[KeithEmo]

There is a technical detail about the sample rate chosen for the Red Book CD standard that needs to be mentioned to put the choices made into historical context.

As has already been mentioned, in order to encode an analog signal without serious distortion, the analog signal MUST BE bandwidth limited to avoid the Nyquist frequency.
So, for example, if you're encoding audio at a 44.1k sample rate to put on a CD, you MUST pass that signal through a sharp low pass filter that eliminates all content above 22 kHz.
Likewise, when the signal is reconstructed, you MUST again pass the output through a sharp low pass filter that eliminates all aliases above 22 kHz.
If you wish to maintain a flat frequency response, and minimal phase shift and distortion below 20 kHz, this calls for a filter that is flat up to 20 kHz, but has 70 - 80 dB of attenuation at 22 kHz and above.
This poses a serious technical problem... because any filter with performance even approaching these requirements is very complex to design.
Even worse, in order to build such a filter, you must use components that are precisely the correct value, and some of them are very expensive.

Virtually all modern ADCs and DACs use oversampling...
Oversampling essentially uses a 'trick" to allow the use of a filter that is far more gradual.
(This simplifies the process of designing a filter that is flat to 20 kHz, yet still provides excellent attenuation of aliases, and can be produced for a reasonable cost.)

HOWEVER, oversampling technology was NOT yet developed when the Red Book standard was created.
And, without oversampling, the design criteria for the proper filter are so extreme that, as a result, most early equipment performed quite poorly (and equipment that performed well was extremely expensive).

Without oversampling, given the requirements for encoding and decoding signals "right up to the Nyquist frequency", there is a tradeoff:
- either use a somewhat gradual filter, and accept a high-frequency roll off that starts well below 20 kHz, as well as significant high frequency phase shift and significant aliasing distortion
- design a very complex filter, which is difficult and expensive to produce, and still introduces excessive phase ripple and other problems

Oversampling has essentially eliminated this issue entirely... which is why it is so widely used.
However, since oversampling wasn't available when the standard was created, it was a bad idea to set requirements for the standard that impose such a serious compromise.
(Even raising the sample rate from 44.1k to 48k, as was recommended by some engineers at the time, would have significantly relaxed the tradeoff between cost, complexity, and performance.)

ADC, not DAC. In DACs you have reconstruction filter which is a different thing.

Actually I said this in my #8. What I mean in #9 is that it would be stupid to bypass the filters.

 

[analogsurviver]

Where is that freaking love/adore button when needed !?!

 

[old tech]

HOWEVER, oversampling technology was NOT yet developed when the Red Book standard was created.

Oh yes it was, in fact Phillips proposed to use oversampling with 14 bit convertors back in 1978. Read the Phillips website I linked earlier.

 

[bigshot]

Redbook is already overkill.

 

[dprimary]

Oh yes it was, in fact Phillips proposed to use oversampling with 14 bit convertors back in 1978. Read the Phillips website I linked earlier.

My first CD player was a Phillips built with 4 times oversampling around 1982. If I remember right it was Magnavox branded in the US. Even then the oversampling players were regarded as better sounding, even though they had 14 bit convertors. I think the Sony PCM F1 was also 14 bit convertors which was the first digital recorder I used. Like most Sony recorders the sound quality was lacking, to be kind. The Sony 3324 was released soon after with equally horrid convertors and is likely the cause of much objections to digital. Luckily Apogee made replacement convertors for the 3324 and 3348 that sounded much better.

 

[dprimary]

My first CD player was a Phillips built with 4 times oversampling around 1982. If I remember right it was Magnavox branded in the US. Even then the oversampling players were regarded as better sounding, even though they had 14 bit convertors. I think the Sony PCM F1 was also 14 bit convertors which was the first digital recorder I used. Like most Sony recorders the sound quality was lacking, to be kind. The Sony 3324 was released soon after with equally horrid convertors and is likely the cause of much objections to digital. Luckily Apogee made replacement convertors for the 3324 and 3348 that sounded much better.

Meant Apogee filters not convertors, complete convertors was latter. Maybe mid 80's

 

[dprimary]

let's stop the strawman argument where you put the limitations of digital audio under a microscope while "forgetting" to look at the flaws of analogue media. pick your poison, analogue recording on tape, or vinyl, or whatever analogue medium you think is the right way, then we can actually put A and B side by side and discuss the level of fidelity coming out of such recording and playback media. spoiler, it won't make analogue recording look good.

