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BALANCED VERSUS UNBALANCED
If you become an audio engineer, sooner or later you will recognize differences between balanced and unbalanced audio equipment. A balanced line offers excellent immunity from hum, noise pickup, interference, and ground loops. Most professional recording studios use all balanced equipment. An XLR or a quarter-inch T/R/S (tip/ring/sleeve) connector usually indicates a balanced input or output (see Figures in Appendix B). A balanced line is used with microphones and high-quality line signals.
The Technical Part Is as Follows
Balanced lines typically have THREE wires used for a single signal. Pin 1 is usually ground, Pin 2 is HOT (+), and Pin 3 is COLD (−). A balanced line indicates that the signal-carrying wires are at equal potential, but opposite polarity. Balanced lines and cables are typically used in professional settings and can be run at very long lengths without accumulating noise.
An RCA connector or quarter-inch T/S (tip/sleeve) usually indicates an unbalanced input or output. Quarter-inch unbalanced lines are common with instruments such as electric guitar and bass, while RCA, or phono, is typically used with record players, speakers, and consumer stereo systems. This type of connector is also used to connect audio and composite video to TVs. They are often color-coded red for the right speaker and white for the left speaker. Unbalanced lines need to be kept short to avoid picking up interference or other unwanted noise. They typically are not effective at lengths over fifteen feet.
An unbalanced line has TWO wires, a HOT and a GROUND. The tip is HOT (+), whereas the sleeve is ground.
TIP
Some rack-mounted signal processors will allow you to switch between −10 and +4. This option is typically found on the back of the piece of equipment. If your studio is set up to be balanced, make sure that +4 is selected on all equipment. Select −10 if all your recording gear is unbalanced.
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MORE ON DECIBELS
Up to this point, we know that amplitude is measured in dBs. However, as you gain more experience in the coming years, you will come to know that there are many types of decibel ratings: dBs can describe power or voltage and sound pressure differences. Consumer and professional equipment not only differ in cost and perceived quality but also differ in the actual audio signal levels. Professional audio equipment generally has a normal operating level of +4 dBu, whereas consumer audio has a normal operating level of −10 dBV. Notice the change from dBu to dBV? Professional audio is about 12 dB hotter than consumer equipment. This difference in level can degrade audio quality in two ways:
1. If the output of the pro gear is plugged into the input of the consumer gear, the higher levels may overdrive the input, causing distortion.
2. If the output of the consumer gear is plugged into the input of the pro gear, the signal will be lower, which results in an overall lower signal-to-noise ratio and the input signal may be barely audible.
Decibels
dBFS − decibels at full scale. A dB rating associated with digital audio where zero is the maximum level. **−20 dBFS = 0 VU = +4 dBu** This is not a fixed standard.
dBu − professional rating +4 dBu = 0 VU = 1.23 Volts RMS and is used to express voltage levels.
dBV − consumer rating −10 dBV = 0 VU = 0.316 Volts RMS and is also used to express voltage levels.
dBSPL − decibels sound pressure level. Measures sound pressure levels relevant in our daily lives. This is the dB reference used mainly throughout the guide. 85 dBSPL = 0 VU = +4 dBu.