Tech Terms Demystified: Gain
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If you're like most people, when you hear the word "gain," what probably comes to mind is something along the lines of, "to get more, or increase in amount, magnitude, or degree." For a very old word, the definition of gain hasn't changed much throughout history and (surprisingly) the electrical definition is pretty darn close to Webster's. Given this agreement, you'd think understanding gain would be straightforward, but, like most terms used in consumer electronics, context is everything.
Gain covers a lot of territory:
- Antennas: radio frequency (RF) signal strength is measured as gain - i.e., the amount by which a circuit amplifies a signal. More gain means more amplification, which translates to higher signal strength (a high-gain antenna, for example, will amplify your TV signal so 1 watt of signal strength looks like say, 100 watts).
- Rear Projection TVs: light reflectivity is also measured as gain. Although gain still means "more," you don't get more light power, you get more light reflectivity. Better reflectivity means you get a better picture, and allows rear-projection TV screens to be larger and more energy efficient than TVs using plasma or LCD technology.
- Sound Systems: here it starts to get complicated. The word gain is used to measure signal amplitude, but describes more than one aspect of an audio signal:
- electrical amplitude measures signal strength - how powerful a signal is.
- audio amplitude measures signal level - how loud a signal is.
The amplitude of your incoming signal can be changed by adjusting the amplifier to pick up weak signals (or dial back an overly strong signal). This is done by changing the amp's input sensitivity, and the circuit that handles this is called a gain control.
Think of gain control the way you would an ear: when gain is set to "0", your amp isn't "listening" for a signal at all. As you turn the gain up, your amp starts paying more attention (becomes more sensitive) to incoming signal. Greater input sensitivity means more of the signal is picked up for amplification. Turning up the gain not only makes your sound more detailed, it gives your amp more electronic signal to work with. This translates to a more intense sound output (which our ears interpret as loudness) but it also means your signal is more likely to distort as you increase its strength.
To be effective, gain should be set when you install your system, then left alone unless something in your system changes. Many people equate gain with volume, but they work at opposite ends of the amplification process - gain affects signal input, volume affects signal output. Signal strength isn't increased when you turn up the gain, but the amp's ability to detect the signal as it comes into your amplifier is, so it pays to take the time to set your gain properly.