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What Mixers Are Used with PA Systems?

Mixers are items of equipment that arrange multiple input audio signals in a suitable balance, and they adjust tone quality so that the output audio is easy for the audience to listen to. There are many types and models of mixer.

Types of mixer

Mixers are broadly classified into three types, based on their internal structure.

(1) Analog mixers

Analog mixers adjust the volume and tone of input audio signals. Most of the control knobs and faders are arranged on the top panel, so it is easy to understand the signal flow and what state the audio is in. Operating analog mixers is normally an intuitive process.

(2) Digital mixers

Digital mixers process input audio signals and adjust their volume and tone using digital signal processing technology. Various kinds of tone control that would be impossible using analog equipment can be applied using digital processing. Digital mixers can store the positions of faders and knobs, and recall these positions in an instant. The faders and knobs perform various functions, so the unit itself remains compact, even if the number of channels increases. Generally a digital mixer will require more experience to set up effectively, but will offer far greater functionality than an analog mixer.

(3) Powered mixers

Powered mixers are analog mixers with built-in power amplifiers. For this reason, sound can be played with the mixer directly connected to speakers. In cases where the same equipment is always connected, powered mixers can be used by simply turning the power on, so operation is simplified and convenient.

Reference: All-in-one PA systems

All-in-one PA systems consist of a powered mixer, speakers and speaker cables. They are easy to configure, easy to carry due to their light and compact format, and suited to small events and band lineups.

Input channels

Number of microphone input and line input channels

The number of input channels in a mixer is extremely important, as this indicates the number of microphone and musical instrument signals that can be handled. In addition to the number of input channels in a mixer, it is also important to consider such factors as how many of those input channels are for microphones, whether line input channels are monaural only, and whether inputs will accept stereo signals.

For example, when using a mixer with a band, at least eight channels for input may be required for microphones to pick up the sound of the whole drum kit. In this case, a model that is equipped with enough channels that are compatible with microphones should be chosen.

A mixer with many stereo channels is useful for connecting multiple devices that output stereo signals, such as synthesizers. Likewise, a mixer that has built-in effectors, such as compressors or reverberation, is recommended for situations where audio such as vocals will be input. Finally, a mixer that is able to connect to a personal computer via USB is recommended for home studio applications.

Differences between microphone input and line input

- Microphone input channel

Audio signals picked up by a microphone are very weak, so they must be amplified by using the head amplifier (GAIN) of the mixer. Connect to the MIC connector.
Note: Phantom power (often labelled as "+48V") is required when using a condenser microphone.



- Line input channel

Line level devices such as keyboards and CD players are connected to the LINE connector.

Generally, phone connectors and RCA pin connectors are used in this case.

When both MIC and LINE inputs are available on same channel, use the LINE connector. When the same connector is used for both MIC and LINE, reduce the level by pushing the PAD button so that audio is not distorted (Remember line signals have a higher level than mic signals).



Tips

Sometimes a combination jack is used as both a microphone and a line connector. Activate the PAD when using a line input, to avoid distorting the louder signals.

Mixer Functions

This section describes how to adjust the audio of each channel

(1) Equalizers

Mixers are equipped with equalizers that adjust the tone of each channel. Some equalizers have just 2-bands, which can adjust lows and highs. Some are 3-band equalizers, which modify the sound by boosting and cutting lows, mids, and highs. And some 3-band equalizers include a MID-sweep, which can modify the mid frequencies which characterize most musical instruments and voices. The more frequency bands there are, the more detailed the sound production can be.

Knob Characteristic Affected sounds Boost Effect Cut Effect
HIGH 10 kHz (+/- 15 dB) High overtones exceeding the register of the instrument. Crunchy, metallic echoing increases, and the tone becomes sharp. If boosted too much, will sound noisy. Tones become smooth. "S" noise canceling is effective. If cut too much, high range transparency will be lost.
MID 3 kHz (+/- 15 dB) Instrument/vocals high registers Sound becomes bright and hard. Sound becomes modulated and bright. If boosted too much, sound will become unpleasant. Audio balance tends toward lows. If cut too much, audio will become dark.
1 kHz (+/- 15 dB) Instrument/vocals medium registers. The outline of the audio can be made clear. Audio sounds as if it is projected forward. Emphasizes the attack of toms and bass drums. Tones become rounded and pleasant. Sounds are more muffled and no longer stand out in the mix.
500 Hz (+/- 15 dB) Instrument/vocals medium-low registers. The sound becomes thicker and more powerful, and tonal balance tends toward lows. If boosted too much, the sound becomes unnatural, as if it were coming out of a telephone. The sound becomes hard and has a feeling of attack. Tonal balance tends toward highs. If cut too much, the sound becomes thinner.
LOW 100 Hz (+/- 15 dB) Instrument low registers. The sound becomes rounder and deeper, giving it more strength and a sense of scale. If boosted too much, the sound becomes less crisp. The sound takes on a lighter quality, improving its crispness. Floor noise or howl canceling is effective.

(2) HPF (High Pass Filter)

The HPF cuts unnecessary low frequencies at the input. Most microphone and mic/line inputs have an HPF function, but some dedicated line inputs may not.

HPFs are often used for hi-hat, snare, and vocals to cut unnecessary low frequencies and therefore create a cleaner sound. They are also used to eliminate unwanted popping noises when picking up voices, such as during speeches.

(3) Pan

This adjusts the output ratio when playing audio from left and right speakers. It is used to widen the sound image, or to position each input relative to their location on the stage. Audio for stereo channels is already set in the stereo image, so a BAL control is used to adjust the balance between the left and right speakers.

(4) Level Faders/knobs

These adjust the volume of each channel, group, stereo output, etc. Fader-type controls allow for quick operation. Though some mixers use knob-type volume controllers.

How to output audio from the mixer?

Mixers can output various separate channels of audio, depending on the needs of the event, such as sending audio meant for the audience to the main speakers and audio meant for the performers to the monitor speakers on stage:
STEREO OUT is normally used to send signals to the audience; AUX SENDs for performers' monitor speakers and external devices; MONITOR OUT is for monitor speakers used when mixing audio in the studio; GROUP OUT for outputting several signals together; REC OUT for connecting with recording devices; and PHONES for connecting headphones.

(1) AUX bus

The AUX bus is a circuit used to send signals to external devices. It can be used to send signals to performers' monitor speakers separately from the main output, or to send signals to external effects and recording devices. A mixer with many AUX sends should be chosen if there are many people in the band or if separate monitor signals with individual balances need to be sent to the performers.

(2) GROUP bus

The GROUP bus is a circuit for controlling multiple channels at once. For example, if there are eight microphones (for eight channels) placed around a drum set and you want to raise or lower the volume of the entire set, it would be difficult to accurately raise or lower the faders for all eight channels. If these channels are all set to a single group, the volume of the entire drum set can be raised or lowered, while maintaining the same balance, merely by raising or lowering the fader for the group.

(3) STEREO bus

The STEREO bus is a circuit for combining each input coming into the mixer or each GROUP bus signal, adjusting the overall level, and outputting the audio through stereo output connectors.

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