The mixer provides the control function of the audio for a sound system allowing inputs to be connected and processed while providing outputs for the main out and auxiliary output through buses and groups.
Key Mixer Terms
Channels – A channel accept mic and/or line level and provides a preamp to raise that input up to an appropriate level for processing thru the mixer. Each channel will provide a processing section that will include equalizer section, routing section that will include sends to buses and returns from effects. Lastly the pan control and fader for the main output section.
Buses – Each channel will pass the signal to one of more buses. The main output is connected to the master mix bus, which is fed by the channel faders. The auxiliary bus (aux send) is fed by a separate volume control on each channel and assigned to an output jack on the mixer. Aux buses can be selected from multiple sources within each channel for different needs of the application. These selections include preEQ, postEQ, pre-fader or (post-fader). These special outputs are useful for monitor mixes, headphone mixes, recording mixes, and as effects sends. Most mixers today provide dedicated bus for aux send just for effects, which may include an onboard effects processor or dedicated return channel.
Groups – Large-format mixers feature channel grouping that is useful way to manage large numbers of channels. Each group matrix provides a dedicated mix for different application. A mix may be provided with all of the drums to Group 1 and all of the vocals to Group 2. Each group with an output fader allowing the feeds into the master buss. This provides control of an entire sections of the mix with one fader without affecting each channel within each group.
Inserts and Direct Outputs – Channel inserts points are between the preamplifier and the EQ section for each channel and uses a TRS cable with shared common. These inserts are ideal for adding outboard processors such as a noise gate, compression and parametric equalization to individual channels. By contrast, direct outputs simply send a copy of the preamplifier signal out of the board, which makes them useful for sending individual feeds to an external mix for recorder or audio interface.
Analog and Digital Mixers
Analog Mixers – In an analog mixers, discrete component are comprised of physical circuitry (e.g., resistors, capacitors, inductors, op amps, potentiometers, switches and wire) to provide the preamps, equalizers, and other functions within the mixer.
Digital Mixers – After the board input preamp, the analog signal is converted into digital data for processing and routing. Digital mixers offer a number of cost effective conveniences analog mixers don’t. To start, dynamic signal processing for each channel that provides phasing, high pass filtering, noise gating, parametric equalization, compression and delay functions. Each output function is provided with dynamic signal processing that includes compression and graphic equalization. In addition some mixers also provides parametric equalization and delay.
With the digital technology comes the advanced features such as Ethernet integration, WiFi networking with laptops and tablet PC’s for interfacing the controls. And when you take into account the generally higher sound quality they offer, it’s little wonder that digital mixers have become standard live sound gear. Digital mixers come with steep learning curve but with PC-Based large screens and the remote control capabilities with tablets far out way the these limitation. Other features includes the rack mount version that requires less equipment is overwhelming.
Line Mixers – Line mixers are analog mixers that deal exclusively with line-level signal. They provide only a single volume control per channel. Allows the combining of multiple sources into a single output. These are sometimes summing mixers to assist in providing the final mixes.
What to Look For In a Mixer
Channels and Inputs
- How many do you need?
- Include stereo inputs for keyboards
- Direct inputs for bass and guitar
- Keep future expansion in mind.
- Basic mixers provide a 3-band equalizer with a 12 kHz high shelving, 400-8k Hz sweepable midrange filter and a 80 Hz low shelving filter.
- The next level mixer provide a 4-band equalizer with a 12 kHz high shelving, 100-8k Hz sweepable upper midrange filter, 100-2k Hz sweepable lower midrange filter and a 80 Hz low shelving filter. this is the minimum recommended to address the two major sweet spots of any one mixer input.
- The next option would be an outboard parametric equalizer on the insert of each channel to provide a 5 band equalizer for greater control of your mix.
- The channel insert is post-High Pass Filter and pre-EQ. This is a line level to work with signal processing equipment such as gates, compressors, parametric equializer and delay units.
- The direct outputs provide a useful source for multi-mix applications. This output is provided as a pre-fade output with no effect from the live mix. Another application for this function is channel effects sends using a post-fade for dedicated reverb unit for that channel. This is done to up the an aux send for other purposes.
Onboard Processors and Effects
FX Sends are provided to send a portion of a selected channel to the effects processor. This can be on-board effects as well as off-board devices. Two to four send are provided depending on the model you are considering.
With the FX Sends to off-board equipment there will be FX Returns provided back to the main bus or mix. Aux output can be used for this same purpose.
Buses and Routing
Starting with busing options a typical minimum would be 5 buses that include:
- Main bus would be 2 (left and right)
- Aux bus count of 2
- PFL (Pre Fade Listen)
The high-end equipment may include about 15 buses that include:
- Main bus with 3 (left, right and mono)
- Aux bus count of 6
- Group buses with a count of 4
- PFL (Pre Fade Listen) / AFL (After Fade Listen)
AUX SENDS used for feed to stage monitors as well as special applications such as recording, zone feeds, clean feeds and aux fed subs. Factory default settings should satisfy the most common applications:
- AUX1, AUX2 = Pre-fade (Pre-fade aux = Pre-INSERT, pre-EQ, post-MUTE)
- AUX3, AUX4 = Switched pre/post using PRE switch
- AUX5, AUX6 = Post-fade
These settings may be changed with the internal jumper link options.
Groups are provided on the high end mixer to provide for easy control of a groups of inputs which allow for the group functions such as compression, equalization or effects. these groups can then be sub-mixed back into the main for final routing.