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#1
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Dolby A question
I recently acquired two 10 inch reels of 1/4 inch Grand Master 456 tape that
was recorded using Dolby A. I would like, after baking these reels to get rid of the sticky shed condition, transfer the music (pipe organ,of course) to CD. What can I use to decode the sound ? Do I need a Dolby A rack mount decoder or some other Dolby NR system that would work. Any help with this would be much appreciated. George |
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#2
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On Mon, 14 Feb 2005 16:42:55 -0800, "geoley" wrote:
I recently acquired two 10 inch reels of 1/4 inch Grand Master 456 tape that was recorded using Dolby A. I would like, after baking these reels to get rid of the sticky shed condition, transfer the music (pipe organ,of course) to CD. What can I use to decode the sound ? Do I need a Dolby A rack mount decoder or some other Dolby NR system that would work. Any help with this would be much appreciated. George Dollby A encode means you need Dolby A decode. Rick Ruskin Lion Dog Music - Seattle WA http://liondogmusic.com |
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#3
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geoley wrote:
Do I need a Dolby A rack mount decoder Yes. -- ha |
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#4
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geoley wrote:
I recently acquired two 10 inch reels of 1/4 inch Grand Master 456 tape that was recorded using Dolby A. I would like, after baking these reels to get rid of the sticky shed condition, transfer the music (pipe organ,of course) to CD. What can I use to decode the sound ? Do I need a Dolby A rack mount decoder or some other Dolby NR system that would work. Any help with this would be much appreciated. You need a Dolby A decoder. There's no way to do it in software yet. You may be able to rent one, or you might consider farming the job out to someone with a decoder. The things are frightfully temperamental and so I would be very suspicious of one picked up on the used market without having it gone over thoroughly. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
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#6
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geoley wrote: I recently acquired two 10 inch reels of 1/4 inch Grand Master 456 tape that was recorded using Dolby A. I would like, after baking these reels to get rid of the sticky shed condition, transfer the music (pipe organ,of course) to CD. What can I use to decode the sound ? Do I need a Dolby A rack mount decoder or some other Dolby NR system that would work. Any help with this would be much appreciated. George There is no reason why you should not copy the tapes to cdr before decoding the Dolby A. As you can easily make backup/safty cdrs without significant transfer degradation.Idealy you need to use a pro playback machine that offers the full range of line up adjustment. It is very important that you copy the Dolby ref and line up tones as without these decoding will be a very hit and miss affair. You can then send the CD to any facility with the dolby gear without risk and the expense of more tape. The only way to decode the Dolby A is with a Dolby A decoder. Steve Lane |
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#8
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"Charles Krug" wrote ...
That's surprising. Isn't Dolby A an dynamically adaptive filter with a more-or-less well-defined transfer function? But maybe there is no economically-viable market for a software Dolby decoder. Or maybe Dolby decided to not license such a thing. |
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#9
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On Tue, 15 Feb 2005 07:22:34 -0800, Richard Crowley
wrote: "Charles Krug" wrote ... That's surprising. Isn't Dolby A an dynamically adaptive filter with a more-or-less well-defined transfer function? But maybe there is no economically-viable market for a software Dolby decoder. Or maybe Dolby decided to not license such a thing. Oh possibly. I suppose if you have Dolby A tapes, you have the motivation to hire the codec, but otherwise it's just an odd filter that was popular twenty years ago. "You don't use Dubly for heavy metal . . " |
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#10
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wrote in message ups.com... geoley wrote: I recently acquired two 10 inch reels of 1/4 inch Grand Master 456 tape that was recorded using Dolby A. I would like, after baking these reels to get rid of the sticky shed condition, transfer the music (pipe organ,of course) to CD. What can I use to decode the sound ? Do I need a Dolby A rack mount decoder or some other Dolby NR system that would work. Any help with this would be much appreciated. George There is no reason why you should not copy the tapes to cdr before decoding the Dolby A. As you can easily make backup/safty cdrs without significant transfer degradation.Idealy you need to use a pro playback machine that offers the full range of line up adjustment. It is very important that you copy the Dolby ref and line up tones as without these decoding will be a very hit and miss affair. You can then send the CD to any facility with the dolby gear without risk and the expense of more tape. What would happen if the machine on which the tapes were recorded wasn't aligned properly? Asimuth, for example. Could it be fixed in software? Predrag |
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#11
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Charles Krug wrote:
