preview head or delay line

Discussion in 'Mastering' started by phaselag, May 1, 2007.

  1. phaselag

    phaselag Guest

    This is probably a question for someone who is actually involved in the mastering process of today’s analog pressings of LPs. The actual question is near the end of this post.

    First, I encountered many months ago a newsgroup article about the CBS Discomputer. The guy was saying that the CBS Great Performances classical remaster series (covers are tan with black text, like an old newspaper) were actually digital. I found this hard to believe since I had listened to them for years and was sure they were pure analog. The ambience is intact in these recordings. Digital cannot do this.

    After an extended period on the web I evidently encountered the patent number for the Discomputer and downloaded it. The patent, as I recall, is from 1979 and is probably for the Discomputer, although it doesn’t say it. It is a CBS patent for a computerized cutting control.

    The CBS patent diagram shows that there is no digital component in the path to the cutting head (preview head to lathe with nothing in between).

    The guy on the newsgroup was saying that many companies at some point starting using digital delay lines between the master tape and the cutting head. I suppose that they did this at the end of the analog era, probably to avoid replacing the preview heads on a pure analog tape machine. Most(or many) LPs made after 1980 sound digital. I went to extremes to find older copies of late reissues and there is a definite defference. The older issues have much more ambient information.

    When the heads wore out on the pure analog machines they would use a standard tape machine with one head. The pure analog signal fed the cutting control computer and a digital delay line fed the cutter head.

    My question is this: Do the original master issues that are sold today use a digital delay line for the cutting head? Or do they have tape machines with preview heads? I was told years ago that they actually obtain the original analog master from the vault. They put up a million dollar bond before they can take it with them.

    The few analog remasters that I have heard were not obviously analog. Acoustic Sounds sells a lot of them, about $30 each. There must be at least 10 companies that make them. Best Regards, Mark
     
  2. Zilla

    Zilla Active Member

    Each facility will be differently outfitted depending on equipment availability and cost factors. Also it depends on the source media from which you are cutting.

    I can say that at our studio we have all options. If we are cutting an original Blue Note, for example, the source will be analog tape. Therefore we use a transport with preview and program heads. But if the source is a 1630 master for CD manufacturing, the program and preview heads of a tape machine won't enter into the equation. You would be dealing with a digital source and is therefore logical and desirable to use a digital delay. If the source is an audio file, then you can set up a DAW with two pairs of outputs and simply offset the program output for the required delay. You then may avoid delay processing all together.
     
  3. phaselag

    phaselag Guest

    Zilla, Thank you for the informative reply. I assume that the preview heads are still in production, or at least available for maintainence. It is good to know that at least some of the pressings are pure analog. Blue Note is a very interesting company.

    Do you know if any form of tracing similation is used today to correlate the groove geometry to a specific playback tip radius? In other words, are your LPs best reproduced with as small a radius as possible? Thanks again, Mark :D
     
  4. Zilla

    Zilla Active Member

    Yes, preview heads can still be repaired and/or replaced. But that is just the tip of the iceberg. To implement analog preview/program cutting properly one also needs to double their whole mastering chain. The reason is because whatever processing you make to the program signal must also be applied to the preview channel. If you don't then the disc computer gets erroneous information and the cut is fouled. So you need dual stereo tape playback electronics, dual stereo signal path, dual-ganged stereo eq, dual-ganged stereo line amps, dual-ganged stereo faders, etc. This is an expensive and technically daunting scenario. Most facilities will opt for the more economic and practical digital delay solution and sacrifice some quality.
     
  5. phaselag

    phaselag Guest

    I was surprised to see you reply. I hope I don't wear you out with questions.

    Do you only master or do you also press records? If so, what label are you? Do you have a website?

    Is there one source of information about who does or doesn't use a delay line? I see what you mean about the expense of using a preview head.

    I bought a Moody Blues remaster from MFSL a few years ago. I heard that a family dispute brought MFSL down. I can't convince myself that it is pure analog. Did they use a delay line? I wouldn't be surprised if all of the MFSL used a delay line. They never sounded right to me. I have a 1972 Denon digital pressing using PCM (the name they used back then). It is the cleanest digital I have ever heard (unlike Soundstream). Possibly MFSL was using digital all along, the technology was around.

