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Since its inception ten years ago, the Harbeth User Group's ambition has been to create a lasting knowledge archive. Knowledge is based on facts and observations. Knowledge is timeless. Knowledge is human independent and replicatable. However, we live in new world where thanks to social media, 'facts' have become flexible and personal. HUG operates in that real world.

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Early analogue recordings & an evaluation of analogue technology ...

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  • #16
    I like paintings and photos too!

    Alan

    Excellent comparison! I utilize both mediums, records for nostaligia (and listening to recordings that are not yet available digitally), and the requirement to pay attention to what is playing, one does have to turn the record over...and digital for ease of use, usually through an internet radio station. However, I purchase much over the 'net and will sit and pay attention to it, as I purchased it specifically to hear and listen. Is there one medium prefered to the other...depends on the recording for starters, however, is one medium better than the other...nope.

    I like listening to music and if its on vinyl, and I want to listen to it, then the Oracle Delphi gets cranked up, digital, then the Wadia and the DAC. I like paintings and I take photographs too.

    cheers

    George

    Comment


    • #17
      The last word in analogue tape technology

      Well, I couldn't resist dusting down the studer A807 which lives at the Old Barn. Delightfully, it's still working. Perhaps over the next few days I can show you what this carefully aligned (40kg?) beastie is technically capable of?

      Picture of my A807. Underneath on trolly shelf is Dolby 363 SR record/replay module - the final development on the Dolby A, B, C, S, SR noise reduction line that made analogue tape's hiss limitations bearable. As new this pair probably cost at least 20,000. It's probably technically outperfomed by a 50 MP3 recorder/player. Oh well, 'that's progress for you'.

      P.S Example of print-through found and will explain later.

      >
      Attached Files
      Alan A. Shaw
      Designer, owner
      Harbeth Audio UK

      Comment


      • #18
        Analogue anomalies - Part 1 ... a demonstration of the limitations of analogue media

        OK, to continue this exploration of the reality behind analogue and digital technology with one of my 'don't believe me, hear it for yourself' screencasts.

        The point I want to explore is one of the inescapable challenges for analogue tape, since it's very inception at the end of WW2. Namely, print-through. We should remember that recording tape is nothing more than one very, very long magnet. If we could store it without winding in onto a spool, tape print through wouldn't be a problem but keeping the tape crinkle free and not stretching it would be an insurmountable problem. So, tape has to be wound, and wound tightly so that one layer is intimately in contact with adjacent layers with nothing in between them to separate them. If it were possible to space the layers apart, even by the thickness of a sheet of paper the print through problem would greatly diminish. That's because the magnetic field on the tape is weak and by the time it had penetrated the paper spacer, it would be much diminished and have little impact on adjacent layers. But as it is, a 10.5" NAB reel - see the ones on my Studer A807 - using thick "low print through" standard-play tape can only hold about 32mins of audio, which means several reels and well judged reel swap-overs would be necessary to record a concert.

        So, even if we double the thickness of the already thin tape (to use the tape as it's own spacer as the magnetic oxide is on one side of the tape only) we'd reduce the recording time to around 15 minutes .... far too low to be of practical use recording a classical piece. So that's a non-starter. Or make the reels bigger? Then they're becoming difficult to handle and the inertia of the extra heavy reel spinning around during rewind needs a really big motor ... and that may have poor wow and flutter stability. So, as with so many audio issues, we are trapped between convenience, costs and performance.

        I'd like to present a cassette mastered for me at BBC World Service in 1989, with Brian Empringham reading the news and I bought-out the performance copyright from him. This was recorded live, directly off the U87, through the desk and to 1/4inch tape and cassette. The cassette machine was Studer, probably the finest ever made. The tape has not been played for at least 15 years, and was stored rewound at the beginning.

        First to set the scene play this short clip ....

        Loading the player ...


        Now for a technical analysis of that clip >>> here <<<.

