Posts Tagged 'flow'

Components of a Pro Audio System

A SIMPLE, GENERIC SYSTEM LAYOUT

In this lesson, we will begin looking at the different components of a professional audio system. In articles to come, we will look in more detail at each component separately.

Source. This would include microphones, direct boxes, playback & other sources of audio.

Mixing Console. Where most of the action happens – the blending of inputs and outputs.

Processing. Various components which tweak and split the sound for various uses. Functions in a system processor would include Crossover, Gain, Polarity, Equalization, Delay, Merging & Splitting.

Amplifiers. Equipment that receives line-level inputs and delivers speaker-level outputs.

Loudspeakers. The various forms of transducers that convert electrical signal into acoustical energy. They are manufactured to optimally project a specific frequency range, i.e.: subwoofers, woofers, mids, and high-frequency horns.

SYSTEM FLOW TERMINOLOGY
It is important to get into the habit of speaking in terms of proper signal flow. Often, you will hear someone say “my amp is plugged into my guitar”. This is not correct. The guitar is the source. The sound travels O U T of the guitar, down the path of the cable, and I N to the guitar amp’s input. This same thinking applies to every input and output in an audio system. Force yourself so use the correct terminology, bearing in mind the direction of signal flow. You don’t plug anything INTO the output of a mixer! The mixer’s output plugs INTO the next piece of gear in the chain.

THE IMPORTANCE OF GAIN STRUCTURE
In a properly set up system, the console, processing, and amplifier inputs should all clip (reach the point of distortion, or overloaded signal) simultaneously. This gives you tha maximum headroom  (also called signal-to-noise ratio) out of the entire system chain.

THE AGE OF DIGITAL
Just a few years ago, the “processing” component of the signal chain was an entire rack or two of different pieces of gear. But in today’s reality of excellent quality digital audio processing, that same amount of processing (and more) fits in just 1 or 2 rack spaces. In addition, the proliferation of digital mixers and self-powered speakers means a lot of today’s signal chains look quite a bit different than those of just 15 years ago.

Understanding Signal Flow

Knowing the audio path through a mixing console is absolutely critical to a sound engineer’s success. Using this information, the engineer can quickly TROUBLESHOOT the likely causes of common problems, and can even narrow down the possibilities of unexpected major problems. It can also prevent mistakes because you know what the audio is doing at each stage of the console.

It also gives the audio tech CONFIDENCE as he sits behind the console. This is because he fully knows the ins and outs (sorry for the pun) of the equipment. Finally, it gives the audio tech a FOUNDATION of understanding which allows them to move from room to room or console to console and not be thrown for a loop. Instead of thinking, “the 2nd red knob on my old console was always set to 12:00, does that mean the 2nd blue knob on this console should be set the same?” The knowledgeable tech will know exactly what that knob is and where it is in the audio signal chain (even consulting the owner’s manual if necessary.)

You want to be an excellent all-around driver of vehicles, not a specialist who only knows and drives a Chevy Malibu 2-door with the small V6.

GENERALITIES:
In general, the controls that you tend to “set” are at the top of the console, meaning you have to actually reach for them. The conrols that need more adjustments along the way are closer to your hands (i.e.: the channel faders.)

The channel strip tends to lay out generally “in order” as it applies to the audio signal flow – Gain, then EQ, then the Fader, for example. But this is a very broad overview. There is much more detail to be learned.

So how do you learn the signal flow of your paticular console? You break out the manual. It will contain what is typically called a “block diagram”. Now block diagrams can be headache-inducing nightmares. Check out this one for a Yamaha DM2000:

So I recommend that you take the time to create your own simplified signal flow. Just follow the lines on the block diagram to determine the signal path. It’s also recommended that you make it in linear, vertical orientation so that it helps you visualize the flow better. You can use any drawing or paint program to make one.

EXAMPLES:
I have created a few Signal Flows for study. They can be extremely valuable learning tools. (Click on the images to see a full sized version). [Note: These images are for personal study only. Not to be used in any other websites or printed materials.]