On 15 Feb 2005 06:33:35 -0500, Mike Rivers wrote: In article rs.com writes: I would like, after baking these reels to get rid of the sticky shed condition, transfer the music (pipe organ,of course) to CD. What can I use to decode the sound ? Do I need a Dolby A rack mount decoder or some other Dolby NR system that would work. Yes, you need a real Dolby A system. There's no software plug-in substitute. Since this seems like a one-shot deal, you should look at renting one rather than buying one. That's surprising. Isn't Dolby A an dynamically adaptive filter with a more-or-less well-defined transfer function? Yes, and now that the patent has (fairly recently) expired, the threat of litigation is somewhat reduced as well. There is at least one person out there who has been modelling Dolby and dbx decoding systems using Matlab but he's not ready to publish yet or to make a commercial product. Maybe in a year. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
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#12
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wrote in message ups.com... geoley wrote: I recently acquired two 10 inch reels of 1/4 inch Grand Master 456 tape that was recorded using Dolby A. I would like, after baking these reels to get rid of the sticky shed condition, transfer the music (pipe organ,of course) to CD. What can I use to decode the sound ? Do I need a Dolby A rack mount decoder or some other Dolby NR system that would work. Any help with this would be much appreciated. George There is no reason why you should not copy the tapes to cdr before decoding the Dolby A. As you can easily make backup/safty cdrs without significant transfer degradation.Idealy you need to use a pro playback machine that offers the full range of line up adjustment. It is very important that you copy the Dolby ref and line up tones as without these decoding will be a very hit and miss affair. You can then send the CD to any facility with the dolby gear without risk and the expense of more tape. The only way to decode the Dolby A is with a Dolby A decoder. Steve Lane Steve: Thanks for your suggestion about transferring to CD after baking before decoding which is what I will wind up doing and again thanks to all who responded to my question. There is a little note attached to each reel that states to make sure to copy "the Dolby wobble tones with NR off". George George |
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#13
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"Predrag Trpkov" wrote in message ... wrote in message ups.com... geoley wrote: I recently acquired two 10 inch reels of 1/4 inch Grand Master 456 tape that was recorded using Dolby A. I would like, after baking these reels to get rid of the sticky shed condition, transfer the music (pipe organ,of course) to CD. What can I use to decode the sound ? Do I need a Dolby A rack mount decoder or some other Dolby NR system that would work. Any help with this would be much appreciated. George There is no reason why you should not copy the tapes to cdr before decoding the Dolby A. As you can easily make backup/safty cdrs without significant transfer degradation.Idealy you need to use a pro playback machine that offers the full range of line up adjustment. It is very important that you copy the Dolby ref and line up tones as without these decoding will be a very hit and miss affair. You can then send the CD to any facility with the dolby gear without risk and the expense of more tape. What would happen if the machine on which the tapes were recorded wasn't aligned properly? Asimuth, for example. Could it be fixed in software? Sorry, I meant the machine on which the tapes were played back. Predrag |
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#14
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Predrag Trpkov wrote:
What would happen if the machine on which the tapes were recorded wasn't aligned properly? Asimuth, for example. Could it be fixed in software? No. There _are_ some azimuth-compensating plug-ins, which allow you to delay one channel with respect to the other and apply an reverse-comb filter that is coupled to the delay. But the overall effect isn't all that good and the treble S/N is poor. It's much easier and better just to make sure the transcription is correct in the first place. And you _can_ make sure the transcription is good without having a Dolby decoder. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
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#15
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"Charles Krug" wrote in message That's surprising. Isn't Dolby A an dynamically adaptive filter with a more-or-less well-defined transfer function? Yes, but not a much so as SR ! geoff |
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#16
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"Richard Crowley" wrote in message ... "Charles Krug" wrote ... That's surprising. Isn't Dolby A an dynamically adaptive filter with a more-or-less well-defined transfer function? But maybe there is no economically-viable market for a software Dolby decoder. There sure is a market ! geoff |
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#17
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#18
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#19
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"Mike Rivers" wrote in message news:znr1108488549k@trad... In article writes: What would happen if the machine on which the tapes were recorded wasn't aligned properly? Asimuth, for example. Could it be fixed in software? Not as easily as fixing it in hardware. Simply align the playback machine to match the tape. It'll never get any better than that. Of course if you take the route that someone suggested of transferring the tapes to CD, you lose the opportunity to do that after the fact. Thanks. Yes, that's why I asked. It's tempting to do just that, especially in a hurry, relying on the notion that "you can do everything in software nowadays, you know". Predrag |
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#20
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Dolby A encode means you need Dolby A decode.
