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Author Topic: Portable DAT modded to 24-bit?  (Read 1411 times)

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Offline jefflester

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Portable DAT modded to 24-bit?
« on: June 05, 2020, 12:19:32 PM »
There's a taper "BobS" sharing some of his DAT masters from the 2000s on Dime and he was calling them 24-bit so I pointed out that the "M1" was 16-bit DAT recorder not 24 and he says it was modded. I could maybe see possibly a home deck (playback is on a Sony 7040) getting modded to 24-bit playback but have a hard time believing such a mod could be done on a small deck like an M1. Anyone ever hear of such a thing or how it could have been done?

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#8400232 by bobs23 at 2020-06-05 14:43:13 GMT
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In comment #8399978 tdcrjeff wrote something like this:

"Recording gear: DSM6-EL>M1 DAT with Sonic Studios pre amp mod at 48/24
Transfer deck: Sony PCM-7040 out 48/24 "

There were never any 24-bit DAT portable recorders, and certainly not the "M1", which presumably means Sony PCM-M1. AFAIK, the only DAT machine that ever did 24-bit was the $2000 Tascam DA-45R 3U deck circa 1999 , which ran double-speed for the increased word depth - only 1 hour recording on a 2 hour tape.



Having worked in the entertainment industry in LA for a very long time, I have some very smart friends that have the ability to not only fix gear, but to modify it as well. The A/D's and associated circuitry were moded to make this happen. Take it or leave it.

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Offline Craig T

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Re: Portable DAT modded to 24-bit?
« Reply #1 on: June 05, 2020, 12:55:54 PM »
The stock PCM-M1 used the AK4520A a/d chip, which was 20bit.  My guess is that the modification was to replace the AK4520A with a 24bit a/d chip.  I'm sure the modified M1 was still recording at 16bit.
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Offline jerryfreak

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Re: Portable DAT modded to 24-bit?
« Reply #2 on: June 06, 2020, 12:32:28 AM »
id call BS on that

as you mentioned, you'd literally have to mod both the ADC circuit writing to the DAT, and either insert some novel compression algorithm between the ADC and the tape, or as you mentioned, physically speed the tape up, to fit the data on it. Thats a ton of changes in a deck of that size (remember how small the M1 was relative to the D8?)

reading the tape back would require a custom DAC to decode this mysterious, non-standard 24 bit data

more than likely this guy dumped his entirely 16-bit signal path into a 24-bit soundcard with 8 empty bits (or worse, into a non-bit accurate soundcard that filled up 8 bits with noise). The fact that the guy doesnt even understand how critical the soundcard is, and doesnt list it in his lineage, is also a red flag

none of it makes any sense. doing any mod like that would be prohibitively expensive and money thrown at better mics or a real preamp would return far greater results. And its not like there werent real 24bit recorders in 2006
« Last Edit: June 06, 2020, 12:49:21 AM by jerryfreak »
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Offline jerryfreak

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Re: Portable DAT modded to 24-bit?
« Reply #3 on: June 06, 2020, 12:37:05 AM »
also i vaguely remember some 20 bit or 24bit mods to equipment of that era.... sbm maybe. but i think it was just to use better chips, not necessarily all the bit depth

my $50 sony voice recorder uses a SoC capable of 32bit/192K, but only utilizes 16/44
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Offline Scooter123

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Re: Portable DAT modded to 24-bit?
« Reply #4 on: June 06, 2020, 02:37:51 AM »
Nah

The SBM dithered and truncated down the signal to 16bits.  I've used it extensively when I transcribed somewhere in the neighborhood of 1,000 DATs a couple years ago.  However, there is a HOSA equivalent which does the same thing but outputs to SPDIF, a preferred cable, rather than the Sony 7 Pin. 
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Offline jerryfreak

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Re: Portable DAT modded to 24-bit?
« Reply #5 on: June 06, 2020, 02:53:33 AM »
lifting the veil for tech talk in interest of clarity.

Nah

The SBM dithered and truncated down the signal to 16bits.

SBM did utilize dither on the LSB (which is different from truncation), however dithering was not its purpose. The 'noise shaping' employed by Sony's SBM technology is rather novel and is a good technical read, of how they were able to shove 20 bits of audibly-weighted data into a 16-bit bag. It was so counterintuitive to me that i had to read the details on it to understand it fully

I've used it extensively when I transcribed somewhere in the neighborhood of 1,000 DATs a couple years ago.  However, there is a HOSA equivalent which does the same thing but outputs to SPDIF, a preferred cable, rather than the Sony 7 Pin.

im not sure there is another common device that did what the SBM did, fundamentally. Sony had their noise-shaping technology well patent-protected

