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Hey all,

Last week I managed to do a 32kHz cap via S/PDIF using our PowerMac G5 almost without issue - hurray! Thanks to everyone who chimed in, esp re the clarifications about what '12-bit' meant in the context of DAT LP recording, and to John Gledhill, who graciously called me and discussed SPDIF capture issues at length and provided a test signal. Two small notes - on older versions of OS X (10.3), apparently the optical input had to be set to use the external SPDIF clock, using the Audio MIDI Setup application. On 10.4 Tiger on these machines, this option is greyed out, and the external clock is used by default. Also, if you are trying to capture a mixed frequency DAT, Audacity will crash on the freq changeover. Upon recovering Audacity though, it should have your entire cap before the changeover (it did for me). Still, if you'd like to avoid this, don't leave your cap unattended (which I should not have done; moment of weakness). 

Separately, we ended up getting one of the CM6206-based USB sound cards I mentioned in my initial posting (quoted below), which reputedly had the ability to capture 32kHz input via its SPDIF in, in the hopes that we could use our other, less-obsolete computers to do caps. Sadly, a) even without any input at all, all that's coming out of its S/PDIF input is a wall of loud noise and b) in OS X Audio MIDI Setup, it does not offer the option of recording at 32kHz at all, only at 44.1kHz or 48kHz. This happens on both the G5 and on our other Macs, so my guess is that the card is shoddy (surprise!) and the 32kHz functionality is disabled on the card or in the driver, if it's there at all. (According to the datasheets, even for the newer version of this chipset, it should, but how knows). Even if it's just disabled in the driver, it is probably not worth trying to edit the kext to get it to work. So, this route appears to be out, on the off-chance anybody was considering it. A real shame. 

However, I'm realizing now that our other office workstations (if you could call them that), late-2009 model Mac Minis (aka MacMini 3,1) have mini-TOSLINK/3.5mm TRS jacks for both input and out. I had previously missed this because the Sound preference pane made no mention of a Digital Input, and have comparatively little experience with actual Macs. I stumbled across this by opening up System Information. My guess is, plugging in a mini-TOSLINK cable to the line-in port will 'activate' the input in OS X (I've observed similar behavior when plugging in and disconnecting headphones). Can anybody confirm this? Does anybody here have experience using this input?
Aside from that - from what I can tell, unfortunately, this Mac probably - no datasheet to this effect, just some Googling and guessing - uses a Realtek ALC88x chipset (which is listed in system information as 'Intel High Definition Audio' - this is a standard akin to AC97, not an Intel chipset per se), and of these, only the highest-end ALC889 supports 32kHz input. I will be testing to confirm my suspicions as soon as I can but am not too hopeful.

Again, all ears. If this doesn't work out, we can use the PowerMac G5 for these caps, but that is not ideal for the long-term - obviously the computer is obsolete, somewhat slow, and something of a power-hog, and if it breaks, repairing it is probably a dubious proposition. So - if anybody knows of any SPDIF capture card or box that can do 32kHz caps and doesn't cost too much - say, $50 maximum - please chime in. Otherwise, probably the most economical solution (as well as the least, er, technically janky) to capturing 32kHz or mixed freq DATs, without an analogue intermediary, for those who have not already invested in SPDIF capture equipment and otherwise have no use for such, is using a SCSI DDS drive. But I was hoping to discover a cheaper, reliable alternative that still worked, and would still love to find it.

Thanks everyone for your time!
Eli

May 2 2017 1:56 PM, "Eli Bildirici"  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