You can learn, review, and apply the basics of mixing in this feature column. Whether you are thinking about buying your first mixer, mixing virtually with software, or just want to review some of the terms and concepts, this is a great place to start! The Alesis MultiMix series has many different options from a straightforward analog mixer to feature-packed consoles with built-in digital audio interfaces and advanced routing options for recording.
WHAT IS A MIXER?
In addition to blending and balancing the relative level of each source, a mixer may enable you to shape other audio characteristics of the individual sources or the final output including tone using equalization (EQ) and left/right stereo balance using pan controls, and even more radically alter sounds by processing them with effects that may be built into the mixer or externally connected.
Finally, mixers enable you to output your mix a variety of ways. Most mixers have at least a master output and a headphone (or cue) output. Many also have additional outputs that can enable you to send your mix out for processing in external devices, group a segment of input sources, send a special mix to the studio’s control room, or send a specific mix to a monitor or foldback system.
Some advanced mixers also have analog-to-digital converters and special outputs for connection to computer recording systems via USB, FireWire, or other specialized connectors. Alesis MultiMix USB, MultiMix USB 2.0, iMultiMix USB, and MultiMix FireWire mixers all fall into this category.
FOLLOW THE SIGNAL
Perhaps the most important concept to understand when looking at mixers is signal flow. This term refers to the way the audio signal flows through the mixer from input, through any processing and routing on its way to the output. On most mixers, the controls are arranged in columns called channels. You can follow the signal flow on each channel from top to bottom. The signal comes in at the top and as the signal flows down, you have opportunities to manipulate it with each control section. Keeping this top-to-bottom flow in mind, any changes you make to the audio in one section will affect the audio before it hits the section below it (with some exceptions such as post-fader AUX sends). Let’s take a look at an example.
A channel on the MultiMix 8 USB has the following features:
- Input connections – this is where you connect the microphone, instrument, or other source
- High-pass filter – switching this on attenuates frequencies lower than 75 Hz, such as wind noise or handling noise
- Gain control – this adjusts the level of the preamplifier (for more, check out Gain Staging 101)
- High, Mid, and Low EQ controls – you can cut or boost different parts of the frequency spectrum to shape sound with these knobs
- Aux send level controls – these controls determine the level of the signal that you send to processors (such as reverbs and compressors) that are connected to the mixer’s Aux inputs or built in
- Pan control – control left/right stereo balance
- Level control – this control enables you to set the level of the channel that is sent to the output section. It is often manipulated using faders on larger mixers, or knobs on compact mixers like the MultiMix 8 USB.
The Mic/Line/Guitar input selection button built into channels one and two of some MultiMix models is for switching the preamplifier to the right level to work with the kind of signal you are plugging in. All electronic instruments and microphones have a degree of impedance, or resistance to the signal flowing. Electric guitars have higher impedance than line-level sources such as a keyboard and have significantly higher impedance than most microphones. That means we need to amplify the signal to a greater degree to wind up with a usable level. If you’ve ever tried to plug your guitar into a keyboard amp and wondered why it sounded so wimpy, mismatched impedance is the primary reason. Microphone impedance varies from 150 to 10,000 ohms, so that’s why mixers and mic. preamplifiers have adjustable gain knobs.
The Gain control is the first gain stage of the mixer. It can shape the quality of the incoming audio and should be set based on the level of the sound source. The Gain control on the Alesis MultiMix series gives you more than enough headroom to work with almost all kinds of microphones and instrument sources. Think of the Gain control as the main faucet for a garden hose. If there is only so much volume allowed through at the faucet, or Gain knob, you cannot reliably add more volume later. Conversely, if you turn it up too high, you run the risk of distortion and other issues. This is like hooking your garden hose up to a fire hydrant.
Once the signal finishes passing through the channel strip, now you can think of it moving left to right, from the channel to the output section. In the output section, you can specify what is sent to the main output, what is sent to the headphone or control-room monitors, and what is sent to the alternate, buss, or monitor outputs if you mixer has those.
For some gain basics, be sure to review Gain Staging 101. When first configuring a sound source with a mixer, start with the level knob/fader at minimum setting (- or ∞). This is to avoid dangerous pops, feedback, or volume spikes when connecting sound sources that can damage your speakers or your ears. We recommend that you keep the mixer and speakers off while connecting inputs. Once everything is connected, you can turn on the mixer and speaker system, but make sure the Master output fader or knob is all the way down.
