Solving Audio Problems Using Automatic Mixers

In Uncategorizedby tfwm

As worship facilities have grown larger and sound systems have become more elaborate, the sound engineer’s job – to provide audio that is intelligible, pleasing to listen to, and sufficiently loud – has become much more difficult. This is primarily due to simple acoustics: each microphone added to a sound system picks up background noise and hollowness from the room, and increases the chance of feedback. In other words, the more open microphones you have, the more difficult it is to please the increasingly critical ears of your audience.

Any sound system operator who has tried to chase a dozen faders on a mixer during a holiday pageant has probably thought that there must be a better way. Isn’t there a box that will automatically turn the right microphone up at the right moment, and turn it off when it’s no longer needed? Such a device would reduce the need for constant knob turning, enabling the operator to focus on the quality of the sound rather than the quantity of it.

One solution to these problems is an automatic mixer. Simply put, an automatic (or “voice-activated”) mixer does what a human operator would do: turn up the appropriate microphone in response to sound. When the sound ceases, the microphone is turned down. The way in which the mixer determines when to activate a microphone (and when not to) is critical to ensuring that it will perform well in a modern worship setting.

Early automatic mixers required the user to manually set a turn-on point or “threshold” for each microphone. The microphone would activate only for sounds that were louder than the threshold. If the thresholds were not set perfectly, microphones might not activate for soft talkers, or might turn on in response to unwanted ambient noise such as air conditioning. Of course, this proved to be a problem in worship applications, where the same microphones must accommodate many different talkers under widely varying acoustic conditions. As a result, early automatic mixers often proved to be something less than truly “automatic.”

The latest generation of automatic mixers adapt to changing conditions, eliminating the need for constant adjustments. Because they do not require any special microphones or cabling, today’s automatic mixers are easy to integrate into existing systems, providing an affordable, reliable solution to the audio problems that plague many houses of worship.

To be effective in a worship environment, an automatic mixer must perform certain functions flawlessly. It must instantly sense the onset of speech, and turn the microphone on so fast (preferably just a few milliseconds) that not even a fraction of a syllable is missed. The speech detection circuitry has to constantly adapt to a variety of acoustic conditions: open windows and humming fans in summer; whooshing heater ducts and rumbling furnaces in winter. Somehow, an automatic mixer must be able to sense the difference between such ambient background noises and more dynamic, desired sounds like speech.

Further, the mixer must somehow “know” when the same talker’s voice is being picked up by two microphones – such as when a pastor wearing a wireless lavalier mic walks up to a podium equipped with a gooseneck mic – and automatically select the better signal. If more than one person does speak, the mixer should slightly reduce (attenuate) its master output level to prevent feedback from occurring, just as a human operator would do. This ability is called “NOMA” – Number of Open Microphones Attenuation. The ideal mixer would allow one or more microphones to remain at least partially live when no one was speaking, to prevent annoying “dead air” gaps in recordings or radio broadcasts.

Finally, the mixer should permit the automatic function to be defeated on selected microphone channels. This is necessary in the case of music, for example, where the steady tonal characteristics of musical instruments tend to mimic noise rather than speech, making automatic mixing inappropriate for that part of the audio mix.

Increasingly, small churches that do not have a trained sound system operator rely on an automatic mixer as the core of the system. No one needs to remember to turn the appropriate microphone on or off at different services. As the facility grows and more musical performers are added, the automatic mixer’s role can change to that of a sub-mixer for the speech microphones, with its output connected to an input on a larger mixing console. This arrangement combines the best of both worlds: automatic mixing of speech, and manual mixing of music. The same “sub-mixing” approach allows automatic mixers to be used to expand a sound system to handle additional microphones during special holiday productions. No matter how many extra microphones are added, the operator never has to guess at which actor is wearing which lavalier microphone. The master output of the automatic mixer provides a separate volume control for the actors’ audio, and eliminates the need to disrupt the cabling that is already in place.

The combination of these “intelligent” mixing features defines the modern, user-friendly automatic mixer. All of the following should be present for it to be a truly effective tool:
• Ability to discriminate between speech and ambient noise
• Quick, seamless microphone activation
• Automatically adaptive threshold
• Automatic level adjustment based on the number of active microphones
• Ability to override automatic functions on individual channels as required
• Ability to expand with the needs of the facility

With their superb speech detection and easy setup, today’s automatic mixers are bringing sound quality and system flexibility to new levels in houses of worship. Contact your sound contractor for more information on how automatic mixing can improve the sound in your facility.