Gain, Volume, Loudness

Hello Troubadourians! This column is sort of a continuation of last month’s column. I’ve been asked many times about how to get a good tone without being too loud. I often reply with “Who says that you can? And further, who says it’s too loud?” Of course, I’m being snarky, and I realize that neither is very helpful, so I’ll try to be more specific for this column.

What is the difference between gain and volume, and how does each contribute to overall loudness?
Let’s start with what it is that we are amplifying. Whether it is the signal from an instrument pickup or the signal from a microphone, those signals are very weak. From the output of the instrument or microphone, the signal chain is as follows: Preamp, tone controls, power amp, speaker. Gain is mostly associated with the preamp stage and can be thought of as setting the sensitivity, or in other words, how far the amplifier will reach for a signal and how much it increases the signal it receives. Here, the signal is boosted to a level that is considerably stronger and can be controlled and manipulated by subsequent stages. The next stage is the tone controls or equalization (EQ). Technically, tone controls are different from EQ but for the purpose of this column we’re going to use the terms somewhat interchangeably. The raw, boosted signal from the preamp can be sonically altered by adjusting the emphasis of the frequencies contained in the original signal. The power stage is next, and this is where the maximum output—the volume—of the amplification system is determined. In lower power amplifiers, such as small instrument amps, there is often no control over the output from this stage. Instead, overall output is controlled by the output from the preamp. In other amplification systems, these is an output control for this stage, often referred to as a Master Volume, which provides control over the final output level. Finally, there are the speakers. The efficiency and frequency response of the speakers can significantly enhance or detract from the overall output lever—the loudness—as well as the overall tonal character of the amplification system.

How does all that affect loudness?
In the preamp, the ratio of input signal to output signal is the first place where loudness is determined. Whether the ratio is 10:1 or 100:1, for instance, will set the initial potential for how loud the system can be. (The tone stage can also affect overall output, but we’ll discuss that in the next section.) The power amplifier has the greatest control over the loudness as the amount of power—measured in watts—determines the overall potential for how loud the system can get. The speakers are the final stage of the signal path and as stated above, serve to either accentuate or attenuate the amplified signal. It should be noted that speakers are passive and have no potential to add gain to the system.

What effect does EQ have on gain, volume, and loudness?
There are two basic types of EQ: active and passive. Most instrument amplifiers have passive EQ, also called tone controls. They are called passive because they have no gain circuitry, only passive components such as resistors, capacitors, and inductors. They only attenuate a frequency band that is determined by the component values. Turing down passive tone controls both alters the frequency response of the signal that is passed through the circuit and somewhat lowers the overall output of the signal. Turning up passive tone controls allows more of the potential signal to pass through the circuit up to the maximum output level from the preamp stage. Passive tone controls are considered to operate in a subtractive mode.

Mixing consoles, on the other hand, usually have at least some active EQ and can both boost and attenuate (cut) certain frequencies. Again, the frequencies affected by the EQ are determined by the components in the circuit and are usually adjustable to shape the frequency band that they effect. Since active EQ has the ability to boost the signal that is received, they can make the output signal somewhat louder that the signal received from the preamp stage. Care must be exercised when setting the levels of active EQ as the output can sometimes overdrive and distort the following amplification stages. Active EQ can operate in both additive and subtractive mode.

How do we control each one?
Most adjustable controls, whether for gain, volume, tone, or EQ are essentially some form of potentiometers. Potentiometers or pots’are adjustable resistors. Because of their composition, pots are better suited to be constructed to be adjustable than capacitors or inductors. This is ideal for controlling gain and output levels but does somewhat limit the potential for sculpting EQ. Some exotic audiophile-type amplifiers do have adjustability for capacitors and inductors, but the resulting size and fragility of these systems render them impractical for use with musical instruments. Additionally, our ears and taste for tones has been developed over the years by the limitations of the components that are used and anything else often just sounds weird to us. Changing the value of the potentiometer by rotation or linear movement (fader), is the essential way for us to control gain, volume, and EQ. Potentiometers are constructed to have either a linear taper or an audio taper (logarithmic taper), which determines their operation in the circuit. Linear taper changes the resistance in a mathematically linear way which means that most of the change occurs in the final area of rotation. Audio taper changes the resistance in a logarithmic way which follows the way that the human ear perceives changes in sound levels. Normally, an audio taper pot is preferred when directly controlling output volume levels, but a linear pot can be better suited to internally adjusting the performance of a particular stage of amplification that isn’t directly connected to output levels.

Mixing consoles v Instrument amps.
So, what are some differences between mixing consoles and instrument amps? Mixing consoles have a flat response and active EQ. Flat Response refers to the response of the circuit to the audible frequency spectrum. As the word flat would imply, all frequencies are heard by this circuit equally with no frequency or frequencies favored—or colored—over any others. This is important when amplifying highly variable input sources such as human voices, acoustic instruments (including drums and percussion), and other sound sources such as instrument amplifiers. Instrument amps are not flat response, which means that they favor certain frequencies unequally, usually providing some sort of midrange bump, which delivers the characteristic tonality that we have become accustomed to hearing from guitar amps. Historically, this was a limitation of the technology that was available when early guitar amps were designed. Now we expect them to sound that way even though they don’t have to. Most acoustic amps have flat response and active EQ which makes them suitable for reproducing the normal sound of acoustic instruments. Try playing your acoustic guitar through a regular electric guitar amplifier and you’ll see what I mean. Amplifiers designed for bass guitar are closer to having a flat response, but some still have some favored frequencies that are bumped as per many bassists’ preference.

Finally, to best understand what most effects how loud an amplifier is or can be, work backward from the speakers. Speaker efficiency and response will determine whether an amplifier operates to its potential output loudness and can be controlled, or if is ends up sounding like a muffled mess. The wattage of the power amplifier determines the potential output loudness. The EQ sets the frequency curve for the next stage, and the preamp determines the initial gain for the entire system. It is in the understanding of the function of each stage that will provide you with the knowledge to have control over every stage and being able to balance each part of the amplifier or sound system with the others is how you get a good tone. Your ear is your guide. Results may vary…

Need to know? Just ask… Charlie (ask.charlie@hotmail.com)