There is not and never has been a lossless analog recording medium. When recording analog you had to spend time deciding your best compromise of trade off's for the recording you made. There is not a single piece of analog tape or vinyl the sounds anything like the the signal from the microphone(s). That doesn't mean it could not be manipulated into something pleasant but it was never accurate.

 

[old tech]

My first CD player was a Phillips built with 4 times oversampling around 1982. If I remember right it was Magnavox branded in the US. Even then the oversampling players were regarded as better sounding, even though they had 14 bit convertors. I think the Sony PCM F1 was also 14 bit convertors which was the first digital recorder I used. Like most Sony recorders the sound quality was lacking, to be kind. The Sony 3324 was released soon after with equally horrid convertors and is likely the cause of much objections to digital. Luckily Apogee made replacement convertors for the 3324 and 3348 that sounded much better.

Good info there.

My first CD player, a Pioneer Elite bought back in 1985 had a 16bit oversampling DAC, and that was a 1984 model. Oversampling DACs on consumer CD players were ubiquitous before then.

 

[old tech]

There is not and never has been a lossless analog recording medium. When recording analog you had to spend time deciding your best compromise of trade off's for the recording you made. There is not a single piece of analog tape or vinyl the sounds anything like the the signal from the microphone(s). That doesn't mean it could not be manipulated into something pleasant but it was never accurate.

It is not just the recording to tape and then playback that is compromised, to cut and playback a record more transducers are required and the lacquer master needs to be EQd (and EQd back again). Worse still, all these tweaks and EQs are done in analogue, further reducing the faithfulness of the original signal. The measurements clearly bare all this out.

 

[old tech]

Meant Apogee filters not convertors, complete convertors was latter. Maybe mid 80's

I recall Ludwig commenting about that. He was not overly impressed with his first foray into digital mastering until the Apogee filters came out around 1984/85. He then described it as sounding exactly the same as the sound he heard in the studio. He thought it was a remarkable achievement in audio progress as he had never before heard a final production sounding exactly like the source.

 

[analogsurviver]

There is not and never has been a lossless analog recording medium. When recording analog you had to spend time deciding your best compromise of trade off's for the recording you made. There is not a single piece of analog tape or vinyl the sounds anything like the the signal from the microphone(s). That doesn't mean it could not be manipulated into something pleasant but it was never accurate.

This digital love has to be put to some reasonable constraints - once and for all.

During the recent modo cleanups has been a post by somebody claiming analog never to have the dynamic range of RBCD. Whoever it was, I absolutely have to burst his overinflated digital bubble -

NO WAY ANY RBCD CAN EQUAL THE DYNAMIC RANGE OF THE BEST ANALOG COULD ACHIEVE .

Because RBCD is - theorethically - 96.xy dB dynamic range maximum - it can never be, even in theory, 97 dB or above.

As this is predominantely American forum, it is - expectedly - representing what is in best interest of american companies. So ,do not reply with a typical butt hurt reples to the following cold hard facts :

1. ) Analog tape AND record can benefit from decent noise reduction systems. And there was none better than

https://en.wikipedia.org/wiki/High_Com

Analog reel to reel recorder tape recorders with best tapes achive S/N around 80 dB... - add to that 20-25 dB noise reduction offered by Telcom C4 and you end up with 100 -105 dB dynamic range.

Even a notch or two below that, using Nakamichi High Com II ( HIGHLY modified - above all, Telefunken slopiness , which Nakamichi simply took over, without any corrections... ) and Technics RS-AZ 7 cassette deck can have dynamic range exceeding RBCD. If I could do it on kitchen table and using nothing fancier than a signal generator and analog oscillosope, on tight amateur budget, imagine what could be done provided sufficient finances have been available. RS-AZ 7 is a work of art even in stock form, from the circuit boards it is crystal clear they did have an even more advanced prototype version, and using electronic components advances made since its introduction, as one of the last serious cassette recorders, in 1996, makes one wonder what more could be achieved. Like it - or, believe it - or not, using lowest noise tapes ( BASF ) , this machine's ultimate S/N is limited by - HUM from the in-built power supply trransformers ... - and if I had any reasonable quantity of these silent tapes available, I swear I would have made the outboard power supplies for both the recorder and noise reduction units ( you need TWO Nakamichi High Com II's if you want monitor while recording - it works either in record (compand) or playback (expand) mode - can not do both at the same time).

