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Topic: Digital Delay: The little dirty secret of vinyl mastering (including AAA records (Read 1925 times) previous topic - next topic
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Digital Delay: The little dirty secret of vinyl mastering (including AAA records

https://www.youtube.com/watch?v=TOuQDMy__Qk

 :o  99.9% of all vinyl records from 1979 to today have a digital element to them.
"The lack of money is the root of all evil." - Mark Twain


Re: Digital Delay: The little dirty secret of vinyl mastering (including AAA records

Reply #2
Another very interesting video (in italian, so use autotranslated-subs) about vinyls vs CDs:
https://youtu.be/oli3OWIjA2g
Forward Agency NPO

In progress we (always) trust.

Re: Digital Delay: The little dirty secret of vinyl mastering (including AAA records

Reply #3
Waiter! I found some bits in my distorsion soup!

Re: Digital Delay: The little dirty secret of vinyl mastering (including AAA records

Reply #4
I think that's where the loudness war be began.

That sounds more like the 'loudness button' for vinyl.
"The lack of money is the root of all evil." - Mark Twain

Re: Digital Delay: The little dirty secret of vinyl mastering (including AAA records

Reply #5
That sounds more like the 'loudness button' for vinyl.
Well actually, it is very much the opposite.

You can increase volume up to a certain point for vinyl. If you go higher, the record might start to skip because the stylus flies out of the groove because of the potentially large swings. This has always been that way.

However, the maximum length of audio depends on the width of the groove. The width of the groove depends the volume: higher volume means wider groove. If you want a longer groove, you must place the grooves closer together, and you must reduce the volume.

This digital delay line (or a special reel-to-reel machine with 2 heads 2 seconds apart) allows the cutting lathe to adjust the groove width dynamically based on the volume that is coming 2 seconds later. To fit a relatively long piece of audio on one side with a fixed groove width, you had to lower the peak volume of the audio. That is possible with overall volume adjustment or using a compressor/limiter. With adjustable groove width, that is not necessary. So, if anything, this removed the need for a limiter/compressor or improved the signal-to-noise ratio in certain scenarios.
Music: sounds arranged such that they construct feelings.

Re: Digital Delay: The little dirty secret of vinyl mastering (including AAA records

Reply #6
I'm skeptical that this actually matters, even when I attempt to put myself in the shoes of an anti-digital audiophool.

Re: Digital Delay: The little dirty secret of vinyl mastering (including AAA records

Reply #7
The audio is digitized and then converted back to analog just before that signal being cut into a vinyl master. Sure, if the sampling rate and bit depth are high enough and the conversion is done properly, no problem. But for people rejecting the Nyquist–Shannon sampling theorem (for example, people thinking of the output of an ideal DAC as a staircase signal) this is a deal-breaker of course.
Music: sounds arranged such that they construct feelings.

Re: Digital Delay: The little dirty secret of vinyl mastering (including AAA records

Reply #8
Did he say 8-bit resolution in some cases???  Surely that would sound awful.
It's your privilege to disagree, but that doesn't make you right and me wrong.

Re: Digital Delay: The little dirty secret of vinyl mastering (including AAA records

Reply #9
Did he say 8-bit resolution in some cases???  Surely that would sound awful.
That's early Japan release.
"The lack of money is the root of all evil." - Mark Twain

Re: Digital Delay: The little dirty secret of vinyl mastering (including AAA records

Reply #10
I saw that video a few days ago, and there's something I'm not clear about, probably thanks to the audiophool edge of the speaker.
This automated volume control device: Is it really digitizing audio, manipulating it on the digital domain, than then converting it back to analog for the cutter... or is it a digitally controlled analog gain control? Don't get me wrong, I don't have any bets on this race, as I'm not an anti-digital AP that I should be worried about the analog "purity" of the signal path, but I'd say that, if it's the latter, then there's seems to be even less of a point, no matter how much of an AP you are.

Re: Digital Delay: The little dirty secret of vinyl mastering (including AAA records

Reply #11
Put very simply: in order to get as much audio on a side of vinyl as possible, the cutter must know the audio 2 seconds 'early'. So, it needs a feed of the audio at some point, and a feed of the audio 2 seconds ahead of that point.

With the ahead feed, it can adjust the groove spacing, to make sure grooves don't overlap. Without this, space would be wasted on silent sections.

This seems very simple, having two feeds of the same audio, delayed by 2 seconds. Turns out that is wasn't back then. It was possible to get a reel-to-reel machine with 2 playback heads and a lot of wheels to guide the tape for those 2 seconds. See for example this deck, a modified Studer A80:

As you can see, this gets complicated really fast.

So instead of doing this, a device known as a digital delay line was introduced in the mastering process as soon as the technology was ready. The only thing it does is digitize the audio, store it in memory for 2 seconds, and than convert it back to analog again.

Now the cutting lathe can be fed with 2 signals. The first signal is directly from the reel-to-reel machine, which is only used to adjust the groove spacing. The second signal is delayed two seconds, with the digital delay line, and is used to actually cut in the master.

Music: sounds arranged such that they construct feelings.

Re: Digital Delay: The little dirty secret of vinyl mastering (including AAA records

Reply #12
"Cutting Vinyl At Abbey Road", I link to the section about the "Lathe Groove Spacing Computer":
https://www.youtube.com/watch?v=rc2LA9kC-4U&t=361s
At 17:40 you will see the mechanism that pushes it inwards.