Regardless, SBM would be useless in a DAT-transfer scenario, as it is an ADC codec, which isnt employed in (proper) digital transfers

as for S/PDIF, it is the format used on both coax and the proprietary sony connectors (as well as toslink). Yes coaxial cables are more universally useful, but its the same S/PDIF format in all cases. There are numerous 'converters' made by Hosa, M-audio, etc that adapt one to another but its S/PDIF in all cases (some use I2S but as I understand, that is not necessarily ideal unless you are intent on reclocking)

the '24bit SBM' or whatever it was (i cant remember).. was an oddball mod scenario i read about here, again, where the full advantages of the bitdepth was not realized due to technical limitations of the surrounding hardware
« Last Edit: June 06, 2020, 03:18:21 AM by jerryfreak »
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Offline Brad Manning

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Re: Portable DAT modded to 24-bit?
« Reply #6 on: June 06, 2020, 01:30:24 PM »
The dude on DIME is either full of sh*t, or deeply ignorant, plain and simple.

There has never been a portable Sony DAT recorder with the ability to record anything other than a 16 bit PCM signal or DSD, even with an outboard A/D that captured in 20 or 24 bit like Apogee units could do.

The word length on a DAT tape is 16 bit, but you can import in Wavelab or Audacity using 32 bit float to work on it, and export to a 24 bit PCM with 8 bits of empty storage, but that doesn't mean it's no longer 16 bit resolution, but I guess it seems better to state that on a site like DIME.

If anyone posted a recording on etree making that claim they'd have to shut off the comments again to stop the flood of remarks calling BS.

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Offline jefflester

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Re: Portable DAT modded to 24-bit?
« Reply #7 on: June 06, 2020, 06:45:11 PM »
I'm thinking Craig's explanation is the most likely. One of his "industry" friends moded the deck with a 24-bit A/D chip and he therefore thinks the deck was recording 24-bits.
« Last Edit: June 06, 2020, 06:47:45 PM by jefflester »
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Offline Ozpeter

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Re: Portable DAT modded to 24-bit?
« Reply #8 on: June 06, 2020, 07:46:58 PM »
I'm sure that simply listening to the recording would be the way to tell whether it's 24 bits or not.

(I am of course joking).

Offline jerryfreak

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Re: Portable DAT modded to 24-bit?
« Reply #9 on: June 06, 2020, 08:22:09 PM »
I'm sure that simply listening to the recording would be the way to tell whether it's 24 bits or not.

(I am of course joking).

surprised he didnt release the 48kHz version, must be holding out with this obviously superior version.
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Offline DSatz

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Re: Portable DAT modded to 24-bit?
« Reply #10 on: June 10, 2020, 11:11:51 PM »
The DAT recording medium was 16 bits wide. Period. [see later reply below for an amendment to this statement ... --ds] By the time DAT was invented, all the record logic was in ICs that couldn't be modified by mortal beings. I am quite sure that this person was recording no more than 16 bits per sample.

Noise-shaping can reduce the APPARENT noise level of a 16-bit channel to some extent, but this is done by shifting noise upwards in frequency to where we are somewhat less sensitive to it--basically sweeping it under the rug. Given any fixed number of bits to work with, you can't increase the actual dynamic range across the entire frequency band; you can only rob Peter to pay Paul. But there fairly soon comes a point--which differs with different approaches and different listeners--past which any further shifting of the noise causes a tangible feeling of "something's not right"-ness about the sound.

Sony, with their "Super Bit-Mapping" approach, found that point to be about 10 dB. In retrospect, I think a lot of engineers wish that they could have limited themselves to, say, 6 dB instead. They had a professional and a consumer version of the scheme; the SBM-1 adapter for portable DAT recorders was of course the consumer-grade system. But even the professional system has a rather bad reputation in retrospect--I never worked with it personally, but the main complaint I've heard from other engineers was audible artifacts at very low signal levels, and of course once you've applied this processing, it's "baked in" to the signal and can't be undone. Other vendors' noise-shaping approaches seem to have held up better--Apogee as I recall was said to have a good one. But best of all is not to try to fool people's hearing, and to use straight linear PCM with a channel quiet enough to accommodate your program material.

--Back when the Sony PCM-F1 was a new thing, I used to record concerts in its 14-bit mode, which had better dropout protection but inadequate dithering. Since at that time there was no way to edit consumer digital recordings or to transfer their contents digitally to any other system, I knew that the next step was always going to be analog dubbing. So I used Dolby "A"-type noise reduction with the PCM-F1, which gave it nearly the dynamic range of 16-bit recording along with the increased dropout protection. There were even more powerful analog noise reduction systems (Dolby SR, telcom c4) which could have extended that range beyond the raw 16-bit level to some extent.