Unless you want it to sound like George Michael. (It works!) : ) V |
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#21
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#22
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#23
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#24
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In article znr1108488549k@trad, (Mike Rivers)
wrote: What would happen if the machine on which the tapes were recorded wasn't aligned properly? Asimuth, for example. Could it be fixed in software? Not as easily as fixing it in hardware. Simply align the playback machine to match the tape. It'll never get any better than that. Of course if you take the route that someone suggested of transferring the tapes to CD, you lose the opportunity to do that after the fact. And I have been told by a local tech who knows first hand, you can't string Dolby-A encoded audio over to CD then decode it; it just doesn't work right. Apparently you -have- to decode it first. -- Eric Frampton, keyboards Atlanta, Georgia, USA http://www.ericframpton.com (remove the year from the email address above to get my real address) |
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#25
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"Mike Rivers" wrote in message Of course if you take the route that someone suggested of transferring the tapes to CD, you lose the opportunity to do that after the fact. .....b ut you'd be silly not do do it when transcribing, as it's only a screwdriver-tweak away... geoff |
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#26
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"Predrag Trpkov" wrote in Thanks. Yes, that's why I asked. It's tempting to do just that, especially in a hurry, relying on the notion that "you can do everything in software nowadays, you know". You can't play a reel tape in software though, so one may as well do it properly when one do play it. geoff |
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#27
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"Eric Frampton" wrote in message And I have been told by a local tech who knows first hand, you can't string Dolby-A encoded audio over to CD then decode it; it just doesn't work right. Apparently you -have- to decode it first. Can he explain why ? geoff |
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#28
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Geoff Wood wrote:
"Eric Frampton" wrote in message And I have been told by a local tech who knows first hand, you can't string Dolby-A encoded audio over to CD then decode it; it just doesn't work right. Apparently you -have- to decode it first. Can he explain why ? Maybe some of the encode/decode info is above 22k. Can be done at 96k sampling rate? |
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#29
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"Joe Sensor" wrote in message Can he explain why ? Maybe some of the encode/decode info is above 22k. From tape ?!! Maybe he doesn't know as much as people believe he does. geoff |
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#30
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And I have been told by a local tech who knows first hand,
you can't string Dolby-A encoded audio over to CD then decode it; it just doesn't work right. Apparently you -have- to decode it first. The only semi-rational reason I can think of is that the non-constant group delay introduced by the filtering in the A/D and D/A conversion screws up the Dolby A processor's ability to correctly read the signal's average and peak levels. Of course, analog tape recorders introduce non-constant group delay because of HF spacing loss. And the filtering in digital filters can have constant group delay, if the designer so desires. This raises another issue... Remember how people used to say "Dolby [b] dulls the sound"? About 20 years ago, after buying two Nakamichi NR-200 Dolby B/C processors, I decided to test this. I hooked up a processor to encode and decode _without_ a tape recorder in the loop. (This eliminated a number of problems, including the claim that the dulling was a pyschoacoustic effect produced by suppressing tape hiss.) Levels -- both encode/decode and input/output -- were carefully matched. Switching the processor in and out, there was no question that Dolby B slightly dulled the sound. Wondering whether this was due to some unintentional misadjustment, I raised the playback level to the decoder by 1dB, then recalibrated for unity gain. It still dulled the sound. (The same test, with dbx II, did not dull the sound.) * Assuming this is a valid observation, I have a theory as to the reason. It has to do with an error in the design of Dolby B. The HF boost added by Dolby B necessarily increases the relative peak level of the signal. In order to keep the increased peaks from saturating the tape, the encoder includes peak clipping of the side-chain signal. Now, since the decoder uses a combination of peak and average detection, it follows that the decoder will see a lower playback level than it would if the signal weren't clipped. QED. In case the "error" isn't obvious -- why have the processor do something to the signal that the recorder is going to do anyway? And if improvements reduce or eliminate the problem, the NR processor adds asymmetrical processing that cannot be reversed. Of course, it just might be that the Dolby circuits are inherently a bit dull-sounding, and the dbx circuits aren't. * Arnie will object that these tests were not double-blind, let alone blind. If he'd care to stop by, I'd be happy to repeat them, at least blind. |