Here is the signal flow of a Mackie 1604 VLZ.

And here is a larger format Yamaha IM8•40 console.

And here is an APB Dynasonics Spectra-C/56

BASIC DEFINITIONS:

Gain: A level adjustment designed to optimize each signal coming into the console.

Pad: If you turn the gain all the way to the left and the signal is still too hot, then you should engage the pad, which will reduce the incoming signal by a preset amount (usually 20 dB or so).

HPF: High-Pass Filter. A circuit which sharply decreases low frequencies, reducing mike handling noise, stage rumble, and plosives (p-pops).

Polarity: A simple switch which flips the polarity of the input. (Sometimes incorrectly labeled ‘phase’). Useful for eliminating phase-cancellation when using multiple mics on the same source (both the top and bottom of a snare drum, for example).

Insert Loop: A patch point for connecting outboard gear, such as a compressor or effects unit.

Direct Out: An individual channel output after the gain stage, but before EQ or fader involvement. Most often used for feeding multitrack recorders.

Aux mix: A separate mix of each channel which has its own output, which can be used to feed stage monitors, a recording mix, sends to a reverb unit, or other uses.

Pre/Post: An indication of where the Aux mix splits off from the main signal. If it is labeled as as “Pre” or “PreFade” mix, then its level is completely independent of the channel’s fader. If it is labeled as a “Post” or “PostFade” mix, then the aux’s level will also be affected by the channel fader as it is adjusted.

PFL: Pre Fade Listen. Works as a “solo” button for the engineer’s headphones. You can isolate an individual channel, and hear changes you make with the EQ. Because it is pre-fade, it does not matter where the fader is at the time.

Group/Subgroup: A Subgroup (or just “Group” on some consoles), is a tool used to help the audio tech during a service or performance. Rather than have to independently mix 32, 40, or even up to 56 channels on a console, you can assign for example, all the drums to one fader called a “subgroup”. The Subgroup does not affect any aux sends, it only affects the main mix. So I can raise or lower the level of all 8 drum mics on one fader – VERY USEFUL.

VCAs and VCA Groups: A VCA stands for Voltage Controlled Amplifier and is a common way to “automate” certain things on a mixing console. You can assign multiple channels to a VCA (just like a group), but the difference is – NO AUDIO IS PASSED THROUGH A VCA. Instead, the VCA acts exactly like a remote control to channels which are assigned to it. Where it gets really interesting is that channels that are assigned to a VCA Group DO NOT have to share a common audio path AT ALL. (This means you can have the entire band on one VCA fader, even if they all are routed to different mixes and subgroups!)

Something to keep in mind with VCAs that you don’t have to worry about with Groups: a VCA provides the exact same function as adjusting a channel’s fader (including any changes to it’s Post Aux mixes). This is different than a SubGroup, as a sub would only affect the house mix.

Buss: a common term seen in mixing console owner’s manuals. It is an electrical term rather than an audio term. Technically, an aux mix, a subgroup, a master mix, a mono output, a matrix output, etc. are all busses. The only way this term becomes important to an audio tech is in the possibility that you get some “buss distortion) which may not show up on the meters. If, for example, I assign all 32 channels of a console to SubGroup 1, and the console I’m driving doesn’t have Group Meters, and I keep the Group 1 fader low enough that I don’t get overloads on the Master Mix Meters, then it would be possible to overload the Group 1 buss, creating distortion, that would not show up on any meters. This is an extreme example to make a point – but I think you get it.

Matrix Mix: A completely different kind of output available only on the larger consoles. It’s sole purpose os to create an alternate mix to be used for recording, for routing a different mix to a different room, or for any other specialized purpose. You will not see a Matrix split on the following audio signal flows. Why? Because they are not made up of individual channels! A Matrix mix is created solely from mixing the Main Outputs and SubGroup Outputs. So a Matrix Out is created downstream from any individual channel functions.


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Audio Training for Live Sound. All content ©2010 Jeremy Carter Consulting.

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