By Jonathan LippAn audio mixer is a device that combines from two to over a hundred audio input sources (microphones, recordings, instruments, etc.) into a "mixed" output. The mixer can further control each input’s relative level, to create an appropriate blend of the various inputs. Mixers (also called desks or consoles) come in different sizes, offer various configurations, and range from tens of dollars to tens of thousands of dollars (or even more).
Some mixers with few controls simply combine signals. Others may incorporate signal processing, send the audio signals to multiple destinations, recall specific settings or "scenes," include recording capabilities, or integrate power amps. Some even offer automation that remembers and plays back control changes. Many mixers have built-in preamps to raise the level of low-level signals (like microphones and musical instruments), but some—called line mixers or summing mixers—accept high-level signals only and forego the preamps.
With All Those Options, Where Do I Start?
The myriad mixer choices may seem overwhelming, but the good news is that there’s almost certainly one that matches your exact needs. So, begin by defining the mixer’s purpose. Next, decide what features will support that purpose, where the mixer will be located (portable or installed), and of course, determine your budget.
The Most Popular Mixer Types
We’ll cover special-purpose applications later. For now, let’s give overviews of the most common mixer types, and highlight some important features.
Sound Reinforcement for Live Performance
- Portability matters, because it simplifies transporting mixers to different venues.
- Reliability—failure is not an option for live performance.
- Versatility accommodates different mixing scenarios. One week you might mix a play, another week a concert, and another a panel discussion at a conference.
- Optional built-in recording provides a permanent record of what’s been mixed.
- The audience and the performers need separate mixes.
- Because the environment where you mix may be dimly lit, lighting is important.
Recording Studio
- Routing all the inputs and outputs needed by multi-track recording and playback is essential.
- Multiple outputs accommodate studio and control room monitors, headphone mixes, talkback to communicate with those being recorded, etc.
- Computer interfacing capabilities allow routing analog (or digital) signals into digital recording programs.
- Some mixers can serve as a physical control surface for the virtual mixers in recording software.
- Recording capabilities (all-in-one mixer/recorders) replace the traditionally separate mixer and recorder with a single, integrated device. This can save space and expense.
Field Mixing: Live Broadcast, Recording, Production
- Battery operation may be essential for some types of field recording. If so, look for the option to connect additional battery packs.
- A compact footprint is desirable for portability but may imply a minimal control set.
- Any device intended for field use needs to withstand adverse environments.
- Low-noise mechanical operation (do you really want switches that click?) avoids potential interference with what you’re recording.
- Some field mixers integrate on-board recorders and can be hand-held. The eliminates the need to bring extra recording gear.
Podcasting
Almost any mixer can mix microphones and other sources for podcasting, but there are newer designs optimized specifically for podcasts. They include features such as:
- Integrated recorders, or the ability to record directly to SD memory cards or flash drives.
- A USB interface. Depending on the design, this can send audio to other devices (computers or mobile devices), receive audio from other devices, or both.
- Bluetooth functionality provides a direct interface to mobile phones and tablets. The tradeoff is a few dozen milliseconds of latency (transmission delay).
- Memory to store sound effects, sonic logos, or phrases, and pad buttons to trigger them.
- Low-cut filters to remove low-frequency plosives and pops (called p-pops). These are generated by a blast of air hitting a microphone, like when you say the letters "p" or "b."
- Dynamic range compressors to even out the levels of microphones and other sound sources. This gives a more consistent, professional sound.
- Input limiting protects against momentary peaks that could cause distortion.
- When adding video to a cast, A/V-Mixers combine audio and video functions.
- Multiple headphone jacks let several people monitor the sound.
DJ (Disk Jockey), EDM (Electronic Dance Music)
This entirely different breed of mixer is more like a "mixing instrument" for DJs. The main characteristics are:
- Compact, with only 1 or 2 microphone inputs.