    I don't know what all goes on in the cutting computer. Seems like it would have mostly velocity related decisions to make. I don't think tracing simulation changes the velocity much, but I don't know that much about it.

    I am sure that RCA's Dynagroove used tracing simulation (also called predistortion and styus correlation), because they said so. If one doesn't use a conical styus on a Dynagroove then the harmonics are all messed up. As I understand it, tracing similation was put into the master (I supposed it would be called the cutting master...the stereo mix).

    Question: When you obtain a master tape from the vault is it the multi-track, or the stereo mix? Possibly, you are getting a master that is already simulated for a specific tip radius. (Explained below) I encountered a conversation on the web somewhere about how bad the Dynagroove (1964 to about 1969) remaster CDs sounded. I suspect that they are copying masters simulated for a conical stylus.

    I have found that most of the vinyl (of major all companies), even into the 1970s often sounds unstable with a line contact stylus. For example, background noises can be greatly diminished.

    The reason that I am interested in tracing simulation is because the better cartridges have a small tracing radius. It would be good to know that little or no tracing simulation is used in remasters so a line contact will give optimum playback results.

    I'm trying to be brief, but this is not a brief subject. Those who I have talked to in years past claimed that tracing simulation was a theory that was never put into practice. I am quite sure that they were wrong. They probably didn't know that it was incorporated into the cutting master.

    It makes a tremendous difference. In years past, when most stylii were conicals it was almost mandatory for acceptable sound quality, especially for radio stations that almost always used a conical until the CD came into play.

    Specifically, tracing simulation from a geometric standpoint cuts clearances so that the "pinch effect" at high groove velocities does not impart an undue vertical component to the stylus deflection.

    Aside from the vertical component, the harmonics generated by the difference in the dimensions in the cutting and playback stylii cause very noticeable distortions( mostly harmonic) unless the groove is simulated (predistorted) for a chosen playback tip radius.

    DG and Phillips didn't use much (they sound like they are set for a .3mil) simulation in their classicals in the 1970s. Playing them with a conical will reveal the distrotions that can occur. Thus, I have a reference point. Columbia Masterworks sound much better with a concical, as does RCA.

    I know this subject is a load on the brain.......I will wrap this up as quickly as possible.

    I found in a recording handbook in the library under the topic of tracing simulation that Columbia and RCA both used "to-and-fro" simulation. This is probably simulation that has one alteration as the stylus goes up and another alteration when it goes down. Two different geometric paths caused by the addition or subtraction of the linear velcity of the record (rpm).

    Anyhow, if I haven't totally taxed your time and patience, do you know if you or anyone else is still altering the groove for a tip radius? You may not know what it is. Most engineers that I have talked to (not very many) don't even think that it ever existed . I'm quite sure that it was used extensively.

    In case that you are not specifically familiar with the problem of tip radius, here is it. The groove is cut with a knife edge. The playback stylus contacts the groove, but not at the center of motion. The center of motion of the stylus is up inside the styus. The groove wall is cut (correlated) so that the difference in motion is subtracted from the signal. The substracted information is added back in at playback. A specific tip radius is required for complete reconstruction of the signal.

    I have never found anything about the electronics necessary for this alteration. The AES journal in the late 50s shows how unmanageable the equations are. They involve phase shifts.

    Any information will be greatly appreciated. Again, I hope all of the remasters don't use tracing simulation so that they can be optimized with a line contact.

    One last piece of history. Before Dynagroove, which was the first computerized cutting process, the tracing simulation was done by a "bucket brigade": a nickname for some sort of capacitor array that changed values about every inch toward the center. Before stereo, in the days of the 1-mil stylus, this was done primarily to compensate for "translation loss" of high frequencies as the linear groove velocity decreases. This loss was caused by the massive difference in cutting/playback path caused by the large tip radius.

    Best Regards, Mark





    8)
     
  6. Thomas W. Bethel

    Thomas W. Bethel Well-Known Member

    phaselag

    There are soooooooooooooo many variables in playback of analog LPs that I am not sure you could ever address all of them.