It has to be admitted that even a single High Com II was rich back in the day - let alone two. and, consequently, few have been sold and even fewer have survived to this day - hence the cost.

Noise reduction can also be applied for analog records - not just tape. An, it has been - towards the very end as the main sound carrier. There were two main versions - dbx



and CBS's CX, a variant of High Com.DBX records could achive around 100 dB of dynamic rang .. - again, exceeding the dynamic rang of RBCD. Here the best video available online confirming this fact - made rather poorly, claiming only as being equal to CD, recorded with inferiour resolution of which Tascam DA-3000 DSD recorder is otherwise capable of - and all limitations of SQ on YT still apply :



CBS tried to do similar with CX, but failed royally - because of insistence it was COMPATIBLE also for listening without the CX decoder. iT WAS NOT... - and a single female singer loud enough to protest how her recording issued as CX encoded record played back on conventional record playback equipment without the CX decoder was enough to bury the effort. Similarly, most mastering engineers, whom I otherwise respect, failed to see the potential - and have been opposing CX with all four.



CX has been the brainchild of CBS Labs - https://en.wikipedia.org/wiki/CBS_Laboratories It has been a thorn in the heel of Sony during the introduction phase of the CD - because CBS Labs made each and every step necessary in order NOT to allow CDs to be copied digitallly, but devised a series of schemes that made sure copy could never be as good sounding as the original CD - in order to protect the contents, the enormous catalog of artists on CBS records. Soon enough, Sony had it with these supposed to be implemented limitations - and simply bought the whole sharebang. With a single stroke, got the contents for re-release as CD - and got to rid of the CBS Labs ASAP. Sony did NOT have a foresight enough what will happen with CD copying at first, internet second - in the future...

What Sony did, besides disbanding CBS Labs, was even less glamorous - they ORDERED BACK any CX encoded records still in stores - and see to that that they get destroyed. The threat of an analog record that has almost no more noise than a CD was considered too great a threat to the CD just being introduced to leave the things as they were at the takeover of the CBS. That is why today so few of these records remain... - and there are even cases where CBS itself has originally mixed up the record jackets/sleeves denoting CX record - it is, unfortunately, possible to get an ordinary record in a CX jacket... - and likely, though not yet encountered by myself, vice versa.

It is cruel that the best strings recorded prior to HiRez availabilility have been on - of all the recording artists, Julio Iglesias - of course on LP, CX encoded and reproduced trough CX decoder.

CX decoder ( again, the work of CBS Labs ) has been produced - EXACTLY to the schematics from the CBS Patent, to the last resistor and capacitor - by at least 3 companies - Phase Linear, CM Labs and Telefunken. It was - and is - to use the term by the member who is no longer on this thread - half-baked - IF I want to stay on the polite side.

I did not go trough the schematics of the Urei CX encoder .. .yet. I can only hope it is not of the same "quality" ...

Any analog recording within recent memory - say from 50 years ago towards the present - can exceed the 20 kHz limit for the frequency response of the RBCD. For nitpickers - 22050 Hz.

CONCLUSION: analog recording and playback can deliver the sound quality exceeding that of RBCD. Admittedly, at extreme care and expense - but I hope that above debunks, once and for all, that RBCD is inherently superior to any form analog.

It has never been and never will. It is merely a low(er) cost alternative of music delivery

 

[GearMe]

Aliasing isn't a real issue if it's done properly In one of the AES links in my sig file (I think the first one) there is a demonstration of exactly what aliasing does. There's an example you can download to hear aliased and unaliased samples of the same recording. Even though there is a difference between them, it's highly doubtful that it would be audible in any real world listening condition. Aliasing is just another way of "gilding the lily" so to speak. It isn't nearly as much of a significant factor as people who haven't taken the time to experiment with it seem to think it is.

Thanks, Bigshot...

Was hoping to steer the dialogue with SonyFan121 into a productive vein and get some sense of where s/he felt the discrepancies lie so we could talk about them in this type of manner.

TBH, I've been a 'transducers and mastering' are what really matters person for a long time

 

[GearMe]

This digital love has to be put to some reasonable constraints - once and for all.

