Sound Engineering LESSON:The Front-of-House Mixer Pt. 2
LESSON: The Front-of-House Mixer• If two signals are electronically out of phase, their waveforms are mirror images of each other. The crest of one wave happens simultaneously with the identical trough of the other wave. When this happens, there is phase cancellation—in other words, no signal. If two waveforms are in phase, they crest and trough together. This results in a doubling of the amount of energy from that waveform, or twice the amount of air being moved.
LESSON: The Front-of-House Mixer• When phase problems occur, the are typically a result of two basic scenarios: 1. An incorrectly wired microphone or balanced line cable. 2. Multiple microphones in the same acoustic space, spaced so that undesirable phase interactions occur as the same sound arrives at the different mics in destructive phase relations.
LESSON: The Front-of-House Mixer• The nature of combining sounds dictates that there is always phase interaction.• Good phase interaction gives our music depth and richness. However, we do want to be particularly aware of phase interactions that can have an adverse effect on the quality of our music.• If your mixer has a phase switch on each channel, it’s probably at the top of the channel near the preamp and attenuator controls. Its purpose is to help compensate for phase interaction problems.
LESSON: The Front-of-House Mixer• It’s a good idea to check for phase problems when setting up your mix. In any situation in which multiple mics are used in close proximity, be on alert for a hollow or thin sound. This is different from a sound that simply has a reduced frequency content in the low frequencies—it literally has a hollow and thin sound. When you recognize this sound, look at the microphones and how they are set up and aimed. Any mics that are pointe at each other, on- or off axis, could be causing the problem. One at a time, invert the phase on those mics. There’s a good chance that you’ll hear the sound solidify and fill out.
LESSON: The Front-of-House Mixer• Condenser microphones and active direct boxes need power to operate. If they don’t receive it, they won’t work. This power can come from a battery in the unit or from the phantom power supply located within the mixer.• Phantom power (a very low amperage 48-volt DC current) is available at any mic input that has a phantom power switch. Because amperage is the actual punch begin the voltage and because phantom power has a very low amperage, there’s little danger that this power will cause you any physical harm, even though the power ravels to the mic or direct box through the same mic cable that the musical signal travels to the mixer.
LESSON: The Front-of-House Mixer• The effective output of each microphone is typically quantified in relation to line level. Most microphones output a signal that is between 30 and 60 dB below line level. This means that the signal from the microphone must be boosted between 30 and 60 dB before the signal strength is at line level and ready to move through the mixer.
LESSON: The Front-of-House Mixer• Line in and line out are common terms typically associated with mixer, outboard equipment, and tape recorder inputs and outputs. The signal that comes from a microphone has a strength that’s called mic level, and a mixer needs to have that signal amplified to what is called line level. The amplifier that brings the mci level up to line level is called the mic level, and a mixer needs to have that signal amplified to what is called line level. The amplifier that brings the mic level up to line level is called the mic preamp.• Instrument inputs on mixers are line level. An input that is line level enters the board after the microphone preamp and is, therefore, not affected by its adjustment.
LESSON:The Front-of-House Mixer
LESSON: The Front-of-House Mixer• Most modern mixers have what is called a channel insert. This is the point where a piece of outboard signal processing can be plugged into the signal path on each individual channel. If your mixer has inserts, they’re probably directly above or below the microphone inputs.
LESSON: The Front-of-House Mixer• A channel insert lets you access only one channel at a time and is used to include a signal processor in the signal path of that specific channel. The processor becomes a permanent part of the signal path from that point on; therefore, its level affects the remainder of the signal path. Inserts are especially useful when you are using a compressor, gate, or other dynamic processor.
LESSON: The Front-of-House Mixer*The insert effect is bypassed when no insert is present.
LESSON: The Front-of-House Mixer• An effects bus (such as aux 1 or aux 2) lets you send a mix from the bus to an effect (typically outside the mixer, but often simply routed internally to an effect, headphones, and so on), leaving the master mix on the input faders without effects. The output of the effect is then plugged into the effects returns or open channels on the mixer. This is good for reverbs and multi-effects processors.
LESSON: The Front-of-House Mixer• The term bus is confusing to many, but the basic concept of a bus is simple—and very important to understand. A bus usually refers to a row of faders or knobs.• If you think about a city bus, you know that it has a point of origin (one bus depot) and a destination (another depot). Depot 1 Depot 2
LESSON: The Front-of-House Mixer• You know that the bus picks up passengers and delivers them to their destination. That’s exactly what a bus on a mixer does.• For example, in concert the fader bus has a point of origin (the instruments and voices on stage) and a destination (the amplification system). Its passengers are the different ingredients of the mix. Not all channels (passengers) necessarily get on the bus, but whoever rides goes to the same destination. Depot 1 Depot 2
LESSON: The Front-of-House Mixer• Mixers also have auxiliary buses or effects buses. Aux buses (also called cue sends, effects sends, or monitor sends) operate in the same way as the fader bus. An aux bus (another complete set of knobs or faders) receives its signal from the channel inputs. There is typically a switch that lets the sound operator choose whether the signal originates toward the beginning of the signal path (Pre Fader Listen) or near the end of the signal path (After Fader Listen). It picks up its own set of the available passengers (channels) and takes them to their own destination (usually an effects unit or the monitor system). Pre Fader Listen
LESSON: The Front-of-House Mixer Input Faders• When everything is set properly at the preamp, use the input faders to set the channel mix levels. Mixing live sound is different than recording. In a live mix, the main channel faders are used to set the mix volumes for each channel, whereas in a recording session, these faders might be used during tracking to set the recording level, with another knob or fader controlling the actual mix.
LESSON: The Front-of-House Mixer Pre and Post• Aux buses often include a switch that chooses whether each individual point in the bus hears the signal before it gets to the EQ and fader (indicated by the word Pre) or after the EQ and fader (indicated by the word Post).• Selecting Pre lets you set up a mix that’s totally separate from the input faders and EQ. This is good for headphone sends. Once the headphone mix is good for the musicians, it’s best to leave it set. You don’t want changes you make for your listening purposes to change the musicians’ mix in the phones.
LESSON: The Front-of-House Mixer Pre and Post• Selecting Post is good for effects sends. A bus used for reverb sends works best when the send to the reverb decreases as the instrument or voice fader is turned down. Post sends are perfect for this application because the send is after the fader. As the fader is decreased, so it’s the send to the reverb, maintaining a constant balance between the dry and affected sounds. If a Pre send is used for reverb, the channel fader can be off, but the send to the reverb is still on. When your channel fader is down, the reverb return can still be heard loud and clear.
Sound Engineering LESSON:The Front-of-House Mixer Pt. 1