Yamaha MG124CX Owner's Manual - Page 8

Mixer Basics Making the Most of Your Mixer You've got yourself a mixer and now you're ready to use it. Just plug everything in, twiddle the controls, and away you go ... right? Well, if you've done this before you won't have any problems, but if this is the first time you've ever used a mixer you might want to read through this little tutorial and pick up a few basics that will help you get better performance and make better mixes. Balanced, Unbalanced-What's the Difference? In a word: "noise." The whole point of balanced lines is noise rejection, and it's something they're very good at. Any length of wire will act as an antenna to pick up the random electromagnetic radiation we're constantly surrounded by: radio and TV signals as well as spurious electromagnetic noise generated by power lines, motors, electric appliances, computer monitors, and a variety of other sources. The longer the wire, the more noise it is likely to pick up. That's why balanced lines are the best choice for long cable runs. If your "studio" is basically confined to your desktop and all connections are no more than a meter or two in length, then unbalanced lines are fine-unless you're surrounded by extremely high levels of electromagnetic noise. Another place balanced lines are almost always used is in microphone cables. The reason for this is that the output signal from most microphones is very small, so even a tiny amount of noise will be relatively large, and will be amplified to an alarming degree in the mixer's high-gain head amplifier. Balanced noise cancellation To summarize Noise Microphones: Use balanced lines. Phase inversion Hot (+) Cold (-) Ground Source Cable Phase inversion Noise cancelled Receiving device Noise-free signal Short line-level runs: Long line-level runs: Unbalanced lines are fine if you're in a relatively noise-free environment. The ambient electromagnetic noise level will be the ultimate deciding factor, but balanced is best. Signal Levels and the Decibel Let's take a look at one of the most commonly used units in audio: the decibel (dB). If the smallest sound that can be heard by the human ear is given an arbitrary value of 1, then the loudest sound that can be heard is approximately 1,000,000 (one million) times louder. That's too many digits to deal with for practical calculations, and so the more appropriate "decibel" (dB) unit was created for sound-related measurements. In this system the difference between the softest and loudest sounds that can be heard is 120 dB. This + 20 dBu 0 dBu -20 dBu 0.775 V Most professional mixers, power amplifiers, and other types of equipment have inputs and outputs with a nominal level of +4 dBu. The inputs and outputs on home-use audio gear usually have a nominal level of -10 dBu. is a non-linear scale, and a difference of 3 dB actually results in a doubling or halving of the loudness. You might encounter a number of different varieties of the dB: dBu, dBV, dBM and others, but the dBu is the basic decibel unit. In the case of dBu, "0 dBu" is specified as a signal level of 0.775 volts. For example, if a microphone's output level is -40 dBu (0.00775 V), then to raise that level to 0 dBu (0.775 V) in the mixer's preamp stage requires that the signal be amplified by 100 times. -40 dBu -60 dBu Microphone signal levels vary over a wide range depending on the type of microphone and the source. Average speech is about -30 dBu, but the twittering of a bird might be lower than -50 dBu while a solid bass drum beat might produce a level as high as 0 dBu. A mixer may be required to handle signals at a wide range of levels, and it is necessary match input and output levels as closely as possible. In most cases the "nominal" level for a mixer's input and outputs is marked on the panel or listed in the owner's manual. 8 MG124CX/MG124C Owner's Manual