To find the best settings for your loudspeaker setup and the Main Mix of the mixer, when you first get to the venue or first set the mixer up in your studio, play some familiar and well-mastered music through the system by connecting a CD player or iPod (iPod volume should be roughly 85%) to the 2-track RCA inputs (also known as Tape In). This special input, included on our entire line of MultiMix mixers, is a fixed-level input for line-level gear. Press the 2-TK TO MIX button and set the Main Mix level, starting with halfway and working in either direction.
The next step is to set the amount of gain that is appropriate for each source. Start with the Gain control at the 12 o’clock position. If the channel Peak LED starts to light while you test the mic or instrument with loud material, turn the Gain down. If the volume seems low, don’t worry about turning the Gain up yet.
Managing gain is the most overlooked process to creating great mixes. Too much gain at any point in the signal chain can cause distortion, clipping, muddiness, harshness, feedback, or lack of control of the sound. Too little gain can cause you to compensate at some point in the chain, resulting in audible line noise, dangerously high volume settings leading to feedback, pops, or loud spikes when other sources are introduced or a dirty cable is wiggled. This is why starting with the halfway point is ideal.
Now let’s set some channel levels.
- Slide the channel fader to unity gain (0).
- Turn the AUX SEND and GAIN controls all the way down and turn the EQ knobs to the center detent (you’ll feel a click)
- Press the PFL / SOLO switch on the channel
- Make sure the SOLO MODE switch in the master section is set to SOLO
- Play the instrument at a normal level and watch the meter (LED tree)
- Adjust the channel’s GAIN knob until the LED meters remain at or very close to 0
- If you need to apply EQ, do so and check the meters again
- Repeat for each channel
MultiMix mixers give you three bands of EQ per channel: high shelving at 12 kHz, mid bandpass/reject at 2.5 kHz, and low shelving at 80 Hz. Using these knobs, you can tailor the channel’s signal by boosting some frequencies and cutting others. The LO and HI controls are shelving EQs with fixed frequencies of 75 Hz and 12 kHz, while the MID control has a peaking response fixed at 2.5 kHz. Shelving means that the mixer boosts or cuts all frequencies past the specified frequency. Peaking means that the mixer boosts or cuts a range of frequencies with a certain width and a central Q or peak point.
“Two examples of peaking EQ”]
“Two examples of shelving EQ”]
If you are using your mixer for recording, be subtle with the EQ settings or don’t use them at all. Too much EQ can cause permanent damage to the sonic quality of a recorded track. You can always apply EQ later, but you can’t undo any sound-manipulation you do in tracking. Some of the best recordings are done with no EQ at all! Always use EQ as a finesse tool. If you are not getting the sound you want, move the microphone(s) first, and then experiment with other particulars of the sound source you are recording. Mic choice and placement on speakers, drum heads, and acoustic guitar bodies is a critical part of fine-tuning a recording. Also experiment with location in the room. Try not to use EQ as a means of fixing a badly miked source. A useful tip you will find only on our iMultiMix line of mixers, is the ability to EQ your docked iPod through the mixer. We've assembled details on this procedure for you here.
Another good tip on EQ for both live and studio application is to reduce frequencies that are causing problems with the mix rather than amplifying others to cover the problem. Let’s say you are miking a drum kit in a large room. You probably want the kick to have the classic chest-pumping thump without boxiness. Solution: take out the boxiness with EQ. Boxiness is a vague audio engineering term describing lower midrange frequencies which, when overly abundant, overwhelm a well-rounded representation of the source. Rather than boosting the LO, you’d reduce the MID and then turn the channel level up a bit to make up for the frequency loss. Turning the channel up with the midrange frequencies reduced will bring out the “good” frequencies in a more favorable relation to the “bad” and have the effect of adding low and high end without causing distortion or muddiness. If you still want some low-end thump at this point, add a few dB of low. Try 1-3 o’clock on the LO knob. Any more than this and you are may cause distortion and muddiness. Assuming the drum sounds acoustically the way you expect, you may need to move the mic, adjust placement in the room, or you may want to try a mic better suited for kick drums.