- Typically, 2 sets of stereo, line-level inputs for pairs of CD players, turntables, and other music sources.
- Both the main output and headphone outputs are fed by horizontal crossfaders. The DJ uses this to transition between 2 audio sources, as well as listen concurrently to the music being played and a source that’s being cued up for beat-matching.
- BPM (beats per minute) counters can act as references, or sometimes, derive the tempo from the music being played.
- Remote control for playback devices, like turntables.
- Some mixers can store sound effects or brief sections of music, with pads to trigger these sounds.
Special-Purpose Mixers for Specific Applications
The following mixer types still combine various inputs into one or more outputs, but are optimized for specific tasks, or include features that are pertinent only to a specific application.
Audio for Video Mixing
Features can include triggering presets for live and commercial breaks, and time-code synchronization with video switchers.
Installed Commercial Sound for Paging, Hospitality, and Restaurants
These offer screw-terminal connections, paging override, multiple zones, constant-on capability, and remote controllability. Some have built-in power amplifiers (described later).
Education, Conferencing, and Meetings
Because these mixers are mostly for voice, they have minimal controls. Features include automatic mixing, programmable muting for government chambers and courtrooms, and often, features to link to video conferencing systems.
Line Mixers, Summing Mixers
This type of mixer accommodates non-microphone audio sources, like electronic music instruments or multiple wireless microphones. Although "summing" is what all mixers do, in this case the term applies to mixers that usually have no extras (e.g., no onboard signal processing). They simply combine multiple digital and/or analog audio sources. When designed to be at home in set-and-forget applications, line mixers are typically rack-mounted, and forego linear-faders for space-saving rotary controls.
Broadcast Mixers for Radio and Television
For radio, mixers are optimized to put live content on-air quickly. They have features to cue and audition material before it gets fed on air. For television, microphones are less important. Instead, there are multiple sources for network feeds, playback of commercials, and station breaks, as well as links to video switchers for coordinated processes. Other features include remote control to trigger playback of commercial or program content and monitoring off-air.
Personal Mixers for In-Ear Monitoring
These compact mixers let performers create their own monitor mix for speakers or earphones. Personal mixers are usually either stand-alone systems fed by various mixer outputs, or accessories for digital mixers that integrate with the mixer’s networking capabilities. Performers can sometimes control personal mixers from a smartphone or tablet.
Mixer Features and Technology
Mixers can be as simple as 2 microphone inputs, 2 knobs to control their levels, 1 knob for overall output volume, and an output connector. However, most mixers have at least 4 to 8 inputs. Complex digital mixers can have dozens (and dozens!) of inputs, be totally reconfigurable, and integrate into facility-wide networks. How much complexity you need depends on the mixer’s purpose (you don’t need to pay for unnecessary features), and the experience and training of the operators. If they can’t figure out how to use a mixer’s features, there’s no point in having them.
Analog versus Digital
Analog mixers offer straightforward operation, because every function has an associated control. They can be less expensive than digital mixers, which are powerful and versatile. However, digital mixers often have too many functions to allow for individual, dedicated controls. Multi-function controls accommodate multiple functions but have more of a learning curve. Read more in our article on how to decide whether an analog or digital mixer is right for you.
I/O
I/O stands for Input/Output and represents what physical and electrical audio format(s) can connect to the mixer. Typical sources and destinations include line-level signals (line level is around 1 Volt). Most audio equipment, except for microphones (which produce about 0.001 Volt), operate at line levels. Wireless microphones often offer a choice of either microphone- or line-level signals.
Many modern mixers also have connections for digital audio formats, such as:
- S/PDIF: An optical or wired stereo digital audio interface used in consumer products
- AES/EBU: A pro-level version of S/PDIF
- ADAT: An optical interface that carries up to 8 channels of digital audio
- MADI: A high-end, multi-channel digital audio interface
Other digital I/O may include USB, Thunderbolt, or Ethernet for both audio signals and remote-control functions. Ethernet connections may feature standards like Dante, AES50/67 and Cobranet.
