Originally Posted by raddle
Ah, but audio system are dynamic and we do consider their future behavior. When we measure an audio device, we have a way to try to predict its future response to a given input signal. Our measurement may be more or less useful depending on what this future signal is. The signal running through an audio device is always changing while that device is playing music. The hardware doesn't change, but activity of the hardware changes, and that's what we are trying to predict.
I see things differently. By the time we've measured let's say FR it's already "outdated" and if you insist on it being a "model" then such a measurement really would be just a descriptive model of what happened in the past. Since, for all intents and purposes and to make things simpler, audio devices do not change the past observation is still valid now and in the future.
If you compare this to gravity, then measurements would be the speed of an object or distance it traveled since it was dropped at different points in time. That's no predictive model. The model would be formulas such as h(t) = h0 - 1/2*g*t^2.
A model that can really predict the output for any input signal would be, for example, a guitar amp model - a complex mathematical model that takes any input signal and transforms it into a distorted output signal. The better the model, the closer the output will be to the real thing.
You're taking a narrow view here, in answering the question "What is it useful for?" You say you can see signs of instability; I could then ask "What use is seeing signs of instability?" "What use is knowing whether a DAC is oversampling?" Think more generally: what is the purpose of an audio system?
I just gave you practical examples, no superficial babble. If the amp is unstable then you should return it. Now you could continue asking "what is the use of returning an unstable amp?" and I'd answer "because I don't want a broken piece of crap that might harm my speakers/headphones" and so on.
The purpose (as in the target) is faithful reconstruction. Roll-off, instability, bad filters, non-oversampling, funky FR etc. are all signs of failing to meet objective high fidelity reproduction criteria.
If a measurement predicts nothing, then it's a useless measurement.
Disagree. Measuring my weight doesn't predict anything. Measuring my height doesn't predict anything. But combining both can tell me roughly if I'm healthy, too thin or too fat.
But your comment about the basshead is the first time you've referred to how a system is perceived, which is the real key and real purpose of an audio system.
Obviously an audio rig reproduces music for us to perceive it. But that's a bit like saying an atomic clock is made for us to see the time like a wristwatch, duh, but the real purpose is extremely high timing accuracy.
Edited by xnor - 12/22/13 at 9:28am