Yamaha N12 Owners Manual - Page 9
Recording Basics, Techie Words? Don’t Be Afraid., Signals - Level and Decibel - digital mixer
UPC - 086792859866
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Recording Basics Recording Basics English Techie Words? Don't Be Afraid. Signals - Level and Decibel Assume the softest sound a human being can hear is at a level of "1," and the loudest sound a human being can endure hearing is at a level of "1,000,000." The difference expressed in these numbers is huge, and you have to use too many digits to express the level. This is very inconvenient. So, we use a term or unit called "decibel (dB)," defining the normal level difference between the softest and loudest sounds detectable by human hearing to be 120 dB" A decibel is a relative value based on a reference level of 0 dB. Audio devices usually treat audio as electrical signals. There are various types of decibel measurements: dBu, dBV, dBm, etc., but the most popular one is dBu, which is based on 0.775V as the reference level (0 dBu). The output level of a microphone is very low -- about several millivolts (-60 dBu - -30 dBu). On the other hand, the maximum output of a mixer can be 12 V (+24 dBu). 0.775 V + 20 dBu 0 dBu -20 dBu Professional audio gear, such as a mixer or a power amplifier, features line inputs and outputs with a nominal level of +4 dBu. Keyboards and other line instruments have line inputs and outputs with a nominal level of -10 dBu. -40 dBu -60 dBu Microphone levels vary depending on the sound source. Speech is at about -30 dBu. Bird chirping is lower than -50 dBu. Closely recorded drums could reach 0 dBu. Mixers can handle signals of various levels. When you connect audio devices to your mixer, be sure to match the nominal input or output level of the connected devices. Many mixer inputs feature a "Gain" control. Be sure to use correct input jacks that will match the output level of the connected equipment. too low input signal appropriate level gain too high control output signal Balanced or Unbalanced? In most cases, shielded cables are used to transfer signals between audio devices. Shielded cables are divided into two types: balanced and unbalanced. Balanced lines are very good at rejecting noise, and they are the best choice for long cable runs or for transferring very weak signals. Unbalanced cables are usually used for line-level signals. Microphone: Use balanced lines. Short line-level runs: Unbalanced lines are fine. Long line-level runs: Use balanced lines. We are constantly surrounded by random electromagnetic radiation (noise), such as radio and TV signals as well as spurious electromagnetic noise generated by power lines, motors, electric appliances, computers, and other sources. The longer the wire, the more noise it is likely to pick up. To avoid noise, use the shortest cable possible. Anatomy of a shielded cable hot cold shield (ground) jacket balanced unbalanced As shown in the illustration above, a shielded cable consists of one hot (and cold conductor) wrapped in a metal net (shield, or ground conductor). The ground functions as a barrier against noise, protecting the signal from noise that may be induced in the line. How balanced lines work A cable that features an XLR plug on each end is a balanced line. It consists of hot (+), cold (-), and ground conductors. A device transmits an original hot (+) signal through the hot conductor and the same, but inverted, signal through the cool (-) conductor to the destination. The receiving device inverts the inverted signal back to normal and combines it with the original hot signal. Any noise induced in the line will be exactly the same in both conductors, and thus in phase. The trick is that the phase of one signal (through the cool (-) conductor) is reversed at the receiving end of the line so that the desired audio signals become in-phase, and the induced noise suddenly finds itself out of phase. The out-of-phase noise signal is effectively canceled while the audio signal is left intact. Owner's Manual 9