Gain Staging - Notes from Chuck-at-Bose
OK – Gain, in the context of a highly transparent audio system. To some, the following will seem like long-winded nit picking. If you’re perfectly happy with the sound that you’re producing with your systems, no matter how you’re getting it, then by all means don’t fix what ain’t broken. To others, it may be perceived as overly simplified. Please know that I’m not trying to ‘dumb it down’. I offer this attempt at explaining how audio systems work, in the most non-technical language that I can muster, to anyone who wishes to learn how to coax the absolute best possible results from their audio system. Your critique, the measure of my success/failure, is welcome and appreciated…
Let’s begin at The Source.
Imagine a tiny wave riding down a wire at the speed of light. We know what caused the wave and that it was beautiful. We want to somehow use the tiny wave to move the air around us with sufficient energy and uniformity so that everyone in the space can hear that beautiful source clearly. When we hear the sound clearly, we may smile and leave it alone, or wince and choose to modify some of its traits, but ideally, any gizmos that we use along the way shouldn't impose unwanted changes...
Examples of Sources
Some examples of simple sources:
- Voice > mic > wire >
- Instrument > wire >
- Instrument > mic/pickup > wire >
- Instrument > pickup > wire > mic'd amp > wire >
- Recorded sound > recorded sound player > wire >
Some examples of sources which are more complex:
- Voice > mic > wire > effects/mixer > wire >
- Instrument > mic and/or pickup > wire > effects/mixer > wire >
- Recorded sound > recorded sound player > wire > effects/mixer > wire >
For the past several decades, we humans have strived to make our beautiful sources louder and clearer with the goesintas, comesoutas, amps and speakers of (cue announcer voice) THE SOUND SYSTEM. The mere mention of it strikes fear into the hearts of many, but it can really be quite friendly and effective if we understand how to make a few sensible adjustments to help it perform at its best. To those of us wanting only to produce and control what is heard by us and our audiences, these gizmos are nothing more or less than a series of controlled steps toward making our wave bigger. These steps are commonly referred to as gain stages by tech-head geeks like me. Let's look at the path that our tiny wave follows through an audio system:
- Source – Our tiny wave. Its output connects to a gizmo with knobs and meters on it...
- Trim – First stage of the gizmo. Makes the tiny wave bigger, just the right size for the gizmo to do its best work...
- Level – Second stage of the gizmo. Brings the now bigger wave into balance with others that are sharing the gizmo and to where their mix creates a level that makes the next stage happy...
- Master – Combines all of these bigger waves and sends them to the next stage at a level that makes it happy...
- Power Amp – A last big boost, by far the biggest of all, so big that it can make a loudspeaker wiggle, a lot...
- Loudspeaker – Makes air wiggle, a little or a lot...
- Wiggling Air – Makes people wiggle. (Whole 'nother subject. Back to gain...)
Put it Together
For the simple sources above, we simply plug into an input channel of our favorite gizmo, hit it as hard as we're gonna and then adjust that channel's controls, step by step - first Trim, then Level - for the desired result, optimum performance. Repeat for each additional source. Then we bring up the Master volume control to the desired listening level. Now that we can hear the individual sources clearly, we can modify their tone with EQ, their mix (relative balance) with Level controls and the overall loudness of that mix with the Master, to suit our tastes and needs. Done.
The more complex sources above bring lots of their own gain stages to the party. Our ears hope that we've set them all correctly before we plug them into something that will let us hear them. Failure to optimize each and every one of them can and usually does result in unwanted changes to the source (e.g. hiss, insufficient level, distortion, feedback) which our L1s will very faithfully reproduce as wiggling air. For example, if we run the Master of an external sub mixer well below its output capacity, we're sending a mix that has higher hiss content than necessary to the next stage, the PS1 Input. We end up boosting that next stage to compensate, which boosts the signal, yes, but it also boosts the hiss by the same amount. Hiss is bad. It is unwanted noise. Some noise is inevitable in any gizmo, but since it is part of the sound to which we are critically listening, we want to minimize it wherever possible. We’re going for what tech-head geeks like me call ‘the highest possible signal-to-noise ratio'…
When wiggling air with our beloved half-cylinders, I propose that we'll always get the best possible sound quality when we set each and every stage of an external sub mixer, input through output, for optimum performance (as much signal as possible, but not too much) before connecting it to a PS1 input. Then we optimize the PS1 Input's trim control. Then level. Last of all, we adjust the overall system volume with the Master on the R1...
Hiss without the R1 Remote
Notice that when we fire up a system without an R1 Remote connected, we hear noticeable hiss, even with nothing else connected to the system. This is because we’re running the system as if the Master was set to the 12:00 position, way higher than it needs to be for silence, or even for lower listening levels.
With no R1 Remote and sources connected and producing sound, we find the hiss to be noticeable only during silent passages and at lower listening levels. At louder listening levels, the signal has gone up while the hiss has stayed the same, so the hiss gets covered up, or masked by the louder signal.
The best and only way to minimize/eliminate the hiss during silence or lower listening levels is to optimize every stage before the R1 Remote Master and then use the R1 Remote Master to achieve the desired listening level. Using the system without the R1 Remote means that we’re stuck with any hiss that the system produces when that last stage stays set so high. It can also mean that we’re not allowing access to all of the available volume, since 12:00 is only half-way up the dial. If we’re always listening at a louder volume levels, never distracted by hiss and we don’t ever find ourselves wishing that we had a tad more volume, then we may certainly forgo the R1 Remote Remote…
Full Power at 12:00 on Master Level
Even without the R1 Remote control the system can get to full output if the input trims are carefully set.
If you do proper gain staging, the system will get to full output with all knobs at 12 o'clock. Since proper gain staging is not trivial, we provide the extra gain to take up the slack if the input is not quite hot enough.
- Hilmar-at-Bose quote from the discussion board