        It is true that cassette tape is thinner than 1/4 SP recording tape and therefore the pre or post echo may be more apparent, but the magnetic flux is also smaller too. Do remember too, that every time the tape is played and then rewound due it stretch and slipping between layers the music content of adjacent layer will not ever be the same. So the print-through will add a degree of audio randomness which were the tape wound and rewound enough times would turn the pre and post echo into white noise. And as we know, noise is noise. Nothing useful can be retrieved below the noise floor.

        So I think we are safe to use this as a generic example of just one of the many limitations of analogue recording. As this shows, from the instant the tape passes over the record head, it degenerates. And therefore analogue tape fails the fundamental requirement for a high fidelity medium which is permanence.

        P.S. Remember the 70s and 80s when folks were laying out small fortunes for really sophisticated logic-controlled, all-singing all-dancing cassette decks and the marketing hype that accompanied them? Yes, the audio cassette and all its unique tape formulations was promoted as the serious-man's ultimate high-fidelity system, better than LP and without all those nasty clicks and plops. Scans of advertising material from the period to follow.
        Alan A. Shaw
        Designer, owner
        Harbeth Audio UK

        Comment


        • #19
          Direct to disk recordings

          Really finding this discussion enlightening - thanks.

          A question: I recall that a small number of recordings available on vinyl were recorded "direct to disc" - i.e. straight to the cutting head, bypassing tape entirely. As an analog medium, does this potentially offer greater fidelity to the original than magnetic tape with all of its inherent issues, including print-through?

          Comment


          • #20
            Direct to disc

            Originally posted by EricW View Post
            Really finding this discussion enlightening - thanks.

            A question: I recall that a small number of recordings available on vinyl were recorded "direct to disc" - i.e. straight to the cutting head, bypassing tape entirely. As an analog medium, does this potentially offer greater fidelity to the original than magnetic tape with all of its inherent issues, including print-through?
            Logically it should Eric. I have a few direct to disc & direct cut LPs & they mostly sound more dynamic, transparent & detailed than ordinary LPs.

            Comment


            • #21
              Originally posted by EricW View Post
              ... A question: I recall that a small number of recordings available on vinyl were recorded "direct to disc" - i.e. straight to the cutting head, bypassing tape entirely. As an analog medium, does this potentially offer greater fidelity to the original than magnetic tape with all of its inherent issues, including print-through?
              Thanks for the feedback. I frequently suspect that I'm talking to myself. Not a problem in itself because the value of this material can only appreciate with time and long after I'm pushing up the daisies!

              Yes I do recall the direct-to-disc (or more accurately, direct to disc stamping master) and the (then) fantastic fidelity of Thelma Houston's Pressure Cooker from Sheffield lab which I still have. It's hard to appreciate just how much care and attention was needed from the musicians to the mastering engineer to squeeze just a fraction more performance from the analogue recording chain. But even Sheffied Lab embraced digital when it arrived, which tells its own story I guess.

              The answer to your question (about tape print through) is tantalisingly within your own grasp. Can you ascribe a name to the mechanical equivalent of tape print through in the medium of the gramophone record? It's fundamentally the same problem: information from one rotation potentially bleeding through and corrupting adjacent ones.

              Im not sure if I made it absolutely clear in my demonstration in post #18 why this print-through is such a crisis (amongst a list of others were going to look at) for analogue tape. You may have the impression that the print-through only effects the gaps between the words (or music) as I demonstrated. That's not at all true. The print-through is audibly revealed when the wanted signal drops in loudness - i.e. the wanted signal ceases to mask the pre-echo (in my example). In fact, the amount of pre or post echo is constant throughout and 'underneath' the wanted audio, We can't hear it because it is masked, but it's definitely there, as a fidelity-robbing continuous drone. It, like other technical characteristics of the analogue system 'softens' the wanted audio just as viewing an oil painting under subdued rather than natural light hides belmishes. But it is takes us away from a faithful representation of the sound waves that hit the microphones.

              We've hardly started on the long list of Analogue Anomolies which were sidestepped at a stroke when digital arrived. There are so many techical oddities of analogue to demonstrate I just don't know which to turn to next.
              Alan A. Shaw
              Designer, owner
              Harbeth Audio UK

              Comment


              • #22
                Talking to Yourself? No way!

