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Digital transfer of DAT tapes to computer

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Re: Digital transfer of DAT tapes to computer

Postby Hugh Robjohns » Thu Apr 26, 2012 10:22 am

shams wrote:I have the optical cable now to connect the DAT player to the MacBook, but I can't get a signal. Same problem when I hook it up to the line in on my Sony PCM-D50 recorder, which also has optical in. After reading around, I'm starting to think the problem is that the tapes were recorded on long play and thus at a lower rate that's not supported by the MacBook or the recorder (both of which have floors of 44.1 kHz).


The long-play mode on DAT machines uses a 32kHz sample rate with 12-bit non-linear encoding and a frequency response that extended to about 14.5kHz.

The issue may well be to do with the 32kHz sample rate being incompatible with your Mac, but I wonder also if the machine can output S/PDIF in this format at all because of the need to transcode between 12-bit non-linear and the 16 bit linear format required by everything else.

Edited to add: The other possibility is that the recording has been flagged as copyrighted and the SCMS system is preventing anything else from recording the data digitally.

Given the inherently limited quality of the source recordings in long-play mode, I would suggest that taking the analogue outputs (most DAT machines can replay long-play DATs even if they can't record them) and re-recording through a normal computer interface via the analogue domain might be the most pragmatic way forward.

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Re: Digital transfer of DAT tapes to computer

Postby ef37a » Thu Apr 26, 2012 10:46 am

Again. I am DAT stupid but both the aforementioned Sony MD and Philips DAC used "mucked about" coding systems and yet both output a normal digital signal (one is co-ax and one optical but a five quid converter works fine)

The mindisc machine even has a mono, lp mode and although I have not tried it I can see no reson why that should not feed standard S/PDIF out? It is after all a SONY/PHILPS connection protocol!

But I agree Hugh. Little or nothing should be lost going from the analogue line outs. In anycase, for all we know they might just take the line out and S/PDIF it!

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Re: Digital transfer of DAT tapes to computer

Postby Hugh Robjohns » Thu Apr 26, 2012 11:16 am

ef37a wrote:...Sony MD and Philips DAC used "mucked about" coding systems and yet both output a normal digital signal ...

I think you mean Philips DCC, but yes, quote so. It is obviously possible to transcode between a non-linearly quantised or a data-reduced format to a linear one, and in the case of MD and DCC it was a pre-requisite of the system.

The long-play mode in the DAT format was an option (mode III) that not all machines supported, and some only supported replay but not record. To be honest, it's not a mode I ever used and so I have no first hand experience of whether typical machines would or could output S/PDIF for long-play tapes or not. I was just raising it as a possible issue that might warrant further investigation.

S/PDIF can certainly handle the 32kHz sample rate.

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Re: Digital transfer of DAT tapes to computer

Postby chris... » Thu Apr 26, 2012 11:40 am

Hugh Robjohns wrote: I wonder also if the machine can output S/PDIF in this format at all because of the need to transcode between 12-bit non-linear and the 16 bit linear format required by everything else.

Transferring a load of long-play DATs awaits me...

Assuming my computer interface and software can handle 32kHz sample rate, then *if* the DAT machine outputs anything at all on the S/PDIF port, *then* it should be 16 bit linear format, right ?

ie. so I hopefully won't have to worry about somehow converting from the 12-bit non-linear format myself, in the computer ?

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Re: Digital transfer of DAT tapes to computer

Postby Hugh Robjohns » Thu Apr 26, 2012 12:03 pm

Yes, if it sends data down the S/PDIF pipe, it will be formated as linearly quantised audio.

I've had a rummage around a few Sony DAT manuals and can't find anything to suggest that long play tapes won't output valid S/PDIF, so I presume it works as you would expect, with a 32kHz sample rate.

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Re: Digital transfer of DAT tapes to computer

Postby Tomás Mulcahy » Thu Apr 26, 2012 12:06 pm

The last time I had to do this (about 1998?) it was a Tascam DA20 mark 2 feeding S/Pdif to a Korg 1212 PCI card. The card locked to the 32kHz rate and I recorded as 16 bit in Cubase VST, sounded fine considering the limitations of DAT LP mode.

So I think the earlier problem was because the Mac does not support 32kHz. Most audio interfaces do though.
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Re: Digital transfer of DAT tapes to computer

Postby Hugh Robjohns » Thu Apr 26, 2012 12:12 pm

Thanks Tomas -- that's reassuring to know.

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Re: Digital transfer of DAT tapes to computer

Postby chris... » Thu Apr 26, 2012 12:48 pm

Hugh Robjohns wrote:Yes, if it sends data down the S/PDIF pipe, it will be formated as linearly quantised audio.

