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Phần 4: Sound Mixer.
Sound Mixers: Overview
A sound mixer is a device which takes two or more audio signals, mixes them together and provides one or more output signals. The diagram on the right shows a simple mixer with six inputs and two outputs.
As well as combining signals, mixers allow you to adjust levels, enhance sound with equalization and effects, create monitor feeds, record various mixes, etc.
Mixers come in a wide variety of sizes and designs, from small portable units to massive studio consoles. The term mixer can refer to any type of sound mixer; the terms sound desk and sound console refer to mixers which sit on a desk surface as in a studio setting.
Sound mixers can look very intimidating to the newbie because they have so many buttons and other controls. However, once you understand how they work you realize that many of these controls are duplicated and it's not as difficult as it first seems.
Some of the most common uses for sound mixers include:
- Music studios and live performances: Combining different instruments into a stereo master mix and additional monitoring mixes.
- Television studios: Combining sound from microphones, tape machines and other sources.
- Field shoots: Combining multiple microphones into 2 or 4 channels for easier recording.
Mixers are frequently described by the number of channels they have. For example, a "12-channel mixer" has 12 input channels, i.e. you can plug in 12 separate input sources. You might also see a specification such as "24x4x2" which means 24 input channels, 4 subgroup channels and two output channels.
More channels means more flexibility, so more channels is generally better. See mixer channels for more information.
The diagram below shows how a mixer can provide additional outputs for monitoring, recording, etc. Even this is just scratching the surface of what advanced mixers are capable of.
Sound Mixer: Channels
Each input source comes into the mixer through a channel. The more channels a mixer has, the more sources it can accept. The following examples show some common ways to describe a mixer's compliment of channels:
12 input channels.
16 input channels, 2 output channels.
24 input channels, 4 subgroup channels and two output channels.
On most sound desks, input channels take up most of the space. All those rows of knobs are channels. Exactly what controls each channel has depends on the mixer but most mixers share common features. The list below details the controls available on a typical mixer channel.
Input Gain / Attenuation: The level of the signal as it enters the channel. In most cases this will be a pot (potentiometer) knob which adjusts the level. The idea is to adjust the levels of all input sources (which will be different depending on the type of source) to an ideal level for the mixer. There may also be a switch or pad which will increase or decrease the level by a set amount (e.g. mic/line switch).
Phantom Power: Turns phantom power on or off for the channel.
Equalization: Most mixers have at least two EQ controls (high and low frequencies). Good mixers have more advanced controls, in particular, parametric equalization.
Auxiliary Channels: Sometimes called aux channels for short, auxiliary channels are a way to send a "copy" of the channel signal somewhere else. There are many reasons to do this, most commonly to provide separate monitor feeds or to add effects (reverb etc).
Pan & Assignment: Each channel can be panned left or right on the master mix. Advanced mixers also allow the channel to be "assigned" in various ways, e.g. sent directly to the main mix or sent only to a particular subgroup.
Solo / Mute / PFL: These switches control how the channel is monitored. They do not affect the actual output of the channel.
Channel On / Off: Turns the entire channel on or off.
Slider: The level of the channel signal as it leaves the channel and heads to the next stage (subgroup or master mix).