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Building Blocks 23: Mic Technique 6

Mic Technique pt 6: Gain, Levels, and Feedback

If you open the options panel in DDO and go to audio you will see a section for settings for voice chat.  One of these settings is voice gain, it’s a slider bar.  While it can refer to many things, gain is usually shorthand for transmission gain which is the power increase of a signal.  In very simple terms, gain is input level.  It adjust the volume to an appropriate level for the piece of gear receiving the signal to properly process it.  For a sound board, effects processor, or compressor and similar gear, this brings the audio signal up to a level that allows these pieces of gear to process the signal well.  In the case of DDO, they aren’t doing much more than transmitting your audio signal.  Gain can be set at a value between 0 and 100.  It is important to note that this is an arbitrary value.  While they are relative, these values have no outside meaning.

We want to set gain at what we call a “nominal” level.  This simply means we want a level that is at a setting that is neither too loud nor too soft but rather one that is consistently within the two – a normal level if you will.  To set our level check the “mic test” box.  This will pop up what we call a meter and it will allow you to hear what your mic is picking up.  This pop up meter is very standard to the business of sound and you’ve probably seen such indicators before on other gear.  As you test your mic you will see the meter move correlating to how loud your voice is.  At a certain gain the green meter will turn yellow and a little more gain will turn the meter red.  If your meter is hitting red, you need to turn your gain down because this means you are overloading the system.  This is called clipping, it means that the amount of power behind the audio signal is greater than the system can translate.  The resulting sound will be crackly and distorted.

The thing to keep in mind here is dynamic range.  Dynamic range is the difference, in decibels, between the quietest and loudest moments of a sound/show.  Setting a level for something with a high dynamic range is difficult.  A level appropriate for the quietest moment would easily clip and cause distortion during louder moments.  A moment for the loudest portion would render the quiet moments inaudible.  Many sound systems employ the use of compressors (and also gates which have a different but complimentary function) to reduce the dynamic range on the loud end. (Compressors literally compress the audio signal down after a certain volume, though they have a set of variable parameters such as at what decibel level they begin to do so and by how much.  Gates effectively mute a channel unless the incoming signal is loud enough to “open the gate,” again with a variable set of parameters.)

Unless you have incorporated such devices into your own sound system then YOU are the compressor.  As much as possible try and talk is a reasonable range.  If you are a person who talks with a great deal of range (ie you like to jump up and down screaming) then you should set your gain with extra headroom.  Headroom is difference between the nominal level and the peak level, the loudest level before clipping.  Think of this as a buffer for those moments of sudden outbursts.  The best thing to do here is to test yourself and your mic using the mic test feature.  Have a conversation with yourself and try to simulate your normal game play volume.  Then find a friend or 3 (or a random PUG) and have them give you some feedback about your mic settings.

There is however a negative feedback that we want to avoid.  A feedback loop is the result of a sound (usually isolated to a specific frequency range that happens to be more susceptible for a particular set up) being picked up by an input transducer (usually a mic), amplified by a sound system, sent out via a speaker (or more generally and output transducer) the resulting output being picked up by the initial input transducer. The result is a continually amplified signal that becomes painfully loud quite quickly.  A high frequency will sound “ringy” while a low frequency will produce a “rumble” effect.  Sometimes a sound is able to create feedback, but not consistently (usually because of the variance in level) in which case you will hear the beginnings of the feedback.

In DDO you are unlikely to actually create a feedback loop because the system is essentially a network of smaller systems.  The audio signal would therefore need to be transmitted through 2 or more systems continuously before a feedback loop can occur.  However, you have probably heard an echo effect as someone’s mic picks up someone else’s voice and then retransmits it, often times much louder since their system is amplifying the already amplified voice. We can apply the same principles of minimizing the potential for feedback to avoid this problem.

While there is a nice formula for calculating “gain before feedback” I will summarize it into 3 relationships that will decrease the likelihood of feedback.  If you envision a sound system you should recognize that you will have the following (with examples): a source (a person talking), an input device/transducer (a microphone), an output device/transducer (a speaker) and a listener (an audience or another input device).  This is also the order in which the sound travels.  The first relationship we are concerned with for feedback is the distance between the source and the input transducer.  We want this distance to be as small as possible (and mics in particular generally perform better at a closer distance anyways).  The second relationship is the distance between the output transducer and the listener and again we want that distance to be was small as possible.  Again, a speaker generally performs better at close range anyways.  The final relationship is the distance between the input and output transducers.  This time we want this distance to be as large as possible.  It also helps if the direction of the output is not in line with the pick up of the input – this is why you will see main speakers placed at the front of the stage instead of the rear.

If you think about it, this makes sense.  Sound volume deteriorates over distance.  If the input device is farther from the source, it will need to have a higher gain to pick up the incident sounds.  By the same token, speakers farther from the listener will need to be turned up to be heard.  This means that we are not only turning up the volume of the system, but its ability to pick up ambient and unwanted sound. These factors alone increase the potential of feedback, moving the input and output devices closer to each other only aggravates this problem.

A final note, your computer likely also has a master mic volume control that takes affect before DDO.  You may need to adjust these settings in addition to your DDO settings.  This will of course affect everything else on your computer that uses your mic input. You should first set your computer’s master level to accommodate programs without an individual volume control then make adjustments for programs that do with their controls.

If you’d like to read more on these subjects I recommend Sound Reinforcement Handbook by Gary Davis & Ralph Jones.  Much of the content here is covered in Chapters 3.5, 4.1 and 4.2