During the recent modo cleanups has been a post by somebody claiming analog never to have the dynamic range of RBCD. Whoever it was, I absolutely have to burst his overinflated digital bubble -

NO WAY ANY RBCD CAN EQUAL THE DYNAMIC RANGE OF THE BEST ANALOG COULD ACHIEVE .

Because RBCD is - theorethically - 96.xy dB dynamic range maximum - it can never be, even in theory, 97 dB or above.

As this is predominantely American forum, it is - expectedly - representing what is in best interest of american companies. So ,do not reply with a typical butt hurt reples to the following cold hard facts :

1. ) Analog tape AND record can benefit from decent noise reduction systems. And there was none better than

https://en.wikipedia.org/wiki/High_Com

Analog reel to reel recorder tape recorders with best tapes achive S/N around 80 dB... - add to that 20-25 dB noise reduction offered by Telcom C4 and you end up with 100 -105 dB dynamic range.

Even a notch or two below that, using Nakamichi High Com II ( HIGHLY modified - above all, Telefunken slopiness , which Nakamichi simply took over, without any corrections... ) and Technics RS-AZ 7 cassette deck can have dynamic range exceeding RBCD. If I could do it on kitchen table and using nothing fancier than a signal generator and analog oscillosope, on tight amateur budget, imagine what could be done provided sufficient finances have been available. RS-AZ 7 is a work of art even in stock form, from the circuit boards it is crystal clear they did have an even more advanced prototype version, and using electronic components advances made since its introduction, as one of the last serious cassette recorders, in 1996, makes one wonder what more could be achieved. Like it - or, believe it - or not, using lowest noise tapes ( BASF ) , this machine's ultimate S/N is limited by - HUM from the in-built power supply trransformers ... - and if I had any reasonable quantity of these silent tapes available, I swear I would have made the outboard power supplies for both the recorder and noise reduction units ( you need TWO Nakamichi High Com II's if you want monitor while recording - it works either in record (compand) or playback (expand) mode - can not do both at the same time).

It has to be admitted that even a single High Com II was rich back in the day - let alone two. and, consequently, few have been sold and even fewer have survived to this day - hence the cost.

Noise reduction can also be applied for analog records - not just tape. An, it has been - towards the very end as the main sound carrier. There were two main versions - dbx



and CBS's CX, a variant of High Com.DBX records could achive around 100 dB of dynamic rang .. - again, exceeding the dynamic rang of RBCD. Here the best video available online confirming this fact - made rather poorly, claiming only as being equal to CD, recorded with inferiour resolution of which Tascam DA-3000 DSD recorder is otherwise capable of - and all limitations of SQ on YT still apply :



CBS tried to do similar with CX, but failed royally - because of insistence it was COMPATIBLE also for listening without the CX decoder. iT WAS NOT... - and a single female singer loud enough to protest how her recording issued as CX encoded record played back on conventional record playback equipment without the CX decoder was enough to bury the effort. Similarly, most mastering engineers, whom I otherwise respect, failed to see the potential - and have been opposing CX with all four.



CX has been the brainchild of CBS Labs - https://en.wikipedia.org/wiki/CBS_Laboratories It has been a thorn in the heel of Sony during the introduction phase of the CD - because CBS Labs made each and every step necessary in order NOT to allow CDs to be copied digitallly, but devised a series of schemes that made sure copy could never be as good sounding as the original CD - in order to protect the contents, the enormous catalog of artists on CBS records. Soon enough, Sony had it with these supposed to be implemented limitations - and simply bought the whole sharebang. With a single stroke, got the contents for re-release as CD - and got to rid of the CBS Labs ASAP. Sony did NOT have a foresight enough what will happen with CD copying at first, internet second - in the future...

What Sony did, besides disbanding CBS Labs, was even less glamorous - they ORDERED BACK any CX encoded records still in stores - and see to that that they get destroyed. The threat of an analog record that has almost no more noise than a CD was considered too great a threat to the CD just being introduced to leave the things as they were at the takeover of the CBS. That is why today so few of these records remain... - and there are even cases where CBS itself has originally mixed up the record jackets/sleeves denoting CX record - it is, unfortunately, possible to get an ordinary record in a CX jacket... - and likely, though not yet encountered by myself, vice versa.

It is cruel that the best strings recorded prior to HiRez availabilility have been on - of all the recording artists, Julio Iglesias - of course on LP, CX encoded and reproduced trough CX decoder.