Note that a mixer with a USB output is not necessarily a "digital" mixer. For example, USB’s only purpose may be sending a final digital stereo mix to a computer. When reading spec sheets that list a mixer’s number of inputs or outputs, be careful that these inputs and outputs are compatible with the formats you plan to use—if you don’t have any gear that sends audio via an ADAT output, then you don’t need a mixer with an ADAT input. However, some companies provide optional-at-extra-cost cards or connectors for additional capabilities, like networking with a system. When assessing your needs, consider whether you might need a mixer that can expand its I/O capabilities.
Channels
Channels refers to input and output signals that the mixer can combine and route simultaneously. This specification is straightforward with traditional analog mixers, where each channel has a fader or knob to control the channel’s level. Digital mixers are more modular, so "channels" could refer to the physical number of inputs or outputs included in the mixer, or how many it’s capable of handling with optional hardware. Digital mixers may also use bank switching. For example, 8 faders could control 32 channels, but not all at the same time—only in groups of 8.
A mixer’s channels can be as simple as having one fader for volume, but most have controls for microphone preamplifier gain, equalization, stereo panning, channel mute, solo, routing buttons, and auxiliary sends. Some mixers (especially digital mixers) have multi-stage equalization, dynamics processors like compressors or gates, and delays. This reduces the need for outboard effects racks. Channels may also have their own meters, and electronic LCD "scribble strips" that describe the audio going through a specific channel.
Input Preamplifiers
Most mixer inputs accommodate both microphone and line-level signals and have variable gain controls to match the source’s level to the optimum level the mixer expects. Other preamp features include phantom power switching (to provide a power source to condenser mics), attenuator pad to prevent overloading the mixer with excessively strong signals, polarity (phase) switch, low-cut filter, and overload indicator.
Outputs
Mixer analog outputs are generally line-level. Some mixers have optional microphone-level outputs. These mixer outputs can plug into the microphone-compatible wall connectors found in hotel meeting rooms and convention centers.
Headphone Outputs
Most mixers have one or more headphone outputs, each with a separate volume control. This output may be the same signal as the main mix, although some can monitor different buses and solo different channels (see next).
Solo, PFL, AFL, SIP and Cue
These are variations on a useful set of features that allow the mixer operator to monitor isolated portions of the mixer. Typically, this is done through headphones in a live performance, or through speakers in a studio or during live setup. This kind of monitoring is essential for making adjustments, troubleshooting problems (e.g., listening to each channel individually to determine which one is creating hum), or auditioning a signal in advance of bringing it into the mix. A button on a channel, bus, effect or output will route that signal to the headphone or speaker outputs exclusively, in one of the following ways:
- Solo or AFL (After-Fade Listen) usually selects only the signal after the channel fader. Selecting more than one channel allows hearing multiple channels at once (e.g., just the channels for a brass section).
- SIP (Solo in Place) is like solo, but monitors the channel after any processing, and typically in a stereo field.
- Cue or PFL (Pre-Fade Listen) monitors a channel before the channel fader. This allows troubleshooting a channel with the fader down, so it’s not in the mix. Another application is cuing-up a source before adding it to the mix, like a recording or external feed. On broadcast mixers, the cue function is often a click-stop at the bottom of the fader (called down pot cuing), or a button that releases when the fader is advanced.
Buses
A bus is like a mini-mixer within a mixer, that can produce different variations on the mix. In a simple mono mixer, there’s only one mix bus—the one that provides a mixed output. However, most mixers can provide more than one simultaneous mix, routed to different outputs or internal processes.
The primary bus is the master bus, which is stereo (or much more rarely, surround). In live sound, this signal feeds the sound system that the audience hears. With recording, the master bus carries the final mix for distribution. Additional mix buses can route audio to different channels for multitrack recording, feed special effects like reverb, provide individual headphone mixes for musicians doing overdubs, or create separate monitor mixes for performers on stage or in the studio.