                Originally posted by A.S. View Post
                Thanks for the feedback. I frequently suspect that I'm talking to myself. Not a problem in itself because the value of this material can only appreciate with time and long after I'm pushing up the daisies!
                Alan, you should know that many of us read your posts with deep appreciation for the time you put into them and the manifold insights they contain. At the same time, we may not reply, because we don't know enough to make an intelligent contribution. Every morning I check for new posts in the HUG, and I'm especially delighted when I see your initials A.S. So never think that you are talking to yourself, but rather that you have a very full class of fascinated students, only a few of whom are raising their hands to speak.

                This is, in any case, how I choose to interpret any lack of interaction in my own classes!

                Bruce

                Comment


                • #23
                  The video talks etc.

                  Kind of you to say so. I'm not seeking parise and glory but it would be nice to know occasionally whether what I'm saying is appropriate, logical an above all else delivered at a pace which leaves a lasting impression with the reader/viewer. In particular, by far the quickest way for me to 'knock-up' a "tutorial" (big quotes) is to use the new video screen-cam software. It has the one big advantage to me that recording time is strictly limited to five minutes with a very small countdown timer in my screen that's easy to miss. I've been down to the last few seconds of recording time and have had to rush a bit to avoid a lock-up and need to re-record the lot. Five minutes duration means I have to get the point across at a pace which leaves no time to go into much detail - that may or may not be a plus. I aim to do a half-take just to check recording levels etc. and then to proceed with an unscripted one-take. In fact, even if it were rehearsed, with only five minutes available you can't take your eye off the screen to read a script, and there is no editing facility: what you see is in effect delayed live.

                  Ok, you prompted me to plan the next video and again that's on analogue tape's limitations. I've spent an hour experimenting with how best to convey this and the technical results are worse than I feared. At a stroke it explains why some listeners prefer the so-called 'easy' sound of analogue. But as we'll see, it's just another illusion. A pleasant one some say, but I don't think that you can argue with the audio analyser's display. What's interesting is that if you listen to the off-tape sound for a while, and then switch over to the perfect source, it is a bit of a shock to the ears. The digitally perfect source signal sounds rather cold, hard and with cleanly etched 'edges'. The off-tape analogue interpretation of the source has the edges sandpapered smooth and demands less attention.

                  I need to order some simple parts to be able to adjust the levels going into the tape recorder for a level-perfect comparison with what comes out, off tape. I'll do that over the next few days.
                  Alan A. Shaw
                  Designer, owner
                  Harbeth Audio UK

                  Comment


                  • #24
                    Knowledge free

                    I agree with Bruce (Euler). Not seeking to stroke or flatter, but I genuinely think I've learned more about audio from the HUG, particularly Alan's posts, than I have from any other source. I truly appreciate the time and effort Alan puts in.

                    Above all else, I think I've developed a much better appreciation of the difference between facts and marketing.

                    Comment


                    • #25
                      Roundabouts and swings and print through

                      Originally posted by A.S. View Post
                      ...the long list of Analogue Anomalies which were sidestepped at a stroke when digital arrived.
                      Print through....the fault that dare not speak its name. The final ten years or so of analogue dominance was a game of roundabouts and swings. When recording, it was always level and noise versus distortion, but the unspoken enemy that always showed itself when a big dynamic change came along was print-through.

                      Paradoxically, print-through became more of a problem with the arrival of a new generation of lower noise tapes in the seventies because the reduced noise floor showed up print-through that would previously have been masked by tape noise. The transfer function of print through was linear with changing level, that is to say a 10dB increase in recorded level would result in a 10dB increase in print-through although not all frequencies 'print' equally. Sadly, the worst frequency for print-through was typically smack in the middle of the human voice range.

