 |
 |
Fascinating. Thanks for explaining this. I wasn't 100% sure what non-linear meant in this context and didn't want to derail, but hey, might as well. So the output after having been remapped using decode_lp_sample or similar is 16-bit. How did e.g. Mr Taylor in that function arrive at those values for this look-up table though? May 2 2017 3:54 PM, "Dave Rice" <[log in to unmask]> wrote: > Hi Eli, > As noted, the use of 12 bits is not linear but it's a selection of some of the values of the 16 bit > range that are mapped to 12. AFAIK all of the DAT rippers that support 12 bit do so with a lookup > table in order to map the 12 bit value to the corresponding 16 bit value. For instance see the > decode_lp_sample function, https://github.com/andrew-taylor/read_dat/blob/master/read_dat.c#L1067, > which is used in both DatXtract and read_dat. > Dave Rice > >> On May 2, 2017, at 3:15 PM, Eli Bildirici <[log in to unmask]> wrote: >> >> Hey Lou and Ted, >> Appreciate it but I'm trying to avoid the quality loss, however minor, of a D-A-D conversion. Once >> the 12-bit files are created, resampling to a more standard format e.g. Redbook should be trivial >> by using a good resampler like SoX (or Izotope if you could afford it) right? In any case there is >> also Redbook and possibly 48kHz content on these tapes and it just seems silly to do D-A-D on >> those, lacking even the motive of moving to a more standardized format. I'm only even asking for >> this because I figured it would be beneficial to know an alternative to the preferred way of making >> these copies (DSS drives and ReadDAT or DATXtract). Of course if neither of these ways work out, >> doing a D-A-D conversion will have to do, and probably won't make much of a difference given that >> there is very little content here that isn't straight-up voice (we're a radio show after all). But >> it's still not ideal :/ In any case, thanks for chiming in. >> Regards, >> Eli > > May 2 2017 2:48 PM, "Ted Kendall" <[log in to unmask]> wrote: > If memory serves, the 12-bit convertors were non-linear anyway. Best to > convert to something civilised via analogue. > > May 2 2017 2:24 PM, "Lou Judson" <[log in to unmask]> wrote: > Sigh, nonstandard formats are a problem! > > But as a small time archivst myself, I would take the analog outut of the deck and re-encode it at > 16 bit for archiving purposes. There is no way you waould actually want “bit-perfect” 12 bit files, > as that would just pass the problem down to your successors. > > Play the DATs, record the output in a normal format, and it will be far better than any kluge you > can do with 12 bit digital. > > I used Sony 12 bit 32kHz for some extended recordings back in the day, and this was the best way I > found for the transfer. > > I’ll be interested to see if anyone has a better suggestion! > > <L> > Lou Judson > Intuitive Audio > 415-883-2689 > > On May 2, 2017, at 10:56 AM, Eli Bildirici <[log in to unmask]> wrote: >> Hey ARSClisters, >> >> I'm an intern in the archives department at Democracy Now! and have come across a couple hundred >> mixed-frequency DAT tapes, many of which have 12-bit/32kHz content on them. (And yes, this is the >> same issue an archivist from DN! posted about nearly ten years ago, here >> (http://www.cool.conservation-us.org/byform/mailing-lists/arsclist/2007/07/msg00380.html).) We'd >> like to make bit-perfect digital copies, but don't have a SCSI DDS drive at the moment, and in any >> case would like to know if there's a reliable alternative path to digitally copying DATs, >> especially those recorded at a bit-depth of 12, via S/PDIF and capture cards. I attempted to copy a >> portion of a tape recorded at Redbook rates using our main deck - a Sony PCM-R500 - with an M-Audio >> FireWire Solo and Audacity to record, but this was full of pops and clicks that, I assume, are the >> result of the M-Audio failing to lock onto the tape deck's clock. (The pops and clicks only show up >> during recording and are not on the tape itself. Actually, I suspect Audacity may in part be to >> blame, since the pops and clicks are absent when monitoring via the M-Audio control panel app on OS >> X...but I digress.) I've also found that external sound cards based on the C-Media CM6206 chipset - >> cheap and plentiful on eBay - reportedly support 16-bit/32kHz input, as does the S/PDIF input of >> our aging PowerMac G5. But that doesn't help us with 12-bit content, and nor do we know whether >> clock syncing will pose an issue and how to deal with it if it does. My suspicion is that, while >> there might be an economical and reliable solution to recording DAT tapes with 16-bit content (at >> least at 44.1 or 48 kHz sample rates) without a DDS drive, that we're out of luck for 12-bit >> content - but, any advice/confirmation/refutation would be most welcome. >> >> Thanks, >> Eli >> >> Eli Bildirici >> (347) 837-8337 >> >> Eli Bildirici >> (347) 837-8337 Eli Bildirici (347) 837-8337