    There are so many things to think about - they include: condition of the record , the grove/stylus interface, the cartridge, the shape of the stylus, the tracking weight, the capacitance of the tone arm wiring, the preamp, the connectors between the cartridge and the head-shell, the connections between the head-shell and the arm, the geometry of the arm, the way the cartridge is mounted in the head-shell, the material the head shell and tone arm are made from, the flatness of the record, the amount of mold grain/pressing artifacts left in the groves, the shape of the cutting stylus, whether it was cut on a metal master or on an acetate disk, the quality of the preamp driving the power amp, the power amp, the speaker cable to the speakers and the speakers themselves not to mention the room acoustics of the listening room and finally the personal preference of the person doing the listening.

    There is no scientific way to graph or interpret the results of changes in anyone of these variables against all the others variables and I don't thing that even a CRAY computer would be able to deal with the list(s) of variables.

    Suggest you listen and enjoy and don't try and scientifically analyze what is going on

    Vinyl rules.
     
  7. Thomas W. Bethel

    Thomas W. Bethel Well-Known Member

    Double post deleted
     
  8. phaselag

    phaselag Guest

    Thomas, I agree about the variables, but I do not understand your last two statements.

    I am not conducting a scientific analysis in an attempt to write a two-mile long equation containing every conceivable variable in the audio reproduction process. Maximum enjoyment is the objective....better sound through knowledge. You mentioned groove/stylus interface.

    First, the major questions:

    (1) Do you use a preview head or a delay line in analog mastering?

    (2) Do you use pre-distortion (tracing simulation) in the cutter signal?

    I know that pre-distortion was used in past years, but it was developed before the small stylus radius was available in the marketplace.

    I found on the web last night that the Neumann lathe had a pre-distortion circuit on a card.

    As pertains to the “scientific” aspect of recording and playback, the slope of the waveform contains delicate and essential information that must be faithfully reproduced if one is to preserve fidelity.

    Both pre-distortion and the shape of the playback stylus greatly influence the slope of the waveform.

    As the years move on the master tapes will degrade to the point where we will either have to deal with a digital transcription, or resort to whatever vinyl has survived. Perhaps the digital methodology will progress in years to come, but I don’t expect it. The SACD is a massive improvement, but it doesn’t seem to be taking off sufficiently to replace to original format. I suspect that the majority of today’s “analog” remasters are really digital. Once the signal has been converted to numbers there is no way to rebuild the original waveform. The mid-70s DG, Phillips, etc. pressings may someday become expensive fine jewels. The superiority of the pure analog recordings is pronounced.

    Specifically, the digital converters cannot faithfully reconstruct the slope of the waveform, thus essential information is lost forever.

    For example, I have two copies of the same 1954 recording of Fritz Riener-Also Sprach Zarathustra. One is the MFSL pressing and the other is the RCA 1/2 speed master series. The RCA is superior: pure analog. The MFSL is choked down and has a tremendous loss of ambient information: there is a converter in there somewhere.

    I have achieved major improvements in fidelity through learning about groove geometry, circuitry, and pressing methodology.

    I have also begun to realize that some engineers did know a lot of the science and the superiority of their work is obvious in the sound of the product: speaking of pure analog.

    I was browzing the AESJ one day in the library. I recall seeing an article about digital that said that there is a 180-degree phase shift at 10KHz (starting the sweep at 20Hz). I never could find the article again. I don’t know much about digital, but possibly the pulses don’t combine in the center of their duration, but at the leading edge.

    Best Regards, Mark
     
  9. Gold

    Gold Active Member

    I think you may be confusing two aspects in disk recording. The CBS DisComputer is for conserving disk space allowing for higher levels and longer running time on sides. It has little impact on the audio. It's in the preview path.

    Tracing simulation as I undrstand it was very rarely used. The tracing simulator was standard in the Neumann SAL74. It was called the TAS74.
    It sounded good in theory but for it to give predictable results levels had to be kept low. These days most of them have been removed from the racks. I don't know about any other systems that were developed.
     
  10. phaselag

    phaselag Guest

    Thanks Paul, this is the type of information I am looking for. Yes, the DisComputer is for groove depth control, but they could have used a delay line. The whole recording system that used the DisComputer used a preview head, from what I have gathered. The lengths of my posts are mostly background information that hopefully someone will comment on.