Routing audio to buses is controlled either by buttons, or separate rotary volume controls that send a channel’s signal to any combination of the buses. Auxiliary sends for monitoring are usually taken before the channel fader (pre-fader) so they are independent of the main mix, while effect sends are usually taken after the channel fader (post-fader). This way, the level of the effect changes in proportion to the channel’s level. Typically, each bus has a separate output control in the mixer’s output section, and their own output connectors.
Direct Outputs
These are outputs for individual input channels. The outputs bypass the mixer’s bus structure, which allows patching the audio at the channel’s input directly to other equipment, such as a recorder input.
Inserts/Send-Receives
Insert connectors break an input channel’s signal path. This makes it possible to patch external processors into the signal path.
Sends feed a channel’s audio, with variable level, to a bus. Receives (also called returns) have their own level controls and are where auxiliary buses return into the mixer after processing.
Groups
This feature creates a group of channels (called VCA or DCA groups) so that one fader can control all the channels in the group, such as all the mics used on drums, or a set of choir microphones. This simplifies mixing, because the relative volumes of each channel remain intact as you raise or lower the group’s level.
Mute Groups
This function allows muting certain channels with one button. For example, with a panel discussion, there could be a mute group for each mic that mutes all other mics. This prevents leakage and noise from other mics when they’re not being used. Another example is live events, where a mixer serves multiple functions (like mixing a band as well as a person giving a speech). One button can mute the band’s channels when it’s time for the speech.
Scenes, Cues
Digital mixers can memorize most mixer settings and recall them as a sequence of cues for a show or theatrical production. You could also recall settings for use at different shows or venues.
Wireless
Bluetooth connectivity provides an input for music sources like smartphones and tablets. This is useful for break music, or crowd control during delays. Some mixers have built-in Wi-Fi for external control.
Automatic Mixing
Automatic mixing is designed for meeting and conference applications. This function senses and controls the level of each microphone and adjusts the overall level to avoid feedback. Automatic mixing is available on some digital mixers and on mixers designed specifically for meetings.
Power Amplification
The line-level signal at mixer outputs is not strong enough to power loudspeakers. Separate power amplifiers usually insert between mixers and speakers, but some mixers have built-in amplifiers for convenience and portability. You’ll find two main options:
- Powered mixers, which are portable mixers for live sound applications.
- Mixer-amplifiers are part of permanent, commercial sound system installations for paging, background music, and meetings. These are found in offices, hotels, restaurants, and businesses. Most mixer-amplifiers (also called package amps) have both 8-ohm outputs and high voltage/high impedance 70-Volt outputs for attaching many sets of speakers. Features include priority muting/ducking, interfaces for phone systems, and alert tones.
Control Surface
Control surfaces are not necessarily mixers but can control digital mixers or a DAW’s virtual mixer with hardware—hands-on faders, knobs, and buttons. Some digital mixers also offer control surface functionality, which is particularly useful with computer-based mixing. Make sure you check for compatibility between the control surface and the device or software being controlled. There are two main standards: HUI (Human User Interface) and Mackie Control.
Power Supply
Although most mixers have a built-in AC power supply, some are external. Given that power supplies are more prone to failure, especially in the field where power systems are prone to voltage spikes, an external supply’s main advantage is that it’s easy to carry a spare for replacement. Another is that you can carry a supply for compatibility with different electrical standards (e.g., 110 vs 220 Volts). Some higher-end mixers have redundant supplies for maximum reliability.
If you find mixers daunting, don’t worry—help is on the way. The Full Compass experts can analyze your needs and match them to the right mixer for your requirements and your budget. Give us a call, and we’ll discuss the various options for your application.
By Jonathan Lipp, Founder Full Compass
Acknowledgement: Thanks to Craig Anderton for editing and additional insights.