CX decoder ( again, the work of CBS Labs ) has been produced - EXACTLY to the schematics from the CBS Patent, to the last resistor and capacitor - by at least 3 companies - Phase Linear, CM Labs and Telefunken. It was - and is - to use the term by the member who is no longer on this thread - half-baked - IF I want to stay on the polite side.

I did not go trough the schematics of the Urei CX encoder .. .yet. I can only hope it is not of the same "quality" ...

Any analog recording within recent memory - say from 50 years ago towards the present - can exceed the 20 kHz limit for the frequency response of the RBCD. For nitpickers - 22050 Hz.

CONCLUSION: analog recording and playback can deliver the sound quality exceeding that of RBCD. Admittedly, at extreme care and expense - but I hope that above debunks, once and for all, that RBCD is inherently superior to any form analog.

It has never been and never will. It is merely a low(er) cost alternative of music delivery

So...you're making an argument for Hi-Res Digital?

 

[KeithEmo]

Absolutely true.....

However, part of what created the "imbalance of perception" is the difficulty with producing vinyl recordings (for end users).

It's simple for most of us to make a digital copy of a vinyl album - and note the tiny differences between the recording and the original. However, it's not practical for most end users to make a vinyl copy of their favorite CD, and note the much larger differences. Therefore, because we can't make vinyl recordings ourselves, it's impossible to compare the differences that result from both processes... and many people come to think of vinyl albums as some sort of "reference" or "master" - rather than as just another copy (which they have no practical way to compare to the original).

This also brings up another interesting point. When the early tests were performed to determine whether "the CD format was audibly transparent".... they "inserted a CD quality A/D and D/A loop into the signal chain" to see if anyone could detect whether it caused audible degradation of the signal. However, was their signal source a direct feed from a high quality set of microphones and a mixing console, or was their source an ANALOG MASTER TAPE? (If their source was an analog master tape, then all they could really determine was whether the "CD quality signal loop" introduced WORSE signal degradation that that already being introduced by their tape equipment... and we already know that analog tape has many flaws and limitations. And, even if a direct feed from a mixing console, with live music, was used... the quality of their test signal was still limited by the quality of the console and other equipment they used. And their results were limited by the quality of the playback equipment they used... which presumes that whatever speakers and playback electronics they had available in the 1970s were also "audibly perfect".)

In simplest terms, all they could conceivably prove was that "the Red Book CD format was audibly transparent when reproducing the sample content they had available, and actually used, when they tested it". In other words, if you wish to claim that the tests that proved that the Red Book CD format was audibly transparent are still relevant, you must base that claim on the assumption that there is no content available today that is of audibly better quality than what was used when they ran the tests, and that there is no playback equipment available today that is audibly better than what they used. (If all they did was to prove that Red Book CD was audibly transparent when used to reproduced analog master tapes, which were themselves NOT audibly transparent, then you have not proven the wider case to be true.)

There is not and never has been a lossless analog recording medium. When recording analog you had to spend time deciding your best compromise of trade off's for the recording you made. There is not a single piece of analog tape or vinyl the sounds anything like the the signal from the microphone(s). That doesn't mean it could not be manipulated into something pleasant but it was never accurate.

 

[gregorio]

[1] There is a technical detail about the sample rate chosen for the Red Book CD standard that needs to be mentioned to put the choices made into historical context.
[2] HOWEVER, oversampling technology was NOT yet developed when the Red Book standard was created.
[2a] And, without oversampling, the design criteria for the proper filter are so extreme that, as a result, most early equipment performed quite poorly (and equipment that performed well was extremely expensive).
Without oversampling, given the requirements for encoding and decoding signals "right up to the Nyquist frequency", there is a tradeoff:
- either use a somewhat gradual filter, and accept a high-frequency roll off that starts well below 20 kHz, as well as significant high frequency phase shift and significant aliasing distortion
- design a very complex filter, which is difficult and expensive to produce, and still introduces excessive phase ripple and other problems.
[3] Oversampling has essentially eliminated this issue entirely...

1. Unfortunately, yet another typical KeithEmo post. Yes, the CD standard does need to be put into historical context but despite your statement, you have not put it into historical context, you've created a historical context that never actually existed in order to push your "filters" agenda again!

