Thanks Matthew. Very clear. It's the base for my understanding. Ciao Raffaella
On Sat, 2006-09-30 at 11:07 -0400, [EMAIL PROTECTED] wrote: > On Sat, 30 Sep 2006, Raffaella Traniello wrote: > > On Internet I learned that we can hear from silence (0 Db) up to over > > 140 Db (a bomb). > > So why to set the automation range from -80 to 6? Are these number > > referred to Db? > > The dB scale actually measures *ratios*, or differences in loudness, not > absolute levels. So it's not really meaningful to say "The level of this > signal is 10dB"; all you can say is that "This signal is 10dB above that > one." > > Nonetheless, people do use it to measure absolute levels, and they do that > by choosing a specific reference to be 0dB and then describing where > everything else is in relation to that reference. > > For actual sounds in the physical world, the usual zero point is chosen as > the softest sound a typical human can hear. That's 0dB (more correctly > 0dBA - the "A" indicates that we're using this scale). Louder sounds are > like 20dBA for whispering, 60dBA for typical spoken conversation, or your > example of 140dBA for a bomb going off. Note that 0dBA is *not* truly > "silence"; it's just the softest sound audible to human hearing. > > But electrical signals are usually measured on a scale where 0dB is taken > to be the loudest sound the system can reproduce accurately. In normal > use, typical signal levels will be slightly below that, with peaks going > slightly above. You will get distortion as you go above 0dB signal > levels. On level meters there's a red zone on the scale to warn you about > that. Depending on the user's volume setting, 0dB on the electrical level > meter might be 60dBA or 80dBA or 20dBA or whatever. > > One issue with digital is that in most cases the top of the power scale is > a hard limit - once your signal's 16-bit sample values get to +32768 you > simply *cannot* go to +32769. As a result, the "clipping" distortion you > get when you drive a digital system past its maximum tends to sound > especially annoying, and you have to be really careful not to do that too > often. Analog systems tend to degrade more gracefully, so that you can > push them above 0dB on the level meter with audible, but not annoying, > distortion. A similar effect is part of why some people fetishize > vacuum-tube analog amplifiers: the way they distort at excessive signal > levels is claimed to be better-sounding than the way transistor-based > amplifiers do. > > Electrical equipment displays a phenomenon called the "noise floor", which > means that there is *always* some amount of noise measurable even when > there is no signal. You can never have true silence. The noise floor > might be 80 or 100dB below the 0dB mark on your level meter; it depends > very much on the quality of the equipment, with better equipment having a > lower noise floor. With 16-bit linear digital samples, there are > theoretical reasons that the noise floor can't be any lower than about > -98dB. So it makes no sense to have volumes adjustable below that. In > Cinelerra, there is a configuration setting for how low you want the level > meters to go. > > > What numbers have I to write if I want silence when the white fade line > > is at the bottom margin of the track and a slightly too loud sound when > > the line is at the top margin? > > The defaults should be like that already. _______________________________________________ Cinelerra mailing list [email protected] https://init.linpro.no/mailman/skolelinux.no/listinfo/cinelerra