    Good to have the the TAS74 number.

    The guestion now is who is using a tracing simulator?

    When you say that the levels have to be kept low I assume that there was an adjustment. Evidently, low levels meant setting it for say a .3-mil radius as opposed to a .6-mil.

    I have also, realized that any direct-to-disk recording is digital. It would have to be if it had a pitch control.

    What I am ultimately seeking is to know who makes pure analog remasters and whether they use tracing simulation. I want to hear a line-contact stylus reproduce a record without a simulated groove.

    I get a catalog in the mail with hundreds of allegedly analog remasters. They use an analog source and the final product is the analog groove, but the cutting signal is often digital.

    As point of reference, I have always been amazed at the engineering in some of the pop records of the late 60s. Example, the Johnny Mann singers on Liberty. Unfortunately, they are almost always worn out by a blasted sapphire stylus in a console. They are beautiful recordings and are obviously simulated for a large radius. If anyone every remasters these I wouldn't want to buy anything except pure analog, hopefully with no tracing simulation. The engineering in these records is excellent.

    There is also the issue of whether any masters were simulated. I read somewhere that the tape was where the simulation was, but now it appears that it was done by the cutting circuitry (except for possibly Dynagroove).

    Thanks again, Paul.. Best Regards, Mark
     
  11. Gold

    Gold Active Member

    All variable pitch and depth computers don't care how the signal arrives. Analog, digital, it doesn't matter. You should seperate that question out.

    I would venture to say that no one is using the tracing simulator although I don't (and can't) know for sure.

    Audio levels have nothing to do with the unmodulated groove depth. A microgroove stylus has a standard tip radius whether it is spherical or elliptical.

    I meant that audio levels must be kept low to avoid groove distortion that would be distorted again by the TAS. This is why no one used it. I have never used one. All this information is second hand...

    There are a few places that can do analog cutting. Whether or not it is done depends on the situation.
     
  12. phaselag

    phaselag Guest

    Paul said:
    All variable pitch and depth computers don't care how the signal arrives. Analog, digital, it doesn't matter. You should seperate that question out.

    (-----before replies)

    ----It is not the cutting computer signal that is the issue. It is the fact that when an analog master tape is used with a delay line the pure analog signal is wasted on the cutting computer.


    Paul said:
    I would venture to say that no one is using the tracing simulator although I don't (and can't) know for sure.


    -----this appears to be the consensus, but this has evidently been the consensus through past decades. Whenever I talked to someone in past years they usually said much the same. From the looks of pictures of pressing facilities is was a tedious labor situation in general. It is conceivable that that it was more of a job than an art to most involved. Employees may have never cared about what was actually going on.....sort of like flipping plastic burgers. I was told by an ex-Columbia employee that they ran the stampers long past the wear point, until they broke and fell on the floor.


    Paul said:
    Audio levels have nothing to do with the unmodulated groove depth. A microgroove stylus has a standard tip radius whether it is spherical or elliptical.

    ----I don't follow you here. If by standard tip radius you mean the industry standard, I was told by an engineer in the early 90s that he industry standard was (as I recall) .5-mil. If you are saying that it doesn't matter what the radius is, then I must disagree. The larger the radius the greater the tracing distortion. If you are talking about the .7-mil cross-section, then I see what you mean, but what does this have to do with tracing distortion?


    Paul said:
    I meant that audio levels must be kept low to avoid groove distortion that would be distorted again by the TAS. This is why no one used it. I have never used one. All this information is second hand...



    ------This coincides with what I have gathered in general about the circitry. That is, is causes about as many problems as it solves. Tracing distortion is a very complex situation. Solving it electronically is probably impossible, especially when the flexing of the vinyl is a major component. On the other hand, the RCA Dynagroove Stylus Correlator seemed to be quite accurate. The Shure M44-G is still in production. .7-mil at 2 grams. Dynagroove played with a conical has a very good sound, despite claims that it is the worst vinyl around.



    Paul said:
    There are a few places that can do analog cutting. Whether or not it is done depends on the situation.


