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. -- Matthew Skala [EMAIL PROTECTED] Embrace and defend. http://ansuz.sooke.bc.ca/ _______________________________________________ Cinelerra mailing list Cinelerra@skolelinux.no https://init.linpro.no/mailman/skolelinux.no/listinfo/cinelerra
