Intelligibility by Design

Intelligibility Newsletter April 2011

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The audiovisual industry is facing an exciting phase with new technological developments driving and raising applications to new heights. We at Audio Systems Group consider ourselves fortunate to be moving on to our 21st year in the business as the industry leaps forward, opening new opportunities.

We are pleased to share our first hand experience with you and bring you the inaugural issue of Intelligibility, a special 14-series monthly newsletter designed to offer expert advice for increasing professionalism and effectiveness on the job. This special series will guide you through the most important issues in sound reinforcement, disclosing crucial intelligibility punch lists for novice and experienced technicians alike.

Audio Systems Group has the experience of creating a line of over 170 audiovisual solutions including electronics, cables, microphones, speakers, and stands and we will continue to develop valuable industry contributions such as the Quarterack and the Summit Lectern. Our philosophy, at Audio Systems Group, is to provide correct and effective solutions to real problems encountered by AV professionals. Our high quality products are backed by our genuine desire to help improve the quality of work that you do.

We hope this issue of Intelligibility will help make you better AV Professionals because at Audio Systems Group, we believe that the achievement of our goals is best measured by your success.

Welcome Note

The purpose of these articles is to help both the new and the seasoned AV technician. Much of what I will cover you may already intuitively understand, but it is good to review the importance of these issues. This is all for the common good, so if I mess up or if you have something to add, please let us know via e-mail.

For the first installment of the Intelligibility newsletter, I thought I would cover the easiest-to-fix and the most common intelligibility buster used: the equalizer knobs on the mixer. Misuse of the equalizer on the mixer will not typically destroy intelligibility by itself, but it will at least take the edge off. Time and time again, when working freelance I see the sound techs do what I used to do --- boost the bass and treble and cut the mid range EQ. The funny thing is that is the opposite of what should be done for voice communication. The reason this happens is because technicians are used to producing music, and it makes the person talking on the microphone sound bigger than life. Where this MIGHT be somewhat appropriate for music; as a musician, composer and music listener, I prefer to be able to understand the words to a song and I enjoy hearing a singer with unique timbre and resonance.

Let us discuss each knob independently. First of all, the low-frequency knob; any sound below 80 Hz is not in the vocal range and will interfere with intelligibility. The guide here is to attenuate the low frequencies as much as possible without making the voice sound too thin and unnatural. Adding bass makes the speaker's voice sound more rich, but why not have the speaker sound natural and be able to understand what he is saying?

Why is adding bass bad? Adding bass takes away from the headroom of the amplifier and speakers, adding distortion. Distortion is an intelligibility buster, and the extra low frequency bouncing around the room muddles up the speaker's voice, making it difficult to understand. Attenuating bass provides more headroom for all of the components of the sound system and reduces distortion.

The mid-frequency knob is the one that should be boosted. Consonances are the key to intelligibility, and consonances are in the mid frequency range. Boosting the mid-frequencies a little provides an edge to intelligibility, helping everyone understand what is being said. I know sign language and used to work with the hard of hearing; attenuating the mid frequencies is like making everyone in the audience hard of hearing. They will be able to hear the sound system, but without the mid frequencies they will either not be able to understand what is said, or will have to strain to listen in a way that they can understand, causing fatigue.

The reason to attenuate the high frequency is to avoid too much sibilance. Too much sss in the letter s is distracting at least. Mouth noises are also distracting. At the normal listening distance of two people talking, the mouth noises fade and get filtered out; we are not used to hearing them.

Setting the EQ on the board is the simplest thing to do to either degrade or improve intelligibility. Generally, for a place to start, I attenuate the bass to about 10 o’clock, boost the midrange to about 1 to 2 o’clock and cut the highs to about 11 o’clock. As with this whole subject, things are relevant to the system, the program, and the acoustics of the room. The tenant here is to set the EQ so that the human voice sounds natural with just a little boost in the midrange, to insure that everyone can hear, and understand.

Intelligibility