Signals 002

I recently measured a capacitor and the instrument told me it had negative inductance. That would be quite a component. Of course, the capacitor had not found a way around the laws of physics. The number on the display was real. But what it appeared to say was not what it actually meant.
This is one of the interesting things about measurement. We tend to think of measuring as a way of replacing uncertainty with facts, and in a very useful sense that is exactly what it does. If a 2.5 mH inductor measures closer to 2 mH, that is something worth knowing. But measurements always happen under particular conditions, and the number we see is often the result of much more than the property named on the display.
A capacitor is a good example. Change the measurement frequency and the indicated capacitance may change. Measure its impedance and the result contains more than capacitance alone. Resistance, inductance, dielectric losses and the physical construction of the component are all part of what the instrument sees. It then has to interpret that behaviour according to the measurement mode and model being used. Most of the time the result is straightforward. Sometimes it is not. The mistake would be to conclude that the measurement is therefore useless. Quite the opposite. Unexpected measurements are often the interesting ones because they force us to ask what we are actually measuring.
That question matters in audio. We measure distortion, frequency response, noise, impedance, phase, capacitance, inductance and dozens of other things, with a precision that would have been extraordinary not very long ago. But precision and meaning are not the same thing. A distortion figure tells us something about distortion under the conditions in which it was measured; it does not describe an amplifier. An ESR figure tells us something useful about a capacitor; it does not tell us whether it is a good capacitor for a particular circuit. A frequency response can reveal a great deal about a loudspeaker, but it is not the loudspeaker.
None of this makes measurement less important. For me, it makes measurement more interesting. The purpose is not to collect numbers that confirm what we already think, but to understand what is happening. Sometimes that means measuring again at another frequency, changing the test setup or looking at a circuit rather than a component in isolation. And sometimes it means accepting that the number on the display was perfectly valid, but the first conclusion we drew from it was not.
This is also why measurement and listening have never seemed like opposing approaches to me. They answer different questions and, more importantly, they can lead back to each other. Listening can tell me that something changed, while measurement can help me understand why. Measurement can reveal a problem I did not hear, while listening can make me investigate something I had not thought to measure. Neither needs to invalidate the other.
The useful part is the movement between the two. A good measurement does not necessarily end a question simply because there is a number on the display. Sometimes that is where the question begins.
Measurement is one of the most useful tools we have. But the instrument does not know what we wanted to know. That part is still our job.