> Now decibels are not anything as far as Psychophysics -- whatever that is! OK, what I was referring to is a (possibly manufactured) recollection of a correspondence between 1 dB and the minimum difference detectible by human audio perceptual apparatus. Psychophysics is concerned with the translation of perceived differences into "actual" differences. I.e., how much more amplification (power) do you have to apply to make something seem twice as loud, or twice as bright. How much more weight to seem twice as heavy. Note I'm putting things in terms of ratios. > ;) -- decibels are simply one tenth of a bel, which is a unit of relative > change. They are very handy for electrical, acoustical, and a couple of > other log scale measurements, Keep in mind that there is in fact always a reference against which to compare any sound that hits an eardrum or a microphone membrane: the sound pressure level caused by air molecules bouncing around on the membrane. This baseline becomes, in effect, the tared 0 point, because both inner ear pressures are equalized in terms of that. (Aside: I've not yet successfully thought through how this translates to pressure on either side of a microphone membrane.) If you've ever stepped into an anechoic chamber you know what I'm getting at. Anyway, the above correspondence I mentioned does exist, but it may be true that it just happened to work out that 1dB over background is pretty close to the minimum detectible change in sound pressure level. OTOH, I'm probably just wrong. I'll have to go check on that one. > but you could just as easily say that Joe who > makes $20k/year earns 6dB$ less than Sue who makes $40k/year. I think I disagree. First, I think it has to refer to power. I guess you can make a case to call $ power, but that's rather a departure from what the Bell Labs folk were addressing. Really, though, as soon as you get outside of power (into Voltage or Sound Pressure), you're dealing with additional translations. Also I think you want to say s/6/3/ dB, since log10(2) = .301, meaning a doubling of _power_ (or $) is 3.01 ~ 3 dB. Um... Remember that power is proportional to (voltage)^2, so using 6dB would be appropriate if you were talking about voltage instead of power -- a doubling of voltage is a 6dB increase or a power ratio of 4. > You have to specify the units, which in this case are understood to be > dBFS (decibels w.r.t. Full Scale -- whatever $MAXVALUE is for your > wordlength.) Ahh, ok. Except the part of being understood. As mentioned above, my inclination is not to reference Full Scale by default. > Does that make it make more sense? That last part does clarify it quite a bit. Also you did force me to think hard enough to organize the ratio thing a bit more. But the power vs. voltage thing still leaves me wondering how this software is operating on the sampled signal in the .wav. Andy > Phil