Understanding gain structure and signal flow is a key factor in successfully setting up and operating any sound system. This is true, from your car or home stereo, to a sound system in a theater, arena, or stadium. The basic principles of audio and acoustics, just as they are based on physics and electricity, are true across the spectrum of scale, for possible configurations.
Your source can range from an acoustic piano, to a dj mixer, to a car cd player. Your source either has an acoustic and/or digital output, that can be categorized as instrument level, mic level or line level. Acoustic instruments or extensions of them will most of the time be categorized as mic level, ie. mic’ing an acoustic guitar or vocal, or the output of an electric guitar amp. But these designations can change, ie. an acoustic guitar has a pickup and a 1/4″ instrument level output, that can be plugged into a D.I. box run into the system at mic or line level.
At the console, all of your input sources now converge, into what is in essence a matrix mixer, ie. many, input sources, that can be manipulated and routed to multiple outputs simultaneously. Each input channel will contain some combination of pre-amp, eq, aux sends, fader, mute switch, etc. The first gain stage your signal will come to will be your pre-amp. This is where your source output gain arguably matters most. Besides output level of electronic instruments, mic positioning, D.I. pad features, etc., the signal reaching the pre-amp is the first check of your signal to noise ratio.
In any audio capturing situation, be it acoustically, or electronically, the goal is to capture as much amplitude, (the volume of gain), as possible without clipping or distortion, to achieve the balance of your signal’s dynamic range in relation to headroom and signal to noise ratio. Headroom is the space between top of your signal’s amplitude and clipping. This becomes increasingly tricky with instruments with large dynamic ranges, such as a trap drum kit. If you have listened to records and/or cassette tapes, you will more easily observe a slight hiss, low level hum, or just a general low level noise, like white noise. In the analog or digital realm, if you turn up the gain very high on a source, you will also start to hear this same type of noise. This is referred to as your noise floor, the ambient noise being amplified by your transducer.
Gain structure is the optimal setup of gain stages, in order to achieve maximum signal to noise ratio. In other words, as much direct signal of your source, compared to the noise floor. If you place a microphone 6 ft. away from a source, you will hear much more acoustic reflections in comparison to the direct sound coming from the source, than if the microphone was only 1ft. away. The same also goes from a digital source. In any scenario, raising the pre-amp level on a console input channel, will also raise your noise floor along with your source’s direct signal. The less optimal your gain structure, the more noisy your input signal. For instance, if the output of a DJ mixer is too low, going into the input of an audio console and you have to raise the pre-amp level a considerable amount, your signal’s sound may appear to be distant, lack definition, and sound like you are playing a poorly recorded track. On the other hand, too much source signal can be undesirable as well, causing clipping and/or distortion because of the lack of headroom in your dynamic range.
The biggest thing to remember, is that achieving optimal gain structure and signal to noise ratio, is about maintaining an even balance, from your source signal, to the outputs of your speakers.
“All of our posts are put together by the staff at JR Sound Co. a small outfit from Las Vegas, NV. For more on us, visit our website at www.jrsoundcompany.com, cheers! ”