--best regards
« Last Edit: July 08, 2020, 12:31:20 PM by DSatz »
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Offline Ozpeter

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Re: Portable DAT modded to 24-bit?
« Reply #11 on: June 11, 2020, 08:29:38 AM »
I used to transfer F1/SLF-1 recordings to those big umatic cassettes for editing on a system that occupied a whole studio on its own, and editing was accomplished by going from one umatic tape to another, controlled by the system.  I used to use the facilities at HHB in their original premises at Scrubs Lane.  Actually the first CD I did is still around - see https://www.allmusic.com/album/bach-the-complete-partitas-mw0001808522 (the Partitas, not the other works).

I remember when I first went in there (at 60 pounds an hour...) the first thing I asked was where the headphone socket was so I could really hear what was going on. 

"You are only the second person to ask for that," said the HHB studio manager. 

"Oh, who was the first?"  I asked.

"Eric Clapton, just last week, when he came in to edit his new CD.  He sat right where you are."

"Wow - Eric Clapton sat in this chair?"

"He nearly shat in that chair when we told him how big a bill he'd run up."

I never tire of telling that anecdote, 36 years on... even when it's not exactly on topic.
« Last Edit: June 11, 2020, 08:37:12 AM by Ozpeter »

Offline H₂O

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Re: Portable DAT modded to 24-bit?
« Reply #12 on: June 13, 2020, 09:22:20 PM »
The Tascam DA-45HR is the only DAT machine capable of recording 24bit to DAT - I knew a taper that ran one at set shows - he ran 120 and 125m tapes to capture 2 hours per tape as the deck runs at 2x speed when recording 24bit - this was a rack mount deck and required AC power


The Sonosax Stelladat-II and the even rarer rack mount Sonosax DAT recorder are the only 4 track DAT recorders - they also run at 2x speed when recording 4 tracks


Pioneer made a number of 96khz DAT decks and again the run at 2x speed when recording 96khz


It would be nearly impossible to convert a standard 16bit DAT recorder to do 24bit - it would need to be completely redesigned and re-built

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Offline DSatz

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Re: Portable DAT modded to 24-bit?
« Reply #13 on: July 08, 2020, 12:42:41 PM »
Ah. Yes, there were non-standard DAT recorders that ran the tape faster (on a linear basis) to allow more bits and higher sampling frequencies. (https://www.soundonsound.com/reviews/tascam-da45hr and there were one or two others, besides). It was such a bad idea that I pushed it to the corner of my awareness back then, and thankfully forgot it until today when I was explaining to a younger person what a DAT was, and I noticed a reference in the Wikipedia article, and followed it up. Then the bad memory came back.

DAT, even in its standard form, is like ancient wax tablets; the miracle is not mainly in how well they work, but that they work at all after years of storage. I've just been transferring all my old DAT recordings to a pair of hard drives, and it's a good thing that I left nothing really crucial in this format without transferring it to CD-R fairly soon afterward. (Actually, a good number of these DATs were themselves transfers from PCM-F1 recordings on Beta II tapes; when I get around to those, I don't know whether anything will be salvageable at all.)

That said, in a few cases I have had entire tapes play through without audible errors. But they're not the majority by any means. Plus, for each tape I have to sit there with my headphones "glued on" for however long in order to know whether the transfer succeeded or not. Much of my working life was like that, years ago, though ... and it's very pleasant to listen now, without having to worry about the recording levels any more.

When a manufacturer makes a singular exception to a standard recording format, they become the sole source of support for that format. The chances are considerable that over time they will drop this support or go out of business--either of which leaves you stranded. The same thing is true in general of custom modifications to standard equipment--to make them worth the risks, they had better deliver more than a marginal improvement. That's generally more plausible in analog circuitry than in digital.
« Last Edit: July 08, 2020, 02:39:57 PM by DSatz »
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Offline jerryfreak

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Re: Portable DAT modded to 24-bit?
« Reply #14 on: July 08, 2020, 05:15:30 PM »
that’s strange, it must be a storage thing. almost all of my tapes from the 90s play as well as they did then

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Offline BradleyJY15

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Re: Portable DAT modded to 24-bit?
« Reply #15 on: July 08, 2020, 05:33:11 PM »
I transferred all my old DATs (that I care about) to hard drives maybe 3-5 years ago.  Tapes only dated back to 2000, so 15-18 years old.  I don't run any checks on them for errors, but i don't hear anything to tell me otherwise.  I always used Sony DDS tapes.  Not "Actual" DAT tapes.  Did any of you do that too?  I had read/heard back in the early 2000s that DDS tapes were made in a sterile environment, and DAT tapes were not.  And the DDS tapes were cheaper.
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Offline jerryfreak

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Re: Portable DAT modded to 24-bit?
« Reply #16 on: July 08, 2020, 05:56:20 PM »
I don’t think the manufacturing method of audio grade was any different than DDS. DDS were certainly cheaper and there’s a possibility they could’ve used higher grade tape but i’ve never seen any evidence of this.
most people used them because 90meter/3hoyr audio dats weren’t available
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