Don’t Fear the Gear, Part 1: Signal Flow
The first step to sound-system mastery is understanding the basics of input and output.
The ways of the sound system often seem mysterious. What do all those knobs do, anyway? Why does it sound great one day and terrible the next? Most group fitness instructors are simply content to find the “on” switch. Yet we all know that an audio breakdown is frustrating (and embarrassing), not only to us, but to our participants.
Faced with technical difficulties, it’s common to become paralyzed by “gear fear,” but you may have the power to fix the problem! First you must know where to look. Understanding basic signal flow is essential to troubleshooting an audio system malfunction.
Signal Flow Basics
Signal flow is the path an audio signal takes from source to output, including all the processing involved in generating audible sound from electronic impulses or recorded media (Roback 2004). In other words, the sound of your voice going into the microphone (source) must eventually make it through the entire system before making its way out of the speakers in the form of amplified sound. Other sources include an MP3, CD or DVD player, a microphone, a video game console, etc. If you have something you wish to hear at an amplified volume or see on a larger screen, it’s most likely a source. For most classes you’ll need at least two sources: music and a microphone.
Pots, Faders and Cables, Oh My!
Let’s take a look at a professional yet basic audio system. To determine the signal flow, it is useful to know about inputs and outputs. Imagine the signal as air traffic. If a piece of gear represents an airport, then the signal is either an inbound or an outbound “flight.” Similarly, the signal flows into a piece of gear through the inputs and out of that particular piece of gear through the outputs. Signal traffic can only go one way. Although you may never be personally responsible for setting up your club’s audio system, knowing how the signal flows through each component will arm you with the knowledge required for basic troubleshooting.
Cables. First of all, where do signals from a CD player go and how do they eventually make it to the speakers? Low-voltage electricity moves from the inputs through all of the other gear by way of various cables. These cables serve as conduits for the electrical signal that represents your voice, music or instrument. All cables have male or female ends. Although it sounds semi-crude, these titles do make it really simple to remember which end is which! See Figure 1 for examples of cables you may encounter.
CD/MP3 Player. Something needs to play the music! CD players are still the norm, but newer systems often have an iPod dock. Beware! If your digital media device is a different brand, this proprietary connection will not work. However, an inexpensive one-eighth-inch stereo cable (see Figure 1) is all you need to plug in any MP3 player to your current system. There are different types of connections available for the other end of the cable, so be sure to check the compatibility with your system.
Microphone. Since the music will be amplified, you’ll need to be amplified as well. Many facilities now provide wireless microphones. “Wireless” refers to the fact that the microphone does not have to be tethered to the system in order to function. A wireless microphone requires three separate components to work properly:
1. Headset microphones are the most familiar to instructors. A small, covered membrane at the speaking end of the microphone vibrates when exposed to sound and converts the sound into electricity. The signal then moves to the transmitter.
2. The transmitter may be attached to the headset or worn in a belt pack attached to the microphone headset with a thin wire. The transmitter works by broadcasting the signal, this time using various radio frequencies. It works similarly to a two-way radio; hence the need for antennae on the transmitter and the receiver.
3. The receiver is the base unit that “lives” with the rest of your system. It literally receives the signal sent by the transmitter and passes it to the next piece of gear in the chain, usually the mixer.
Mixer. The mixer controls many attributes of the signal arriving from each input—including volume. Although individual sources often have their own volume controls, you should leave them untouched and make all volume adjustments from the mixer. Of all the gear mentioned, the mixer can be the most intimidating. When a technical difficulty arises, it is often the mixer that gets adjusted unnecessarily. Jeremy Ruff, audio engineer at GrandVista Music in Nashville, Tennessee, explains: “In an environment with dynamic volume levels, such as a fitness studio, an individual inexperienced with audio can quickly get into trouble simply by adjusting the microphone volume too high. This can lead to further unnecessary adjustments on the mixer–akin to an audio Rubik’s Cube®! I have gone on numerous service calls for just this reason.”
Not to worry. Here’s a secret for stress-free operation. Most traditional mixers are arranged vertically in groups known as channels. If you know what one channel does, then you can easily understand the remaining channels—they’re all the same! Each channel contains all the controls for one specific input. The long red vertical rectangle on the left in Figure 2 is surrounding channel 1 of this Mackie® 16-channel mixer. By plugging a cable from the CD player into the channel 1 input, you can now control the CD player’s sound via this entire column of controls. Channel 2 could be for the microphone, channel 3 for the MP3 player and so on.
The small square toward the bottom of that long rectangle is the channel 1 mute button. If this button is depressed (assuming this channel is for our CD player), the music will not be heard. Why? Because this system we’ve built with components and cables is creating an electrical circuit. If the circuit is “broken” or opened, the signal cannot pass. This is how most light switches operate; a light in the “off” position means the circuit has been broken. The same applies to the mute switch; in the “off” position, the sound has been muted.
The channel 1 volume fader increases or decreases the volume of only the input plugged into channel 1. In this example, it would alter the volume of the CD player only. If you wanted to adjust the volume of all your inputs simultaneously, you would use the master fader volume on the far right. As you can see, there are many other knobs (formally known as potentiometers or “pots”) and adjustment capabilities within this mixer. However, it’s best not to touch these knobs. They were most likely set by an audio professional and are best left alone. Audio system manufacturers have realized that these types of mixers are sometimes too complicated for the group exercise setting, and companies now offer simple 5-channel mixers with only the essential controls. This eliminates the urge to turn every knob and press every button until something works, and it also cuts down on costly service calls.
A mixer also combines all of the source signals into two signals—a “right” and a “left.” This is called a stereo signal. The right and left main outputs connect the mixer to the amplifier.
Amplifier. The amplifier (amp) is usually the heaviest component of an audio system, and so for safety it is often placed at the bottom of the rack. It has its own power switch and volume controls. The amplifier takes the signal from the mixer, makes it louder and sends it to the speakers via cables.
Speakers. The speakers work in the opposite way to the microphone—by taking electricity and turning it back into sound, which is now amplified with any other adjustments made by the gear. Finally! Thanks to the speakers, your voice and music can now be heard at a volume sufficient for a large space filled with people. Remember that while a loud class can be a lot of fun, you have a responsibility to keep your participants safe at all times, and this includes protecting their auditory health.
Our basic system has been designed and the signal now has a way to get from the source to the speakers. So where’s the sound? In fact, where are the familiar glowing system lights? As it turns out, all these fun electronics need electricity to function (duh)!
Power Conditioner. The power your club receives from the power company, generator or other source is not always a perfect 120 volts. Fluctuations in power and inconsistencies in its quality can negatively impact audio systems. Similar to a power strip or a surge protector, the robust power conditioner not only withstands power surges big and small but also ensures that the power supply is even and has been conditioned specifically for the components that plug directly into this device. The power conditioner offers the added bonus of allowing you to flip one switch to turn on your entire system.
Be in the Flow
Armed with the knowledge of basic signal flow, you now have a greater understanding of how every sound system operates! This can come in handy should the inevitable “technical difficulty” arise. Speaking of difficulties, in our next installment we will learn how to F.I.N.D. and eliminate common problems. By understanding the difference between feedback, interference, oise and distortion, you will quickly be able to diagnose and fix any problem like a pro! Remember, have no fear—it’s only gear!
Roback, Steven. 2004. Pro Tools 6 for Macintosh and Windows (2nd ed.). Berkeley, CA: Peachpit Press.