In-ear monitors (IEMs) are devices used by musicians, audio engineers and audiophiles to listen to music or to hear a custom crafted mix of vocals and stage instrumentation for live performance or recording studio mixing. They are often custom fitted for an individual's ears to provide comfort and a high level of noise reduction from ambient surroundings.
A monitoring system is any system that provides a mix of audio sources to a performer on stage. Traditionally, monitors were loudspeakers placed on stage directed toward the performer (often called floor monitors or wedges). Depending on the sophistication of the audio system, they may be more distracting than helpful to their singing. Since performers wear an IEM in each ear, they can also hear a stereo mix if a particular monitor system allows it. This can allow additional definition of the audio by panning different elements to each ear. Recent advances in this technology also allow the user to incorporate an ambient feature, allowing them to adjust the amount of ambient noise filtered by the IEM.
One additional consideration for mixing IEMs is that while getting rid of floor wedges can improve the overall clarity of the mix for the performers and decrease the overall volume on-stage, one important piece that is often lost is crowd noise. It is not uncommon for a microphone to be placed near each side of the stage, facing out to the audience, to provide a way to get some of the crowd noise back into the performers' IEM mixes. Larger live shows could have several microphones for this purpose spread across the front of the stage, which could also be sent to a multitrack recording device used in an outside broadcast production truck, or other destinations.
Transmitter and receiver
The most common professional stage in-ear monitor system employs the use of a wireless system to send the mix to the IEMs. This system contains a transmitter and a receiver pack that is worn by the performer. There is generally a transmitter for each monitor mix and there is always a receiver for each IEM. The transmitters usually output either one stereo mix or two mono mixes. When the transmitters are set up for two mono mixes, one transmitter can be used for two different mixes. Any number of receivers can receive a single mix. The output from a receiver is generally too weak to power two monitors at the same time.
The transmitters and receivers transfer audio wirelessly via a VHF or UHF radio frequency. Generally speaking, UHF systems sound much better than VHF systems and are therefore more expensive to purchase. UHF systems usually are less susceptible to frequency interference which adds to their level of quality.
The in-ear monitors themselves are the last stage of the signal path in the system. The IEMs are often custom molded and therefore are more comfortable to wear and allow the sound to be sent directly into the user’s ear canal. They also provide a better seal, though it is only able to isolate ambient noise, thus resulting in a lower level of ambient noise heard. Depending on the quality of the fit and length of the canal portion of the earpiece, a custom fit in-ear monitor will generally provide somewhere between 25 and 34 Decibels of noise reduction. Custom in-ear monitors come in a variety of colors but usually are clear or a color that closely matches the skin color of the performer. Some manufacturers can also place custom artwork directly on to the custom in-ear monitors. The IEM cable plugs into a 3.5 mm stereo jack on the receiver pack; typically clipped onto the belt, guitar strap, clothing of the performer, or placed in a pocket. Non-custom IEMs are also available and include a variety of universal foam and silicone tips that will fit into most people's ears.
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