Audio Volume Controls and Perfection – Why Not?

Last week I came across a fanciful article on volume control interface design, and while this article was done in jest, it got me thinking about the basic problem – making a perfect volume level adjustment device, be it a preamplifier with gain or a passive control. Currently, you can get lots of options for good, but no option for perfect…let me explain further…

First how do we define perfection?  For my purposes it would be a volume adjustment that possess both infinitely continuous and contiguous level adjustment options while remaining completely transparent at all volume levels.

And why, after all these years of audio technological development, doesn’t such a device exist? Let’s see…

Why do I demand a continuously variable volume control? Because when I compare the analog outputs of two source devices or the output levels of two different loudspeaker systems, I want to be able to match them as closely as possible. If a volume control has .5 dB incremental steps but the differences between two outputs is .2 dB Matching them will be much more difficult (if possible) than if the volume control was a continuous uninterrupted scale.

So why not make all volume controls continuous rather than stepped? The answer here is that you can get more accurate and more reliable and more long-lasting results from a stepped volume control that uses a resistor network than from a volume control with a resistive brush or potentiometer controls.

So, for matching levels critically, you need a continuously variable volume control, while for the best sound quality you need a stepped, matched resistor volume adjustments. Why not just make a volume control with .1 dB adjustments? Because it would be expensive, and if not driven by a sophisticated and fairly powerful motor system it could also be slow. And even then, .1 dB might not be a fine enough adjustment for some comparisons and testing (yes, I know that some articles and experts state that a .2 dB is the smallest difference we can readily perceive).

Obviously, if you never compare components or do any A/B testing, a stepped volume adjustment is very likely your highest quality option. But if you do compare components be aware that the stepped volume control may not be capable of delivering a true level playing field for sonic comparisons.

I’m old, I know that, but I’m still waiting for the perfect volume control…