels to be heard.  Note the NOM count is invalid
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when any channel is solo'ed.</p>
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<p class="hcp6">! <span class="hcp7">This
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is a 'solo-in-place' which impacts the main output.</span></p>
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<p class="hcp6">Default Mic<span class="hcp7">.
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One microphone can be set to be on as the default when all channels are
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below the threshold.</span></p>
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<p><span class="hcp2">Priority</span> control for each channel.
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1 is the highest priority and 32 is the lowest.</p>
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<p><span class="hcp2">Auto</span> <span class="hcp2">button</span>
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assigns each channel to operate as either a conventional mixer channel
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or an automated channel. By switching Auto to off the channel is completely
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removed from the automix logic and NOM attenuation.</p>
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<p><span class="hcp2">Signal Name</span> shows the name of
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the input signal</p>
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<h4 class="hcp5"><a name="Global_Gate_Controls" id="Global_Gate_Controls"></a>Global
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Gate Controls</h4>
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<p><span class="hcp2">Attack</span> control sets the gate
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attack time for all channel gates with the exception of any channels which
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have the <a href="Gated_Automixer.htm#Local_Gate_button_for_each_input._If_set_the_attack,_hold_and_release_settings_for_the_gate_are_specified_in_the_channel_strip_rather_than_in_the_Global_Gate_section.">Local
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Gate</a> button set.</p>
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<p><span class="hcp2">Hold</span> control sets the gate hold
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time for all channel gates with the exception of any channels which have
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the <a href="Gated_Automixer.htm#Local_Gate_button_for_each_input._If_set_the_attack,_hold_and_release_settings_for_the_gate_are_specified_in_the_channel_strip_rather_than_in_the_Global_Gate_section.">Local
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Gate</a> button set.</p>
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<p><span class="hcp2">Release</span> control sets the gate
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release time for all channel gates with the exception of any channels
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which have the <a href="Gated_Automixer.htm#Local_Gate_button_for_each_input._If_set_the_attack,_hold_and_release_settings_for_the_gate_are_specified_in_the_channel_strip_rather_than_in_the_Global_Gate_section.">Local
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Gate</a> button set.</p>
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<p><span class="hcp2">Hysteresis</span> control sets the
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level below threshold that the gate uses when turning off.</p>
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<p class="hcp8"><a name="Ambient_Controls"
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id="Ambient_Controls"></a>Ambient
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Controls</p>
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<p><span class="hcp2">Threshold</span> control set the ambient
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level at which the adaptive threshold starts. Above this level the gate
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thresholds will be raised accordingly.</p>
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<p><span class="hcp2">Attack</span> control sets the speed
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at which the adaptive threshold logic responds to changes in the ambient
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level.</p>
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<p><span class="hcp2">Release</span> control sets the speed
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at which the adaptive threshold logic responds to changes in the ambient
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level.</p>
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<p><span class="hcp2">Ambient meter</span> shows the current
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ambient level.</p>
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<p class="hcp8">NOM Controls</p>
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<p><span class="hcp2">NOM</span> control sets the maximum
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number of open microphones while NOM count displays the number of microphones
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which are actually open.</p>
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<p><span class="hcp2">Attenuation</span> control sets the
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amount that the output gain is attenuated by per doubling of open channels.
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For example, if the attenuation is -3dB and the number of open mics is
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2 then -3dB of gain will be applied to the output. If the number of open
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channels is 4 then -6dB of gain will be applied.</p>
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<p><span class="hcp2">Speed</span> control sets the speed
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at which the NOM attenuation is applied.</p>
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<p><span class="hcp2">Last Mic</span> control tells the automixer
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to leave the last open mic on even if the level drops below the gate threshold.</p>
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<p><span class="hcp2">Duck Gain</span> control sets the amount
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that lower priority channels are attenuated by if a higher priority channel
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is also open.</p>
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<p><span class="hcp2">Nom Attenuation meter</span> shows
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the current NOM attenuation that is being applied.</p>
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<p class="hcp8">Master Mix Controls</p>
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<p><span class="hcp2">Master Gain</span> control for the
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Main output(s)</p>
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<p><span class="hcp2">Master Mute</span> button for the Main
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output(s)</p>
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<h2>Automixer Expansion</h2>
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<p>It is possible to combine several gated automixers together so that
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they act as one very large gated automixer. This makes use of the Master/Slave
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Status setting in the Properties Pane and also makes use of the Chain
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control signals. If the automixers are on different devices then the Chain
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control signals can only be sent over <a href="BLU_link.html">BLU Link</a>.
