Audio SigGen

AMM

The Automatic Mic Mixer (AMM) provides automatic level control of multiple microphones for spoken word applications such as conferences and discussion panels involving several participants each with their own mic around a table . This improves intelligibility and can reduce the risk of feedback by reducing the levels of mics which are not being spoken into. Once set, the AMM needs little or no change at all whilst still allowing the engineer to maintain absolute control of the mix.

Note The AMM is intended for speech applications not music.

Operating Principles

The AMM takes control by first setting each assigned channel fader to '0' (0dB unity gain), thus effectively passing the signal unaffected through the fader, and then using its own post-fade gain element to make its automatic adjustments.

The AMM affects all channel post-fade sends but not pre-fade sends such as monitors.

The AMM determines when microphones are open (detects a level or speech) by analysing the channel signals at their pre-Insert point. The position of the channel fader will affect the signal detection when the AMM has Follow Fader enabled, otherwise the fader position will not influence the signal detection. The PEQ and Comp do not affect AMM signal detection.

Enabling mute on a channel will mute the signal to the AMM and to any mixes that the channel is routed to.

The AMM uses a complex algorithm to automatically optimise the overall gain by adjusting the microphone levels sent to the mix according to how many mics are open.

If just one mic is open then its level is passed through at 0dB and the others are attenuated. If several mics are open the overall gain is automatically reduced.

Additional features allow ambience to be maintained, crosstalk and false triggers to be eliminated, and microphones to be selected as 'Chair' to take priority over others by ducking their levels.

The AMM is assigned and set up using the Setup / Audio / AMM screen. This displays the current mode and assignments as well as blue bars showing the automatic gain settings.

Once channels are assigned, the screen lower right toolbar presents an AMM button to give you quick access to the AMM page from any other screen. Touch the button to open the page.

A global IN/OUT switch is positioned at the top of the AMM window which can be used to turn the AMM unit on or off.

Follow Fader can be turned ON or OFF on the Setup page.
When turned ON the position of the fader influences the AMM signal detection.
When turned OFF the position of the fader does not affect the AMM signal detection.

You can choose one of two operating modes using the Setup page:

NOM Mode

NOM (Number of Open Mics) mode evolved from the AMM developed for the Allen & Heath IDR8 installed sound processor, NOM mode acts as a gate, turning an input on when a threshold is passed. The level adjustment for each open input is equal and depends on the number of microphones open and the NOM attenuation parameter which sets the amount of attenuation applied for every doubling of open microphones.

Features:

Adaptive Threshold - You do not need to set the open mic threshold. NOM mode senses the background ambient noise level and automatically adjusts the open threshold level to ensure consistent triggering regardless of background noise.

Ambience Maintenance - Keeps the last open microphone locked on until another channel is opened to ensure consistent ambient noise is maintained, especially important in a broadcast environment. If just one microphone is active in the AMM then it is held open to maintain ambience.

ON - Any combination of mono channels 1-44 can be assigned to the AMM. Stereo channels cannot be assigned to the AMM. When switched to 'ON' the AMM sets the channel fader to '0' and then takes automatic control using its own gain element just after each fader.

Chair Priority - You can set a channel as 'Chair' to give it higher priority over the other channels, for example to let a chairman override another speaker. The Chair mic sensitivity and the amount that other channels are automatically ducked when the Chair is open can be set.

Best Mic On - This option ensures a single participant activates the one microphone receiving the strongest signal. This can prevent crosstalk, phasing and ambience issues caused by multiple microphones triggering for the same voice.

Note We recommend you only select Best Mic On if all microphones involved are the same type and have similar positioning and gain.

Note The Chair mic is not part of the Best Mic On calculation.

Solo - Each input has a solo option which opens the selected channel and turns all others down. This is not additive. Only one channel can be soloed at a time.

NOM Setup:

Side Chain Filter - Set High Pass and Low Pass filters to cut off frequencies below and above the normal speech range that may cause false triggering of the mics.

Off Attenuation - Set the amount of shutoff for closed mics (from -10dB to fully off).

On Hold Time - Set the amount of time an open mic is held open once the trigger is removed (from 100ms to 5 seconds).

Note The Chair mic is not affected by Hold Time.

NOM Attenuation - Set the amount of attenuation applied per doubling of open mics (from 3 to 6dB).

Chair Sensitivity - Set the sensitivity of signal required to trigger a Chair mic open and therefore duck the other mics (from 1 to 10 = least to most sensitive).

Chair Duck Level - Set the amount of attenuation applied to other mics when a Chair mic is open (from -3 to -40dB).

D-Classic Mode

Unlike NOM mode which uses gating and fixed gain attenuation, D-Classic uses a 'constant gain sharing' algorithm to dynamically adjust the gain for each mic proportional to its input level. Louder signals will receive more gain in the mix.

Features:

Priority Level - For each channel you can set a priority 'level' which will offset the amount of gain going into the mix calculation and therefore give a higher or lower artificial gain to that channel. This is a variable slider with a range from -15dB (low priority) through 0dB (no offset) in the middle to +15dB (high priority) at the top.

D-Classic Setup:

Side Chain Filter - Set High Pass and Low Pass filters to cut off frequencies below and above the normal speech range that may cause false triggering of the mics.

D-Classic does not provide Best Mic On, Solo, Chair or other setup functions.

Scenes and the AMM

AMM settings are stored in GLD Scenes. However, these can be made globally safe from Scene recall using the Scenes / Scene Safes screen 'Others' tab. They can also be filtered out of individual Scene recall by highlighting a Scene in the list, touching its Recall Filter button to access its filter 'Others' tab and blocking the AMM item.

User Permissions and the AMM

AMM settings can be protected from selected users by disabling the 'AMM' item in the Setup / Config User Profiles screen Permissions page Setup tab.

Using the AMM

Set up and position the microphones. It is best to use the same type of microphone and position them so that the participants are not too close or too far from each. To avoid false triggering and phasing the distance from each voice to its mic should be closer than the distance between the mics. The distances from each mic to voice should be similar for consistent operation.

Set up an Audio or DCA Group for master control. Decide which mic channels to use for the AMM. Before assigning to the AMM we recommend you either route these via an audio Group to the LR mix (remember to also unassign these channels from the LR mix), or assign a DCA Group to them. This gives you a master fader and mute for quick overall control.

Set the mic gain and processing. It is best to start with the Group master fader down to avoid unexpected high levels in the PA while setting the gains. Use PAFL to check audio level and quality. Set gain for the loudest speech expected. Use the HPF and PEQ to tailor the sound for speech.

Set up the AMM. Use the Setup / Audio / AMM screen. This displays the current mode and assignments as well as blue bars showing the automatic gain settings. Touch the Setup button to choose NOM or D-Classic mode and adjust the available settings.

Assign the channels to the AMM. When you turn an assignment ON its fader will automatically move to its '0' position. The AMM takes over and keeps the mic closed until it picks up enough signal to trigger it.

Bring up the AMM in the mix. Turn one mic on by having someone talk into it. Raise the Group fader to set the required volume in the room.