Most mixers contain several options for routing audio channels. An audio buss is signal-routing option to which you can send one, some, or all channels. For example, you can choose to send the lead vocal to the Main or Master Buss, Aux Buss A, neither, or both. There are a variety of ways to use an audio buss on a mixer, but most commonly you’ll use the Main/Master Buss to feed the house PA system, a Record buss to feed a mnultitrack recording system, and Aux busses for sending a portion of the final mix to an externally connected effect unit or to stage-monitor setups.
Another way that busses are used is for grouping a set of channels together. For example, you might put the entire drum set on an Aux buss which will let you run the entire drum set through an effect without impacting the rest of the mix.
Using Outboard Effects with Aux Buss A
Here’s an example of a typical effects loop with a reverb or delay unit and mixer.
1. Connect a cable from your mixer’s Aux Send A to the Left (Mono) input of a MidiVerb 4
2. Connect a cable (or two for stereo effects) from the MidiVerb’s outputs to the mixer’s Aux Return A (Left or Left/Right)
3. Set the MidiVerb 4 inputs and outputs to at least 75%
4. If you are adding effects to vocals, while checking the mic with authority (loudly), slowly turn the Aux Send A up on the mic’s channel on the mixer. You will see the MidiVerb 4’s input meters responding more and more as you do. Stop when the meters reach around 90%. Never allow the meters to reach the max, as it can result in digital clipping.
5. Slowly turn the mixer’s Aux Return level up until you start to hear the effects come through. The Aux Return is likely the only knob you will be reaching for once you’ve set the levels and effect as desired.
Using Internal Effects with Aux Send B
On MultiMix mixers with internal effects processors, Aux Send B feeds the effect-section’s input. To keep it simple, just turn the Aux Send B to halfway and slowly turn the Aux Return B (effects level) up to hear the effects applied to the channel you’ve turned the Aux Send B up on. To choose the effect you want, turn the effect selector knob and click it in. If you attach a cable to AUX Send B, you disable and bypass the onboard effects and turn Aux Buss B into a standard Aux buss, which you can use identically Aux Buss A.
Using Aux Busses for Monitoring
Using one or more AUX sends for monitoring purposes give you the ability to individually control how much of each channel is fed to headphones or stage monitors. Mixers with multiple AUX busses enable you to create multiple monitor mixes so, for example, you could give the singers lots of vocals and guitar, while sending a kick, bass, and lead vocal-heavy mix to the drummer’s monitor. What’s important to remember is that the AUX busses are not sent to the Main or Master output, which is what the audience hears, so you can independently control monitor mixers without impacting the sound in the house.
On a MultiMix mixer, if you use both AUX busses for monitoring, the AUX Send B is Post-Fader Level, which means that the channel’s level control impact its level in the AUX B Send, so you will need to adjust to accommodate. That means that if you take the level down in the Main Mix for the lead guitar, you’ll need to increase the level in AUX Send B for that channel so the players on the stage aren’t left wondering where the lead guitar went.
Control Room, Headphone, and Alternate Busses
The Control Room buss is another secondary output apart from the Main Mix that offers extended control over the routing and volume of the different signals. For example, you may have a click track bussed to the monitoring system, but not the main mix. That way the performer can hear the click and lock in time without the audience hearing it.
We hope this has been an educational and informative column on the basics of mixers. To learn more about our MultiMix series, follow any of these links.
MultiMix 4 USB – Four-channel mixer with USB-digital audio interface
MultiMix 6 FX – Six-channel mixer with built-in effects
MultiMix 8 USB – Eight-channel mixer with effects and USB-digital audio interface
MultiMix 8 USB 2.0 – Eight-channel mixer with effects and multi-channel USB output
MultiMix 8 FireWire – Eight-channel mixer with effects and FireWire-digital audio interface
iMultiMix 8 USB – Eight-channel mixer with effects, USB-digital audio interface, and recording and playback for iPod
MultiMix 8 Line – Rack-mount eight-channel stereo mixer
iMultiMix 9R – Rack-mount nine-channel mixer with playback for iPod
MultiMix 12R – Rack-mount 12-cannel mixer
MultiMix 16 USB 2.0 – 16-channel mixer with effects and multi-channel USB output
iMultiMix 16 USB – 16-channel mixer with effects, USB-digital audio interface, and recording and playback for iPod