On Sat, 9 Jun 2001 andy at theasis.com wrote: > > Nope. Can refer to whatever you want. Power is the most common use, > > however. > > I still think such usage is a distortion; still meaningful, maybe, but > really ouside of the scope of the formal definition. In other words, by > definition, the number of bels is defined as the common logarithm of the > ratio of two powers. Since you have references, see if the definition > specifies powers. Yes, that is the formal definition, no question. The original paper was Martin, W. H., "Decibel: The Name for the Transmission Unit", Bell System Technical Journal, 1929. From a textbook definition, you are strictly correct. However, as you pointed out, power is proportional to voltage, so it is valid and common practice -- probably _more_ common these days, when we have active output stages driving voltage mode input amplifiers -- to pull the exponents out and talk about dB w.r.t. voltage as 20log(v_1/v_r). The main point is you have to nail down v_r, and dB has turned into just a log scale. > I think that's all the more reason that the definition relies on power. If > you're talking about the metric of change to be voltage, you need to say > so, otherwise it's not clear whether you double the stuff with 3 or with 6 > dB. So what's the right relationship to use for your salary example? If I say dBFS, I have said. I didn't originally, hence this awful little thread. ;) I'd use 6dB for the salary example, because it's potential and voltage is potential. If you were talking about money being spent, that'd probably be 10log, because it's purchasing power. But you're right -- we're getting pretty far removed from the point. > Well, any person will likely be versed with a subset of the idioms. I > *should* have been able to think in terms of bits for the digital sampling > environment for .wav files, but you had to remind me. Nah, I didn't _have_ to. That's just the kind of guy I am. :) > As mentioned, it's not obvious what to do with dB$. Or I'm still > missing something (Highly likely). No, you're just keeping me honest, after years of throwing dB around without regard for people's feelings. > > Correctly! I'll bring a book the next time we get together. It's a > > little bit confusing until you sort out all the different dB scales. > > They're gonna send us to a different table. Or a different bar. If only the library had a liquor license. -- "To misattribute a quote is unforgivable." --Anonymous