On Tue, 2012-12-11 at 15:31 +0100, Alessio Elmi wrote: > but don't you think you loose a lot of > information by doing this normalization?
Alessio, setting up the programme chain in a radio or tv or anything else is a constant trade off between the highest electrical level the sound will produce, and the ability of the system to reproduce this faithfully. Cowboy is right. In the Analogue days A amps and B Amps were set up to handle at least 20db of overload before distorting. We monitored using 'VU Meters' which by their very design showed an average of the signal, and definitely did not show peak audio levels. There were 'peak programme meters' which were faster, harder to follow, and they too did not show all the peaks. The only really good meters we had were oscilloscopes which could show voltage peaks and I can confirm that '0 on the meter' included a whole lot of data that went well beyond that. All the amplifiers in the system were designed to have as much headroom as possible and even when you did overload them the onset of distortion was gentle, so those peaks were not so noticeable if they did distort. The combination of vacuum tubes and the circuitry surrounding them that allowed for variations in performance as the tube aged meant the distortion crept in as you reached overload. That is not so in the 'digital' era where there is *NO* margin above whatever headroom you have. Trading 13 db of signal to noise to avoid distortion is not a bad trade off because audio peaking too high goes from no distortion to pretty much 100% distortion instantly. at the noise end of the dynamic range 13db is not a big deal because most of what we get from CD is well within 60db range and the CD standard has a noise floor below 73db so we're still 'in with a grin' by about 20db The dynamic range of 16 bit 44100 audio is far greater then the dynamic range of anything in the transmission path, so there will be some gain manipulation in the path. By setting -13 we have a system which gives a reasonable margin before distortion. OK in a controlled studio situation. Recording live with digital gear I tend to run closer to -20 to allow for the unexpected peaks that just come along. In a perfect world you could run all your audio at 0, but having looked at a few spectral analysis read outs I can tell you those pesky peaks just happen along and ruin your day. Once you have distortion you can't get rid of it. I think you are confusing 'normalisation' with what is called 'compression' [mp3 etc] but is in fact "selecting just enough to retain a semblance of the original but in a smaller file" which in my view is an electronic sham. There are places where 'compressed' audio is fine. We use mp3 for news tracks. Reducing file size for distribution make sense. In the compromise that all audio broadcasting involves, setting the normalisation level at -13 is not a bad decision. The sound card will turn this into anything from -20dBm to +4dBm which then goes to the desk, if you run that way, or may be routed as digital to a digital mixer. Yes the output will be 13 db below the maximum the sound card can deliver, but it won't be distorted. regards Robert Jeffares Big Valley Radio Thames _______________________________________________ Rivendell-dev mailing list [email protected] http://lists.rivendellaudio.org/mailman/listinfo/rivendell-dev
