litepipe wrote: > This may sound stupid, Not at all, actually! > but I'm wondering why do we even use VU Meters? > I understand that it shows us more of the "comon" level but shouldn't we > really be watching the peaks to see where the level is too hot? What do > we get from VU that we don't get from PPG? I'm just a little confued as > to their uses. I understand what they do now, using them is the > problem:-P Thanks!! It's also partly a 'Europe versus USA' thing! The VU 'standard' was cobbled together by Bell Labs, CBS and NBC back in the late 30's or early 40's. They optimized it for radio broadcasting primarily, but for all sound recording in general. There's an ANSI specification for it but I'm afraid I don't know it off by heart. In order to determine 0 VU in the ANSI spec, a sine wave of +4 dBu is used. As I said earlier, it's deliberately concocted to have a slow response: it's intended for it to take 300 ms to reach 99% of its full deflection under any given aural input. Its overshooting or clipping must also lie within the range of 1-1.5% and not more. Useless for peaks. The PPM system is European. To be honest, it's the more valuable one for digital recordings simply because it's far better for preventing clippings and overs. Unfortunately, there are several different PPM specs doing the rounds in Europe even now! Technically speaking, peak programme meters do not respond "instantaneously". Instantaneous must be defined because it's basically impossible to realize an electrical signal in which one has integrated over an infinite span. PPM's simply must have a finite integration time so that peaks wide enough to be audible are displayed. The DIN specification is probably the most commonly used although the BBC one is quite common too. I looked them up the other day out of interest but I'm afraid I can no longer remember them. It's to do, though, with a difference in attack times for any transient, and the degree of response to those attacks. Those don't really answer your question, although I think they establish the necessary background. Suppose you've been asked to record (a) a funeral conducted by a group of ants who happen to live right by the take-off runway at an airport ... and (b) you've been asked to provide some background noise from a cocktail party for use in say a theatre production. In the former case, if you worked only from the peaks (using PPM) then there'd be complete silence on your recordings excepting only the occasional loud aircraft. Of course, you could also try "riding the meters" by watching out for them airplanes and turning your meters down whenever they came by, and then returning your focus to the ants at the point in between. Which is really rather the point here ... your focus is on the occasional airplane that comes by and not upon the ants which you are trying to record. On the VU system you would just set your level for the ants and pretty much have done with it because the occasional airplane wouldn't really trouble you except that you might the first time have to nudge your recording level down a notch to make sure that ... in general ... you recordings as a whole weren't clipping. As for the second scenario of the cocktail party, since you're definitely not interested in any peaks but rather than in the average overall level, the VU method is definitely superior. You don't have to worry about the occasional clink of glass or any such because you're don't want anything to stand out and you don't need anything to stand out. Then ... the standard broadcasting (and also partly mixing) problem is ... how do you get the volume levels of many many different sources to blend together into one acceptable continuum (think, adverts in the breaks between different radio or TV programmes). The answer is you use VU meters to keep the overall general level within certain aesthetically acceptable limits. Thus you could have a documentary on the ecological behaviour of ants who live near an airport followed immediately by a programme on the evolutionary behaviour of human beings who attend cocktail parties, with as many advertising breaks as you like between them, and everything would match in audio levels without consumers having to keep jumping up and turning their volume controls up and down in spite of the widely differing acoustic environments. Peaks and VU's are both useful which is why they are both there, although with digital recordings peaks have really become pretty close to essential in a way that they weren't before. Hope that makes sense. Kool Musick Keep Musick Kool > --Roger > > > > > >Yahoo! Groups Sponsor >ADVERTISEMENT ><http://rd.yahoo.com/M!5002.1818248.3328688.1261774/D=egroupweb/S050 07334:HM/A„7665/R=0/*http://ads.x10.com/?bHlhaG9vbW9uc3RlcjcuZGF016718564%3 eM!5002.1818248.3328688.1261774/D=egroupweb/S05007334:HM/A„7665/R=1>2f42 eb.jpg >2f4363.jpg > >Your use of Yahoo! Groups is subject to the ><http://docs.yahoo.com/info/terms/>Yahoo! Terms of Service.