Music, Sound, and Audio Technology

Bryant Falk has been a producer and engineer for over 12 years working with such clients as �The Ricki Lake Show,� Coca-Cola, Sports Illustrated, Valley National Bank, and MTV�s �The Shop.� His company Abacus Audio handles many aspects of the audio production field from creative and production to mixing and final output. http://www.abacusaudio.com/

�Hey, stop shouting, I heard you the first time!� � �What? What did you say? Speak up!�

The above lines are what I call the extremes of gain. Getting the right level, when recording and mixing, is one of the most important aspects of your audio. Nothing is worse than your audience loosing interest because they can�t hear the dialogue. Or your location audio being completely ruined because the level was too loud and distorted onto tape.

The first question is: what is volume or loudness, anyway? Keeping things simple, let�s call �volume� the quantity of air that is pushed and pulled to and from your ear. In more clinical spaces, we call it compression and rarefaction.

An easy way to look at sound and air pressure is to throw a small ball into a calm pool and watch the little waves or ripples that emanate from the impact. Now find a big bowling ball and throw that into pool in the same manner. Notice how much bigger the ripples are? The bowling ball displaces a lot more water! You have just witnessed a very simple version of volume. If both of the balls were thrown in the same exact manner from the same height, the ripples should be the same distance apart (frequency), but the size of the ripples is very different (volume or loudness).

Keeping with the above metaphor, maintaining a nice looking wave in our pool is like keeping our audio from not distorting to tape. Just like the waves breaking over the edge of the pool (distortion), our audio will break up at the limit of saturation (ability of the tape to record the loudness).

Now an obvious fix is to turn down the volume! But then, there is another problem: the quiet parts are too� quiet.

�So, you�re telling me I need to have someone ride the volume level during the entire shoot and adjust accordingly?� one might ask.

Well, in the old days, that was exactly what had to happen. But now, we have a few more tools that help us control the level of our audio without absolute constant monitoring. One tool is called a �compressor,� and its job is to try and control that gain without a major alteration to the signal. Don�t get me wrong, a compressor can severely change the shape of a signal if used incorrectly!

If you�ve ever looked at a compressor, you will notice at least three main controls, (this can be more or less depending on the amount of parameter control your compressor gives you). Threshold, Ratio and Gain. The first two are the ones that instruct the compressor what to do and when. Threshold is the point at which you want the compressor to act. The Ratio is how much you want the compressor to act at that threshold. So, if you set the threshold at -5db for example, (db or decibels is a logarithmic scale and is a way to measure volume just like miles measures distance; as a reference, every 10 decibels is a doubling of perceived volume), and set the ratio at 4.00:1, then you are telling the compressor to allow only 1db of audio through for every 4db that pass the threshold, (that would be 5db). So, effectively we are controlling our volume level but still allowing the signal to not loose its identity completely.

Now the third parameter, �gain,� is simply the ability to make louder or lower the overall signal coming out of your compressor. It�s common to raise your overall level a touch now that you have gotten the volume under control.

The above description by no means covers the entire function and form of compression, but I hope it provides your first basic understanding of the principle.

The next tool is one you may be more familiar with. It is called a �limiter.� In its raw form, it by no means is as graceful as a compressor, but it does have its uses.

Overloading an audio signal in today�s digital age is a nasty experience. It�s one we all really try to avoid at all cost. Easier for a mixer to gain up a signal and take out some low level noise than try and re-construct a distorted section of audio.

A limiter is like a ceiling that audio levels are not allowed to go past. A lot of audio engineers call it a brick wall. A good place to set a limiter would be a touch below where your recording deck distorts to allow a safety margin for when the limiter kicks in.

Limiters have gotten much more sophisticated in their ability to keep a signal under control. There are companies that make plugins that do an excellent job of controlling level. On most cameras a much more basic limiter is available. Be careful! These limiters may do more damage to your signal than good! Make sure to check your limiters performance before using it to print all your audio files to tape! Most limiters also have a threshold to set when you want the limiter to kick in. They also will have some gain control to adjust output volume. On board (in camera) limiters are, to use the pun, limited. They usually have two options, on and off. This is why you must be careful!

Some new limiters have a �Look Forward� function where the limiter is actually looking at what is coming down the audio pike and making decisions on the best way to handle the impending peak audio. Many times compressors and limiters work hand in hand to control signal level; the compressor doing a smooth job and the limiter as the safety net for any peaks that get through. This is why you will see many external boxes that have both a compressor and limiter on board. With both options in place, you can really control the level of audio printing to your tape and defend against overload.

A great example is when you�re taping a sports game like baseball. For the longest time everything is pretty calm, but then, wham! Someone hits a homerun, and the announcer is off his feet yelling his lungs out! Then it all settles down and happens again an inning or two later.

The above are a slight taste of what these tools can do, and all the many permutations they come in. Take caution and make sure to really check your settings, and if in doubt, play it lighter on the compression with a limiter catching anything that may slip through. Too much compressing can cause what we call a �breathing� sound in your audio as the compressor kicks in and let�s go. Good recording, and good luck!

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Check out this article in the November 2006 print edition of StudentFilmmakers magazine, page 48.