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Topic: Digital delay lines in vinyl factories? (Read 6276 times) previous topic - next topic
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Digital delay lines in vinyl factories?

Hello all.

I've been reading HA Wiki for some information, and I've found information about analog delay lines being replaced by digital ones during 70's in vinyl factories. And nothing more. I would like to know more, what are those exactly, I've searched the forum, but to be frank, finding specific information with digital and delay keywords here is... sometwhat impossible.

Any link, document where this is explained would be great.
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Re: Digital delay lines in vinyl factories?

Reply #1 –
In short: delay lines are a form of memory. That can be analog memory, or digital memory. Both kinds exist and both are (were) widely used.

I know of delay lines in three areas:

1. Music
Mechanical delay lines (often using springs, metal rods, etc.) were used to create echo and reverb.
Here's a picture: http://tor-johnson.com/newsoundlab/skin/frontend/default/blank/images/nsl009-04.jpg
A transducer (speaker) goes on one end, and a microphone on the other. Sending audio through that material essentially sends it on a detour through that material, creating a delay. Tape delay is another application, where you record and then play back that recording immediately after. The distance between the record and playback head creates a delay. The delay lines using coiled springs, etc. not only stored the signal, but also added resonance, etc. which sometimes was desired. Torsion wire delay lines were less susceptible to that, it works by using a Piezo crystal to twist the wire on one end, and use another Piezo crystal to turn that mechanical torsion back into an electrical signal. The length of wire itself and the material the wire was made of, acted as the body of material were that torsional twist was stored in, for a fraction of time.

2. Analog TV
To decode PAL color, every second line is inverted by 180° of phase shift, this ensures a better color stability (hence PAL: Phase alternating line). the previous line needs to be buffered to accurately create that phase shift.
Now we're talking much higher frequencies than audio here, but the principle is the same.
Here's a picture: https://en.wikipedia.org/wiki/Delay_line_memory#/media/File:Ultrasonicdelayline.jpg
This is a little crystal, with two transducers, one sends the signal into the crystal, the other one receives it on the other end of the path. Essentially that's analog memory. Since analog color TVs were very popular at some point, essentially everyone had one of those crystal delay lines in their homes.

3. Old computer memory
This is probably the most exciting one, and there have been some pretty outlandish implementations of this.
The idea is to store digital information for "a bit". When a bit is written into that memory, it lingers in the delay line for a fraction of time, and it is then read and immediately written back into the delay line. That's how it is possible to keep data in that memory technically indefinitely, as long as the machine is running.
Two of my favorite examples: Mercury delay lines: https://happidrome.wordpress.com/2009/08/04/forgotten-memory/ here's another one: https://en.wikipedia.org/wiki/Analog_delay_line#/media/File:FUJIC_delay_line_memory_1956_National_Museum_of_Nature_and_Science.jpg This works by having tubes filled with mercury and an electrode at either end. one is writing the bit, the other one is receiving it. The charge potential takes some time to reach the other end, that's where the delay comes in. The other example is a Williams Tube. This is a CRT, like in a TV or Oscilloscope.
The electron gun either paints a dot or not, encoding a one or zero. The phosphor on the CRT will have some afterglow, so the data can be read a fraction of time after it has been written. On the face of the CRT is an array of light detectors, these are used to read the data and return it to the electron gun circuit, but also allows to retrieve data that way. Here's a picture: https://en.wikipedia.org/wiki/Williams_tube#/media/File:Williams-tube.jpg
This is technology was one of the earliest methods of providing memory for computers. It was relatively simple, however the material cost and size was quite substantial. It was also very reliable. Early radar systems used that memory in things like the SAGE system to paint text and stored pictures on what was essentially radar screens.

Now here's the thing: Delay lines in vinyl factories? What exactly would they've been used for? I'm assuming they weren't used to buffer audio data, since vinyl records are pressed from a stamp, they're not cut each and every time. So, no idea where delay lines (which is essentially just memory) come into play in vinyl factories, but perhaps another member could shed some light on that.

Re: Digital delay lines in vinyl factories?

Reply #2 –
I've read about it, but I don't know how it was done.  The simplest method would have been tape delay.   You're cutting from a master tape so it would be fairly easy to add a 2nd tape head to read-ahead..

There was a hybrid analog/digital device called a bucket brigade device.  The analog signal was sampled (like digital) and the signal (amplitude) is stored as a charge (voltage).    A single memory "cell" stores one analog sample whereas 16-bit digital requires 16 memory cells plus analog-to-digital and digital-to-analog converters.

The major advantage of the bucket brigade device is lower cost (compared to a digital delay) and I doubt that would have been a big concern to the big record companies.