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The gated automixers are always connected in a ring with a single master
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and one or more slaves.</p>
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<h4>Connecting two Gated Automixers</h4>
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<p>Connect the Chain Out of the master to the Chain In of the slave, and
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the Chain Out of the slave to the Chain In of the master. If you require
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the outputs of the two mixers to be combined, connect the Mix Out of the
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slave to the Mix In of the master, then use the Mix Out of the master.</p>
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<p> <img src="2GA_1.jpg" alt="" width="319" height="271" border="0" class="hcp4"><img src="2GA_2.jpg" alt="" width="404" height="269" border="0" class="hcp4"></p>
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<h4>Connecting more than two Automixers</h4>
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<p>Create one master and several slaves and connect the Chain Out of the
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master to the Chain In of the first slave. Then <20>daisy chain<69> the Chain
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Out of the slave to the Chain In of the next slave, and so on (in any
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order) to the Chain In of the master. If you require the outputs of all
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the mixers to be combined, 'daisy chain' the Mix Out of one slave to the
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Mix In of the next slave and so on (in any order) to the Mix In of the
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master, then use the Mix Out of the master.</p>
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<p><img src="many_GA_1.jpg" alt="" width="314" height="541" border="0" class="hcp4">               <img src="many_GA_2.jpg" alt="" width="407" height="541" border="0" class="hcp4"></p>
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<h2>Notes on connecting several Gated Automixers</h2>
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<ul type="disc">
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<li class="p"><p>The Speed controls should be set the same on all linked
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gated automixers for consistent operation.</p></li>
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<li class="p"><p>The Chain signals can only be sent via <a href="BLU_link.html">BLU
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Link</a> if the automixers are on different devices. Those signals
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are digital information and rely on the bandwidth and low latency
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of BLU Link for correct operation. They cannot be sent by any other
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means. They are displayed using a different line color in London Architect
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to help differentiate them from audio signals.</p></li>
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<li class="p"><p>If you are using adaptive threshold then the ambient
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signal must be connected to the Threshold In of all gated automixers
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manually.</p></li>
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<li class="p"><p>When connecting several automixers together the data
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takes longer to circulate around the loop. The time it takes for the
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data to circulate around the loop has an effect on the attack time
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of the gates. The BLU Link network is low latency so under normal
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circumstances the round trip time is very short and does not adversely
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affect the gate attack time. However, in some very large BLU Link
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rings with many slave gated automixers the round trip may become significant.
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Switching the design to 96KHz will halve any communication delays
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since the devices and the BLU Link network all run at double the speed.</p></li>
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<li class="p"><p>When gated automixers are cascaded across 2 or more
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devices you may require an indication that they are connected.  For
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this purpose an LED is available for use on custom control panels.
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 You can access this from the <a href="MAINDesign_tree.htm">design
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tree</a> in the NOM folder for the gated automixer in each device.
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 Just drag and drop onto the custom panel.  If for any reason
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the link between automixers is broken (e.g. Blu link is pulled out)
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the LED on your custom panel will go off.  In the event of a
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broken link, the slaves mute and the master reverts to fully functional
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standalone. When the link is re-established, cascaded functionality
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resumes (including any changes made to the masterslave(s) during broken
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link). Whenever the link is established or broken an event is logged
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in the <a href="MAINEvent_Log.htm">eventlog</a> and the LED set accordingly.</p></li>
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</ul>
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<h2>Generating the ambient from mics</h2>
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<p><img src="image11.jpg" alt="" width="703" height="177" border="0" class="hcp4"></p>
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<p>Sometimes it is not convenient to install a dedicated ambient microphone
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and in those situations the signals from all the microphones can be summed
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using a mixer to produce the ambient signal.</p>
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<p class="hcp1"><span class="hcp2">Note: !</span>
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This object is capable of raising signal levels beyond the clipping point,
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so care should be exercised when using positive gain values.</p>
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</body>
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</html>
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