Understood Michael. The underlying mathematical principles of digital manipulation are the same for all data stored as 1s and 0s, but I'm guessing that the same processing techniques are used with slightly different objectives in mind depending on the application. For instance, in digital audio, noise shaping is used to apply dither in such away that the random noise is applied less in the most sensitive frequencies of human hearing and more in the very low and the high frequencies where sounds need to be louder to be audible.
Also, I think that digital audio is a lot more sensitive to minor errors and that you can't get away with the same approximations that you can in the video/imaging world. In other words, it is possible to *hear* non-linearities and correlated noise which you wouldn't be able to *see* in an image (or which wouldn't be so objectionable). I got a little confused earlier, but I'm coming round to the fact that stepping up in word size from (say) 16 to 24 bits is a trivial operation if you just insert zeroes. On the other hand, resolution enhancement, as performed by the Meridian 518 and lots of other high-end audio devices, is something "extra". As I posted earlier, 'this white paper from Wadia' (http://www.wadia.com/technology/technicalpapers/Resolution_Enhancement.pdf) gives a very good description of resolution enhancement and shows why one might want to step up from 16 to 24 bits -with the addition of dither-. As far as up- or re-sampling is concerned, the samples *are* modified in a non-trivial way and I am certain that applying dither is a *mandatory* part of the process. I urge you to read read pages 37-40 of the 'Meridian 518 handbook' (http://www.meridian-audio.com/download/Handbooks/500_Series/518user.pdf) (if not the whole thing). It's not an easy read, but there is so much information in there about digital audio processing from one of the true pioneers and experts in the industry. BTW, I will be experimenting with the following sox command line later today. Because ringing is a product of steep filters, I've decided to try a more relaxed filter with a bandwidth of 90.7% (which corresponds to an (IMO) acceptable upper filter frequency of 20kHz). I'm also, for the time being going to allow aliasing beyond the upper cut-off, but I may turn off that option if the bandwidth relaxation reduces ringing significantly. I'm also using the sox equivalent of Meridian's "high pass" TPDF dither. I'm not using any volume modification at present, and I'm reluctant to do so unless I find that it is absolutely necessary. Code: -------------------- flc flc squeezebox 00:04:20:10:14:eb # FT:{START=--skip=%t}U:{END=--until=%v} [flac] -dc --totally-silent $START$ $END$ -- $FILE$ | [sox] -q -t wav - -t flac -C0 -b24 - rate -v -M -a -b 90.7 88200 dither -S -------------------- -- VirusKiller ------------------------------------------------------------------------ VirusKiller's Profile: http://forums.slimdevices.com/member.php?userid=19799 View this thread: http://forums.slimdevices.com/showthread.php?t=69454 _______________________________________________ ripping mailing list [email protected] http://lists.slimdevices.com/mailman/listinfo/ripping
