Would you be surprised to learn that there is a real difference between volume controls and level controls? Unfortunately today, controls which are really “level” controls routinely get tagged with the label “Volume”. But what’s the difference?
How We Got Here
In the early days of hi-fi audio there really was no confusion. Most systems that played music were self contained. There was one control labeled volume and if you wanted the music louder or softer you adjusted that control. Then things got complicated.
In the 1960s systems got divided into sources (turntable, tape deck, receiver, etc.) and amplifiers. This was the beginning of the confusion because it introduced the concept of the “line level” signal to the general public. This was a topic previously reserved mostly for audio technicians with the proper training and experience to understand what it meant. But it wasn’t too bad because, in most cases, the sources lacked any type of level adjustment and there was still just a “volume” control on the final amplifier. Sources were (for the most part) standardized and things worked out fairly well. Then a terrible thing happened… the introduction of the separate “preamp” and “amplifier”. This is when the confusion really took off.
Suddenly systems got build around a “preamp”. These preamps were integrated units with source selection, level controls, tone controls, integrated phono RIAA preamps, level indicators, headphone amplifiers, and all manner of other controls. But in operation these preamps were required to interface with a large number of different sources and amplifiers. And this again returns us to the “line level” signal. Because the sources generally all put out a defined “line level” signal and the preamplifiers supplied a line level output to the amplifiers things should have worked out fine. But it didn’t. It started with several competing specifications for what constituted “line level” and some deliberately confusing marketing by several audio companies.
Soon it was common for different sources to put out wildly different “line level” signals. Differences as great as 10dB became common. So the preamp manufacturers added dedicated level controls and indicators to the preamps. Not to change the volume or Sound Pressure Level of the music, but to ensure that the output of the preamp going to the amplifier was at an acceptable level to prevent overdrive. But unfortunately many of those controls eventually got labeled as “volume” instead of “level”. At the same time, some standalone amplifier manufacturers began adding the labeling “Master Volume” to their amplifiers which only added to the confusion.
Now we come to today where the situation is hopelessly muddled. Not only do we have all the traditional sources available, but streamers, computers, A/Ds, Bluetooth receivers, smart TVs, and all manner of software controlled devices. And all of these seem to contain an actual or virtual control labeled “volume”.
And to further complicate matters we also have sources mastered at wildly different levels. A classic CD mastered in 1990 and the same CD “remastered” in 2010 can have vastly different levels of overall output, compression, and sometimes a complete remix. The same is true of vinyl. So how do we sort it all out.
The Solution
The answer to untangling this Gordian Knot is the same one Alexander The Great used. We must cut it asunder.
This is actually much easier to do that you might think. Instead of arguing about system topologies or amplifier characteristics, the key is to go back to the simple concept of the “line level” signal. Regardless of topology we must understand that the ONLY part of the system which should be affecting “Volume” (or more directly Sound Pressure Level or SPL) is the final amplifier and speakers. Every other interface is a signal interface.
What this means is that instead of thinking of all these different system components as having a volume, they really each have a level control. And the purpose of that control is only to ensure that the output of that device meets an accepted “line level” standard. In theory, the line level input fed to the final amplifier should be sufficient to drive the amplifier to full power. This is why input sensitivity is specified for amplifiers. And this is why there is really only ONE PLACE for a volume control; on the final amplifier. Every other level control should be tailored to ensure that components are all fed by appropriate line level signals.
Does It Really Matter
Now I can already hear the arguments coming at me from across the internet. But this subject matters for two very distinct reasons: Signal-to-Noise and Overdrive.
Starting with signal-to-noise or SNR, this has huge effects on the overall sound and performance of your system. Each stage of the system from the source to the amplifier has its own minimum noise floor. Each stage will produce this amount of noise regardless of the input or output. By reducing the level of any particular stage in an attempt to control system volume, what is being reduced is signal (or the music) and not the noise. This means that by reducing the output level below the line level expected by the next stage, it decreases the signal to noise ratio of that stage. And because each stage except the amplifier has basically unity gain (line level in and line level out) the decreased SNR or increased noise figure affects the entire system. By adjusting each stage level so that it produces essentially a line level output, the overall SNR of the system is maximized and the noise is minimized. It also means that there is never any reason to adjust the “level” controls unless the system is reconfigured (including selecting a different source).
The second reason is Overdrive. This can be an inadvertent condition with can seriously degrade your system performance even at low overall volumes. If you have a source (like a streamer) and the level is set too high, it’s output can exceed line level. Then the next stage (for example, a preamp), which is expecting a line level input, gets over driven and distortion occurs, But if the next stage (like an amplifier) is set to lower volume, it is not over driven but it still amplifies the distortion created in the preamp due to the excessive drive level coming out of the streamer. So the overall system has added distortion and the source of that distortion is not immediately evident.
The solution to both these issues should be evident. Each of these problems is avoided if only line level signals are ued to connect each stage of your system. If you characterize each component or source and set each level control so that the signal levels between stages are ALWAYS line level, the both problems are avoided. And it leaves the system properly configured and with one, and only one, volume control.
The Process
So the process is simple to describe, but less simple to implement. In theory all that’s required is to adjust all level controls to get appropriate line level signals between stages. But that generally means having a method to characterize to outputs of each stage. For this I use a set of meters like the Purpleheart Signal Meters. By inserting the meters after each source and stage, it’s easy to characterize and set levels. This is also the reason for the signal meters on the Source Selector Preamp. In this unit, the signal meters are on the output but the level control is on the input. Because the overall mid level gain is approximately unity, I know that setting the level control until the meters read appropriately I am not over driving either the preamp itself OR the amplifier connected to the output. And by setting the level control to mid gain, I know what the level of the source feeding that channel of the preamp is set to.
Once this system balancing is completed, it is a simple matter to use the amplifier volume control to adjust the volume or SPL. And if the source is changed to a different box with a different output level the preamp level control can be adjusted until the meters again register an appropriate line level. It also means that in a properly adjust system, there are not big shifts in overall volume when changing sources. I can switch from receiver, to CD player, to computer and the volume remains remarkably constant.
Conclusion
Some readers may think I am just being overly pedantic. But these issues are real. And in the DIY community, where builders are constantly changing equipment and experimenting, they crop up with amazing regularity. On many occasions I have been asked to diagnose an amplifier distortion problem only to discover that the real issue was improper signal levels within the system. Once the signal levels get corrected, the issues go away.
So that’s my Old Man Rant for the day. Let me know what you think or how you deal with signal levels within your systems.
As always, questions and comments are welcome.