2. No CD technology was yet developed when the redbook standard was created because you obviously can't have a CD or CD player before you've created a standard that defines what CD actually is! HOWEVER, oversampling as a technology certainly was known about and it's use was envisaged.
2a. These statements are all true BUT ENTIRELY IRRELEVANT because despite your misinformation, oversampling was developed and ubiquitously employed by CD players by the time that CDs were launched to consumers. As far as I'm aware, ALL CD players, from launch day onwards, employed at least 2 times oversampling.

3. Great, now we're getting somewhere. According to the actual history (that ALL CD players had oversampling) and YOUR statement that "oversampling essentially eliminates this issue entirely", then logically you must agree that the "issue" you've raised never actually existed by the time CD was launched to the public (1983) and is therefore irrelevant!

Analog reel to reel recorder tape recorders with best tapes achive S/N around 80 dB... - add to that 20-25 dB noise reduction offered by Telcom C4 and you end up with 100 -105 dB dynamic range.

This statement is false. 80dB SNR + 20-25dB Noise reduction does NOT result in a dynamic range of 100-105dB!! This is a classic case of "cherry picking"; of only listing those facts which support an agenda while omitting the other pertinent facts which contradict it. The reality is that the original recording session tapes (with up to 80dB SNR) were OF COURSE, NEVER RELEASED TO THE PUBLIC. What was released was a several generation old copy: The recording session tapes would have to be edited, mixed (EQ, compression, etc.) and commonly "bounced down" (recording several tracks to 1 or 2 tracks), each of these mix processes adds noise. When the mix is complete it's bounced down to another (final mix) tape, for transfer to the mastering engineer, the mastering engineer applies analogue processing, which adds more noise, often bounces down during the mastering process and then when the mastering is complete, then bounces down the completed master to another (master) tape. Each of these bounce downs (generations/copies) doubles the amount of tape noise and there would have been an absolute minimum of 2 generations but probably 4 or more. Then, the master tape was copied to a production master and finally the distribution media (cassette or vinyl) was copied from the production master, so another two generations. That's a bucket load of noise that's been added between the original session recording tapes and the final media the consumer buys, so what that 20-25dB noise reduction (or more like 15dB in the more common NR types) actually achieves is some restoration of the 80dB SNR we may have started with.

In the best theoretical case, if we were just making a test tape, we could record a test signal to tape (with say 80dB SNR) apply say 25dB noise reduction and bounce down the result back to tape. That's 1 generation of SNR loss and therefore: 80dB SNR - approx 6dB generational loss + 25dB NR = a theoretical max of roughly 100dB DR. Of course though, we end up with just one test tape! We can only theoretically achieve this DR figure by eliminating all the: Editing, mixing, mastering, creation of a production master and the duplication of it to create the actual consumer product. In the real/practical world of commercial consumer audio recordings the actual equation is more like: 80dB SNR - approx 35-45dB generational loss and analogue processing noise + 15-25dB NR = a theoretical max of roughly 55-65dB DR, which is roughly 100 times less than analogsurvivor is claiming and why all his conclusions/assertions are complete nonsense! And of course, we're only considering noise and ignoring all the other non-linearities and distortions of analogue.

In this sub-forum we tend to focus the details of digital theory and it's implementation, however in the world of commercial recording studios and those who actually make the music products, the single greatest benefit and selling point of digital audio over analogue (which blew all other considerations out of the water), was the elimination of generational loss!

I recall Ludwig commenting about that. He was not overly impressed with his first foray into digital mastering until the Apogee filters came out around 1984/85. He then described it as sounding exactly the same as the sound he heard in the studio.

I'm not sure about the context of that quote. There really wasn't any digital mastering in 1985, it didn't become even a practical possibility until a decade later and it was almost another decade before the mastering tools had improved to the point that mastering in the digital domain became a viable alternative. Remember that contrary to popular belief, the SPARS code (AAD, DDD, etc.) did not refer to the domain of the procedures but the domain of what those procedures were recorded to. For example, if we record the musicians to digital recording media, mix it in the analogue domain then record that final (analogue) mix to digital, then master in the analogue domain and record the completed master to digital, the SPARS code would be "DDD" (even though it's been both mixed and mastered in the analogue domain). If we're talking about the actual processes, then with the exception of a very few classical recordings (a couple of labels had proprietary digital systems and minimal mixing and mastering), pretty much all recordings up to the mid/late 1990's should have been labelled DAA, then gradually DDA and finally, DDD would have started appearing in the early 2000's.

G