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#31
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In article ,
Joe Sensor wrote: Geoff Wood wrote: "Eric Frampton" wrote in message And I have been told by a local tech who knows first hand, you can't string Dolby-A encoded audio over to CD then decode it; it just doesn't work right. Apparently you -have- to decode it first. Can he explain why ? Maybe some of the encode/decode info is above 22k. Can be done at 96k sampling rate? No. Dolby A got used on a lot of machines where the response dropped off at 18 KC anyway. The real problems are with low frequency aberrations. If your tape has tones, I don't see any reason why you can't set for playback with flat tones and transfer through a digital generation and then back to decoder. If the tape does NOT have a full tone ladder and only has Dolby tone, however, you can't adjust the playback de-emphasis EQ properly. If you don't have the tone ladder, you have to adjust the de-emphasis by ear to get the lowest level of pumping. This is especially a big deal with the low-frequency control. This was, unfortunately, the case with a lot of Dolby tapes. Certainly all the ones I did... --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
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#32
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Geoff Wood wrote:
"Joe Sensor" wrote in message Can he explain why ? Maybe some of the encode/decode info is above 22k. From tape ?!! Tape reproduction certainly becomes non linear at that point, but that doesn't mean there is no signal there. I don't know anything about how Dolby A encoding works, so it was just a guess. Maybe he doesn't know as much as people believe he does. Who do you mean? |
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#33
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In article ,
"Geoff Wood" wrote: "Eric Frampton" wrote in message And I have been told by a local tech who knows first hand, you can't string Dolby-A encoded audio over to CD then decode it; it just doesn't work right. Apparently you -have- to decode it first. Can he explain why ? At the time, when I asked why, he basically said "just trust me". And I do, so I did. I haven't talked to him about it in years, but it'll be a good excuse to give him a call. He used to be the staff tech at Master Sound here in Atlanta, so I dare say he worked on his fair share of machines and Dolby racks... e -- Eric Frampton, keyboards Atlanta, Georgia, USA http://www.ericframpton.com (remove the year from the email address above to get my real address) |
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#34
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On Wed, 16 Feb 2005 10:59:02 -0500, Eric Frampton
wrote: Can he explain why ? At the time, when I asked why, he basically said "just trust me". And I do, so I did. Dolby A is just a multiband compander. There are no subsonic or supersonic control tones and all sidetrack signals must be derived from the audio tracks. That's why absolute levels are so critical. Chris Hornbeck |
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#35
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Chris Hornbeck wrote:
On Wed, 16 Feb 2005 10:59:02 -0500, Eric Frampton wrote: Can he explain why ? At the time, when I asked why, he basically said "just trust me". And I do, so I did. Dolby A is just a multiband compander. There are no subsonic or supersonic control tones and all sidetrack signals must be derived from the audio tracks. That's why absolute levels are so critical. It also makes flat response critical too. Which means that things that might screw the response up (like 1980s digital hardware, or tape machines with de-emphasis problems) are anathema. --scott -- "C'est un Nagra. C'est suisse, et tres, tres precis." |
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#36
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Geoff Wood wrote:
"Joe Sensor" wrote in message Maybe some of the encode/decode info is above 22k. From tape ?!! Without commenting on whether or not information above 22 KHz has anything to do with accurate Dolby A decoding, even my lowly (compared to an A80 and such) B67 was 3 dB down at 30 KHz for years. -- ha |
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#37
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#38
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"Joe Sensor" wrote in message Maybe he doesn't know as much as people believe he does. Who do you mean? Some way back in the thread a dude who was evidently credited with 'knowing' was quoted as stating that it couldn't possibly work. geoff |
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#39
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"Mike Rivers" wrote in message . If you record the CD at a conservative level and adjust the playback level so the Dolby tone puts the meters on the Dolby unit on the calibration line, there's no reason why it wouldn't work just fine. Or record your CD at full/whatever level, and set your correct level into the Dobly by (any) other means. geoff |
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