    -----By analog cutting do you mean using a preview head? Any phonograph record is analog, regardless of whether the signal to the cutter is digital.

    Paul, do you use a preview head in your remastering? No one except the first poster has stated this. This is the primary issue.

    I will emphasize here that the elliptical stylus didn't become commercially available until 1964. Mono records were pressed until 1968 and mono 45s went well into the 70s. In 1972 70% of the FM radios were still mono. This is one of the reasons quadraphonic was such as mess, they were trying to make it mono-compatible for FM. The point here is that the playback technology in the 70s was still focused on the world of the conical stylus.

    Tracing simulation was probably heavily implemented despite what the consensus is. The reason being, they were trying to optimize the records for people's record players, mostly console and box phonos.

    The CD-4 quad format brought in the Shibata line-contact stylus. I read in RCA CD-4 technical literature that a problem with the CD-4 record was that the tracing simulation for the supersonics interfered with the audio band. The supersonic simulation is set for a .4 mil elliptical. Again, probably an attempt to make CD-4 compatible with the older world of the large radius.

    It is conceivable that the tracing simulation was in the cutting master tape. From what I have gathered from posts thus far it is essential that the cutting computer get the same information as the cutting head. Possibly, putting the signal on the tape worked out better. Possibly the Neumann circuit was excluded to use something better that only a few people knew about in the mastering room. Regardless of the actual sound, tracing simulation cuts clearances for the conical at high velocities. This keeps the pinch-effect of the groove from pushing the stylus up out of the groove. This was the world of the ceramic cartridge in the console changer. These cartridges were short on vertical compliance. Best Regards, Mark
     
  13. Gold

    Gold Active Member

    I was referring to the .7 mil playback stylus. In your previous posts it seems like you think the groove depth needs to be 'matched' to the playback stylus. I think microgroove was meant to hve a base depth of 1.8-2 mil. Very often grooves are cut deeper but the plaback stylus sits in the same part of the groove no matter what. I have seen some playback styli have problems in a very deep microgroove.


    I have a Studer A80VUMKII prelisten deck for this. I have only a few clients who want this and send in tapes that are prepared well enough to do it. They are not reissue clients. All of my reissue clients send me digital files. I don't use a delay. I use four outputs from the DAW.
     
  14. Zilla

    Zilla Active Member

    Mr. 'lag. I think that you can abandon you concerns about tracing sim. Nobody in my circle of engineers ever liked it and so never implemented it in their systems. This is decades back, of course. I would also guess that if such a system where even still installed somewhere, it would not be functional due to age.

    You may also relax about direct-to-disc recordings. All the projects I am familiar with where cut fixed-pitch.

    While it is true that digital delay used with analog source is a degradation, I would be careful to pin it as the scapegoat for an unsatisfying pressing. There are just so many more factors which have greater impact on final pressing quality. But what is so incredible about vinyl is that with all its imperfections and non-linearities, it still crushes digital mediums with regards to music delivery.
     
  15. Gold

    Gold Active Member

    BTW, I know of a stash of TAS units. Comes with full documentation. Cheap.
     
  16. phaselag

    phaselag Guest

    "Mr. 'lag. I think that you can abandon you concerns about tracing sim."

    Mr. Z-hole. You win, but don't think that I care about what you think. I was looking for objective engineering information. I learned again what I knew before. You are button-pushers 9-5. To anyone that actually sought to help me, I thank you, but I can't seem to drag information out of people who can't read.

    You got rid of me. Now you can sell your razzle-dazzle to suckers. I sure don't want it. Case closed. Mark
     
  17. Thomas W. Bethel

    Thomas W. Bethel Well-Known Member

    Phaselag,

    People on this forum have been more than nice.

    I am beginning to think you are a troll.

    You seem to be obsessed with certain things in cutting records and when people try to explain that they are no longer used or were used infrequently you get upset with them and start making uncalled for remarks about them.

    Your posts are long and rambling and although I have enjoyed reading them they seem to be somewhat of a forum for pushing your own agenda (what ever that agenda is)

    This is a forum for sharing knowledge and asking questions. When you step over the line and start trying to convince everyone of the notion that you are right and everyone else is wrong then I think you have gone too far.

    MTCW and FWIW
     

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