Thanks chaps - will give it a whirl and report back. I too have a Tascam DA-20mk2.

The real fun may be DAT tapes that are partly long-play, and partly standard-play. Have a feeling analog may be the way to go for those...
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Re: Digital transfer of DAT tapes to computer

Postby ken long » Thu Apr 26, 2012 12:54 pm

chris... wrote:

The real fun may be DAT tapes that are partly long-play, and partly standard-play. Have a feeling analog may be the way to go for those...

multiple config DATs with different SRs shouldn't be a problem via S/PDIF. Obviously, you will need to record however many passes you need. Analogue out won't be a big loss but if yyou can do it right, why not? :)
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Re: Digital transfer of DAT tapes to computer

Postby chris... » Thu Apr 26, 2012 1:03 pm

ken long wrote:multiple config DATs with different SRs shouldn't be a problem via S/PDIF.

I guess I'd need to (Plan A) set the computer for 32kHz, and transfer that part of the tape. Then stop, set the computer for 44.1kHz, and then transfer the next part of the tape etc.

I'm thinking I'll find it easier to let the DAT run from start to end, and then do all the editing on the computer afterwards.

Are you suggesting I (Plan B) transfer the whole tape at 32k, and on the computer, locate and cut out the bits that are really 32k. Then transfer the whole tape again at 44k and on the computer [...]. I guess that might just work, if use a lot of DAT-head hours.
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Re: Digital transfer of DAT tapes to computer

Postby Hugh Robjohns » Thu Apr 26, 2012 1:18 pm

That won't work, the sample rate via the S/PDIF will keep changing nad the computer will either keep stopping or flag files with the wrong sample rate.

If the tapes really are of mixed format, then going analogue is the sensible approach -- the universal sample rate converter -- as everything will end up with the same sample rate in the one project. Much easier to deal with, and the quality loss will be negligible via any decent modern A-D converter which will be an order of magnitude better than those of the original DAT, or the DAT's D-A.

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Re: Digital transfer of DAT tapes to computer

Postby chris... » Thu Apr 26, 2012 1:49 pm

Hugh Robjohns wrote:That won't work, the sample rate via the S/PDIF will keep changing nad the computer will either keep stopping or flag files with the wrong sample rate.

Right. Makes sense.

I guess I'm keen on digital transfer to avoid the hassle of setting analog input levels. Could record at 24bit, but that seems wasteful of space, given the task in hand. So more likely I'll record at 16bit, and set the level carefully. (Tho' I guess I could record at 24bit, normalise, then dither down to 16bit, without noticeably affecting things).

Try to not laugh much, but the only A/D converter I currently have to hand is Yamaha 01V mixer from 1998 (going ADAT to computer). Not the latest+greatest converters, but will probably do.

Edit - also have a little Sony PCM-M10 flash recorder with line-in, which is 10 years newer than the DAT, so might just have better converters.
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Re: Digital transfer of DAT tapes to computer

Postby ef37a » Thu Apr 26, 2012 2:45 pm

Surely this is no different from importing a mixture of 44.1kH and 48kHz files?

I am fairly sure I could do this in Samplitude then SAVE everything at 44.1kHz.

My son regulary records things from BBC R3 on the web in realtime and saves it as a 44.1kHz 16bit.wav which it assuredly is not originally! Same goes for Youtube sound.

But then I have probably got it all wrong!

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Re: Digital transfer of DAT tapes to computer

Postby Hugh Robjohns » Thu Apr 26, 2012 2:53 pm

chris... wrote:I guess I'm keen on digital transfer to avoid the hassle of setting analog input levels.

But it couldn't be easier! The absolute peak level is a known quantity, and any modern A-D will have more headroom capability than you could ever want while still having a lower noise floor than the DAT machine's D-A. So all you have to do is find the loudest bit on tape, set the record level of your interface to make that peak to a comfortable level -- say peaks to -4dBFS or so, and let it get on with it!

Could record at 24bit, but that seems wasteful of space

Totally trivial and irrelevant concern with typical hdd sizes today. I'd record 24 bit with headroom. Tweak the material as you want, and then bounce to 16 bit if you feel the need, having removed the surplus headroom.

Edit - also have a little Sony PCM-M10 flash recorder with line-in, which is 10 years newer than the DAT, so might just have better converters.

Probably so, yes. The O1V's converters weren't its greatest strength.... but even so, I reckon you'd be hard pressed to hear any significant deficiencies compared to the 12-bit non-linear long play DAT mode.

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Re: Digital transfer of DAT tapes to computer

Postby ken long » Thu Apr 26, 2012 2:54 pm

Not when the DAT device is acting as the master clock, Dave - which is the only way to digitally migrate the data.
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