Quote
Now here's the thing: Delay lines in vinyl factories? What exactly would they've been used for?
They were used to adjust the spacing between grooves.   With quiet passages the grooves can be closer together and you can get more recording-time on the record.   With a delay, the lathe knows the loudness of what's coming in advance so the spacing can be adjusted in real-time to maximize overall (available) playing time.   It's sort-of like file compression...   You can put quieter sounds in a smaller physical space.

 

Re: Digital delay lines in vinyl factories?

Reply #3 –
The need for a "preview" of the audio being cut arose with the pitch computer which adjusted the groove pitch to allow for more lateral real estate for grooves with higher modulation levels.  It was initially accomplished by custom modifying a tape recorder's tape path to allow for enough tape between the preview head and the play head to provide delay equivalent to one record revolution.  And that's how it was done for years.  But no longer.

Lexicon invented the first practical digital audio delay unit in 1971, the "Delta T-101", but it had neither sufficient delay time nor audio specs to be used in mastering (60dB s/n, 10kHz bandwidth), so was relegated to sound reinforcement.  While specs improved with the next generation it took quite a while before memory costs and density improved enough to provide sufficient delay (just under 2 seconds), which at 44.1/16 PCM is almost 400K of RAM (4x 8-bit bytes).   Sounds like nothing now, but 1K was a lot back then, and fast memory was expensive.

But then,16 bit PCM wasn't exactly popular or affordable yet because ADCs and DACs didn't exist as monolithic solutions, they were custom made of massive numbers of individual parts, so there were other coding techniques such as "delta modulation" which were more practical, but they didn't perform well.  I recall several iterations of digital delay that were barely tolerable for sound reinforcement, and 200ms was a lot of delay. 

The analog "bucket brigade" devices introduced first invented in the early 1970s were CCDs (charge-coupled devices), where the analog input was sampled by storing it's instantaneous voltage in a capacitor, then clocking that charge through a chain of switches and capacitors and buffer amps with enough stages to provide useful delay.  Clock speed was completely arbitrary, but of course tied to both delay time and maximum frequency, as well as noise, which was pretty bad.  Decent audio BBD/CCD chips with lower distortion and noise, and higher stage count, didn't arrive until 1980 or so, and even then they were two chains of 512 stages...not enough for any significant delay at high enough clock speed for decent audio without cascading many, many chips.  They were useful only for effects and short delays, and were never used for mastering preview functions.

What really pushed mastering labs to digital preview was digital recording.   Recordings made or at least mastered any digital system created the need for a digital preview system.  A huge number of early digital recordings were made on a Sony PCM 1610/1630 system (U-matic video deck and 16/44 PCM converter) and needed a new form of delay because they never hit analog tape at all.  Sony introduced a mastering preview delay unit that took data from the PCM-1610 and clocked it through many, many memory chips, and out to a DAC, which drove the lathe.  The actual PCM-1610 DAC output would feed the lathe's pitch computer.  The system was lossless.  When memory and ADC/DAC technology matured (about the same time as the Sony device) other digital delays were introduced.  Once a digital preview system became more practical or economical than a custom modified tape recorder, they started to become common.  Consider that a 15ips master tape would require zig-zagging nearly 30" of tape between the preview and play heads without introducing additional flutter.  And 30ips tapes required almost 60" of tape to be somehow handled between preview and play.  Since mastering operations were a very small market segment for tape recorder manufacturers, a lot of these were custom jobs.  And that's where digital delay edged its way in.  You could use a standard tape machine without mods.  The bulk of records mastered between the late 1970s and the demise of vinyl were cut through a digital delay, even if they were analog recordings.  And that condition largely remains today.  A quick survey of mastering labs web sites showed mostly stock analog recorders, and no mention of analog preview.  In fact, after looking over about two dozen sites, I found only two with visible modified analog machines in their studio photos.  And none of the manufacturers of the machines in use are making machines today.  The Ampex ATR-100 is popular (unmodified), but I found a lab using a modified MCI machine, and another using a modified Studer A-80.  What that tells us is, to achieve the preview function, mastering labs are almost universally cutting through a digital delay.

One more note on analog delay.  The mechanical "delay lines" mentioned earlier were actually misnamed.  The actual time delay to the first arrival was relatively short, because the metal springs or plates/sheets transmit sound faster than air, but because the also resonated and bounced internal reflections around a semblance of reverb could be achieved, but not delay.  In the later days of springs and plates digital delays were inserted ahead of them as a pre-delay, making them more realistic. 

Re: Digital delay lines in vinyl factories?

Reply #4 –
Quote from: polemon on
In short: delay lines are a form of memory. That can be analog memory, or digital memory. Both kinds exist and both are (were) widely used.

I know of delay lines in three areas:


Another fairly common use is in (analogue) oscilloscopes. The trace can't be seen for an event that caused the trace to trigger unless the signal is slightly deayed, since the trigger circuitry takes finite time to start the sweep and the event would have passed. Not applicable to audio recording, so somewhat OT.

