Tuesday, June 13, 2006

Gain Structure :|: Corrections and Clarifications

Today's Topic: The Basics

Some things make me feel old. Other than the fact that I am old, some of those things are the birthday that I'm facing this week and the amazing amount of time that's passed since I graduated from college.

Yes, I did graduate from college. Some of you that read my posts on Gain Structure may have been wondering if I even went to middle school. A good friend of mine, who heads up the sound crew here at Covenant Life, pointed out some errors in what I wrote, so I thought I would correct and clarify as appropriate.

From Intro to Gain Structure and Steps of Application

You may have noticed a slight discrepancy between the drawings in Intro to Gain Structure and the actual steps of application that I listed. The discrepancy is that the drawings line up the top of the dynamic range, or the point of distortion, of each piece of equipment. In my application steps, I recommend that you line up the 0dB points of each piece of equipment.

To be sure they are not the same thing, and I was aptly corrected. To maximize dynamic range, one must actually line up the point of distortion of each piece of equipment. The goal is to have each piece of equipment clip at exactly the same time.

However, to find the point of distortion, you must have access to an oscilloscope or some other measurement device that will show you the clipping point at the output of each piece of equipment. I wouldn't recommend trusting the "peak" meters on your equipment to find that point.

Because not everyone has an oscilloscope, I still think it is fair to use the 0dB point to match up your gain structure. It is simpler and it will improve almost any sound system when done correctly. If you are a stickler for perfection and have the equipment, definitely line up your gain structure according to the point of distortion.

From Gain Structure Within Your Mixer

When attempting to show that one should lower levels at all the inputs when using many channels together, I wrote this:
If only 1 channel is turned on, the master outputs are at 0dB. With 2 channels, they hit +6dB. With 4 channels, they charge to +12dB. 8 channels = +18dB; 16 channels = +24dB; 23 channels = +25dB to +26dB.
Please know that this is only true if all of your channels are exactly the same thing, such as a tone or pink noise. It will not add up quite as dramatically in the real world because the different sources are not perfectly coherent like this. However, the general principle is still true.
When combining multiple input channels together within your mixer, reduce the levels at the channel strip, before they add together and are passed on to the master output level.

If I've made further errors, please let me know! I am not perfect. I don't have this all figured out. And sometimes in order to be clear, I'm not quite correct.

Thanks for understanding and for reading nonetheless!

More Posts on the Basics

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