Oh, and
* 13:45 for the old-school version of "Shouting in the Datacenter"
* They do have a Studer A80 there too, but:
* digital source
 ;)

Re: Digital Delay: The little dirty secret of vinyl mastering (including AAA records

Reply #13
Did he say 8-bit resolution in some cases???  Surely that would sound awful.
That's early Japan release.
I realise that, but even so it should have sounded awful!

it needs a feed of the audio at some point, and a feed of the audio 2 seconds ahead of that point.
Actually 60/33⅓︎ = 1.8 seconds for a 33⅓︎ RPM LP.

It strikes me these engineers missed a trick.  The problem is to feed the main signal at original quality to the cutting head, and only a lesser quality signal is required for the head transport servo but in anticipation of the main signal.

My solution would be to generate a servo track as a preparation stage, on a spare tape track, by running the master tape backwards.  The delay line doesn't need to be top quality, so long as it preserves the dynamics, and when the master tape plus servo track is then played forwards the servo track will be ahead of the main track even though it is read from the same head.  Thus, only the servo track is subjected to any additional processing whatsoever, and the analogue mastering remains analogue throughout.
It's your privilege to disagree, but that doesn't make you right and me wrong.

Re: Digital Delay: The little dirty secret of vinyl mastering (including AAA records

Reply #14
Quote
it should have sounded awful!
Not necessarily. The Japanese engineers could have been playing with faster tape speeds to bring out more detail.
"The lack of money is the root of all evil." - Mark Twain

 

Re: Digital Delay: The little dirty secret of vinyl mastering (including AAA records

Reply #15
Did he say 8-bit resolution in some cases???  Surely that would sound awful.
That's early Japan release.
I realise that, but even so it should have sounded awful!

it needs a feed of the audio at some point, and a feed of the audio 2 seconds ahead of that point.
Actually 60/33⅓︎ = 1.8 seconds for a 33⅓︎ RPM LP.

It strikes me these engineers missed a trick.  The problem is to feed the main signal at original quality to the cutting head, and only a lesser quality signal is required for the head transport servo but in anticipation of the main signal.

My solution would be to generate a servo track as a preparation stage, on a spare tape track, by running the master tape backwards.  The delay line doesn't need to be top quality, so long as it preserves the dynamics, and when the master tape plus servo track is then played forwards the servo track will be ahead of the main track even though it is read from the same head.  Thus, only the servo track is subjected to any additional processing whatsoever, and the analogue mastering remains analogue throughout.


A few reasons why this wouldn’t work… the delay is different for different tape speeds as well as for different disc speeds. So if you “bake in” your delay to cut a 33… now you can’t cut a 45. Etc, etc.


The quality also does have to match the actual program material, to some extent, in order for the cutting computer to accurately model the waveform. This is why mastering consoles replicate their changes across 2 channels - whatever changes are made to the program signal still have to be made to the preview signal.


The use of digital delay lines was not as common as you think it might be - the bigger mastering studios could all afford to have a real preview-head playback deck on hand. Though occasionally there might still be a need to cut from a digital delay… say, an album master is provided as 14” 30 IPS reels due to album length and your primary preview machine will only accept a 10.5” reel… whoops!

Of course, anyone caring enough to do a vinyl release from tape in the first place knows much better now. I don’t know of any studio still using a DDL in their tape-based mastering chain within the last decade, and anyone with half a brain in their head would just transfer to digital first if it was between that or a DDL. It’s not 1991 anymore.

Re: Digital Delay: The little dirty secret of vinyl mastering (including AAA records

Reply #16
Years ago Arnold B. Krueger posted a 1979 magazine with a review of a digital delay system at that time. I cannot find Arnold's original post (perhaps not on HA) so here are some screenshots:
X
X
X
X

Re: Digital Delay: The little dirty secret of vinyl mastering (including AAA records

Reply #17
Interesting article, thank you.  It takes me back to when I was a digital engineer in the '80s, using micro-sequencers to coordinate the function of signalling systems.
It's your privilege to disagree, but that doesn't make you right and me wrong.

Re: Digital Delay: The little dirty secret of vinyl mastering (including AAA records

Reply #18
It just seems to me vinyl mastering was approached in a much more pragmatic and less 'fundamental' way. Digital was an up and coming, new technique, already in use for delay lines in effects, and they were marketing a (presumably very expensive) device of which the measurements showed it was an improvement over using a bespoke tape machine. Much less wow and flutter and easily adjustable for any tape speed. Masters could in fact run at higher tape speeds, improving quality! It all makes perfect sense.

But now, vinyl production is much more prone to scrutiny by purists and snobs, demanding as much (expensive) analog gear as possible, despite it objectively deteriorating quality.
Music: sounds arranged such that they construct feelings.

Re: Digital Delay: The little dirty secret of vinyl mastering (including AAA records

Reply #19
Did some research and found that IBM PC in 1981 supports up to 256KB of RAM and Apple II in 1977 supports up to 64KB. 2 seconds of CDDA quality delay plus OS and software would require about 384KB. The IBM 3420 tape drive released in 1970 can be as fast as 1250000 bytes per second at 200 IPS, and the construction and read/write mechanism of the drive is much more complicated than typical analog tape machines.

So I can imagine such a digital delay could be quite expensive at that time, about 512GB of RAM by today's standard? Though should still be cheaper than building a specialized analog tape machine.

The digital spectrum shown on the magazine has some obvious imaging artifacts, so the digitization step should have some aliasing as well, but probably fine for vinyl.