Re: Digital delay lines in vinyl factories?

Reply #5 –
Quote from: antz on

Another fairly common use is in (analogue) oscilloscopes. The trace can't be seen for an event that caused the trace to trigger unless the signal is slightly deayed, since the trigger circuitry takes finite time to start the sweep and the event would have passed. Not applicable to audio recording, so somewhat OT.

Analog scopes don't delay the signal, they delay the sweep trigger.  Simple timing, not signal delay.

Re: Digital delay lines in vinyl factories?

Reply #6 –
Quote from: DVDdoug on
I've read about it, but I don't know how it was done.  The simplest method would have been tape delay.   You're cutting from a master tape so it would be fairly easy to add a 2nd tape head to read-ahead...

That's exactly how it was done back in the day. There were dedicated mastering tape machines with two playback heads. A few of them are still in use, but i assume you'll have to pay a premium price for the effort (not that it would make an audible difference anyway...). One example definitely mastered the oldschool way are the Mission Of Burma reissues on Matador Records a few years ago. There was a short "making of"-video where they show the machine in action.

Kinda makes you scratch your head when audiophoolia-victims try to make a point about vinyl's supposed superiority because of analog master tapes being used. When in practice there's a rather slim chance those original tapes were used instead of a digital master file. And even if they actually went back to the analog tapes, chances are even smaller they didn't use a digital delay line. Most likely there was digital audio used somewhere in the mastering chain, and as far as i know it's been that way since the late seventies/early eighties. It made the engineers' jobs a bit less of a headache.

Re: Digital delay lines in vinyl factories?

Reply #7 –
Quote from: dc2bluelight on
Quote from: antz on

Another fairly common use is in (analogue) oscilloscopes. The trace can't be seen for an event that caused the trace to trigger unless the signal is slightly deayed, since the trigger circuitry takes finite time to start the sweep and the event would have passed. Not applicable to audio recording, so somewhat OT.

Analog scopes don't delay the signal, they delay the sweep trigger.  Simple timing, not signal delay.
Well according to this site they do:
http://w140.com/tekwiki/wiki/Delay_line

I did recently dispose of an old, valve-based (tube-based to anyone in the U.S.) scope from the 1960s. It was a dual-beam scope (i.e. 2, separate guns) and contained dual vertical amplifiers, each having its own, lumped-circuit, delay line.

However, this is rather OT and nowt to do with vinyl recording.

Re: Digital delay lines in vinyl factories?

Reply #8 –
Quote from: antz on
Quote from: dc2bluelight on
Quote from: antz on

Another fairly common use is in (analogue) oscilloscopes. The trace can't be seen for an event that caused the trace to trigger unless the signal is slightly deayed, since the trigger circuitry takes finite time to start the sweep and the event would have passed. Not applicable to audio recording, so somewhat OT.

Analog scopes don't delay the signal, they delay the sweep trigger.  Simple timing, not signal delay.
Well according to this site they do:
http://w140.com/tekwiki/wiki/Delay_line

I did recently dispose of an old, valve-based (tube-based to anyone in the U.S.) scope from the 1960s. It was a dual-beam scope (i.e. 2, separate guns) and contained dual vertical amplifiers, each having its own, lumped-circuit, delay line.

However, this is rather OT and nowt to do with vinyl recording.
Yeah, just a bit OT.  To start with they were looking for 60ns of delay.  And the did it with 51' of coax.  Not at all the same thing as an audio delay of 1.8 seconds!

Re: Digital delay lines in vinyl factories?

Reply #10 –
Quote from: dc2bluelight on
The need for a "preview" of the audio being cut arose with the pitch computer which adjusted the groove pitch to allow for more lateral real estate for grooves with higher modulation levels.  It was initially accomplished by custom modifying a tape recorder's tape path to allow for enough tape between the preview head and the play head to provide delay equivalent to one record revolution.  And that's how it was done for years.  But no longer.
Ah, thanks! thank makes total sense!
Quote from: dc2bluelight on
One more note on analog delay.  The mechanical "delay lines" mentioned earlier were actually misnamed.  The actual time delay to the first arrival was relatively short, because the metal springs or plates/sheets transmit sound faster than air, but because the also resonated and bounced internal reflections around a semblance of reverb could be achieved, but not delay.  In the later days of springs and plates digital delays were inserted ahead of them as a pre-delay, making them more realistic. 
That's right, but torsional mechanical delay lines were still used as a form of memory. They were used in very old HP desk calculators, the size of a typewriter. However the delay lines in things like spring "delay lines" were actually used as a form of "spring reverb", and I remember them being labeled as such, too - although not very often.
And of course solids have a much higher speed of sound that liquids, let alone gases.

Btw. in a documentary about the BBC radiophonic workshop, they shown how some of the musicians used a violin bow on some of the various "delay lines" (mech. reverb coils) to create special effects.