                      This is the principal reason that tapes in long term storage are kept tail out. Print-through is worse in outer layers than inner layers because, to be audible, the printing source signal must reach the top of the oxide on the adjacent layer of tape. To reach the top of the oxide in an outer layer, the printing signal need only pass through the backing material; to reach the top of the oxide in an inner layer, it must pass through both the backing material and the complete oxide thickness. Because pre-print is subjectively worse than post-print, tapes are stored tail-out to ensure that pre-print is minimized as much as possible. This practice is also beneficial because a tape can be played and then stored without further fast spooling - most machines stack the tape far less tidily when spooling at high speed than when playing at 15ips.

                      It is sometimes found that spooling a tape through a slightly magnetized head can reduce print through (as print through is a phenomenon that resides at the top of the oxide layer) but this is obviously an extremely risky process.

                      Such is the vulnerability of analogue tape that you need to assume that every pass will be the very last opportunity to capture the content of that tape - you may well feed a roll of decent-looking tape into the head block, only to find a pile of iron-dust emerging from the other side.

                      Comment


                      • #26
                        Musicians mentally prepared

                        Originally posted by Gan CK View Post
                        I have a few direct to disc & direct cut LPs & they mostly sound more dynamic, transparent & detailed than ordinary LPs.
                        The musicians would be have to be mentally dynamic as well, as any error on their part cannot be corrected. It would mean a retake and tossing out the metal. :-)

                        Comment


                        • #27
                          Analogue anomalies Part 2 - capturing the on to and off tape signals

                          Well, I have nothing else to do today but take it easy - the perfect excuse to make Analogue Anomalies Part 2. I realised after a couple of 'takes' that I just couldn't setup the test, explain it and get to the analysis in one rigidly fixed (by the program) 5 mins. so please watch this and then holding the final scene in your mind, watch Part 3 (not recorded yet).

                          I sincerely hope that you can follow my line of attack: you can appreciate that the objective was to generate a perfect* digital multi-tone signal that represents the first five notes of an octave and then feed it into what was considered to be a very good analogue reel-to-reel tape recorder, even now. What we are interested in is the off tape signal in comparison with the perfect digital signal we delivered to the tape recorder's input sockets. For clarity I just used one channel. The record level was marked on the Revox's VU meters as 50%.

                          The tape is 'BBC Type 200' standard play. I aligned the Revox some years ago - in fact, this is the very machine that I wrote up in my HiFi News article many years ago (to follow).

                          *What is a perfect digital signal? I'd say that any signal where the random noise floor is 100dB or more below the maximum signal possible is for all intents and purposes, better than our own ears hence perfect.

                          Here is >>> Analogue Anomalies Part 2 <<<

                          Please confirm if I have presented this in an easy to follow way. The attached chart shows the relationship between the five tones I generated.

                          >

                          P.S. In experimenting with Part 3 I've devised a cunning way of showing you how much (or how little) dynamic range performance a good audio system requires. And it is a shock to me and puts the whole pursuit of sonic (digital) excellence into perspective.
                          Attached Files
                          Alan A. Shaw
                          Designer, owner
                          Harbeth Audio UK

                          Comment


                          • #28
                            An A77 user writes .....

                            Thanks for taking the time and effort to do this Alan. I too have a free day. I was listening to the Messiah and reading the new posts. I paused Mr Handel to watch Part 2 and enjoyed seeing your B77 in action. These old decks still are fascinating to watch. I have a couple of A77's but they sit gathering dust as most of the pre-recorded open reel tapes purchased during the 70's suffer "sticky shed" problems.

                            Now back to "his yoke is easy and his burden is light".

                            Comment


                            • #29
                              Analogue anomalies Part 3 - analysis of on and off tape signals

                              Part 3 displays the spectral content of the signal going into the tape recorder compared with the signal recorded onto tape and played-out by the recorder. In addition, I show that the noise floor of the Revox even using good quality tape gives it a dynamic range between the loudest signal it can record and the all pervasive tape hiss (when the recording VU needle is registering 50%) is only about 40dB in the proximity of the tones we are recording.

                              Hiss or noise is the enemy of all and every hi-fi system. Hiss or noise of any type obliterates quiet signals that are at or below the threshold of that noise. That is why a truly high fidelity system must have an adequately silent noise floor. This is an uncomfortable truth. We'll show exactly why that is in Part 4.

                              Here is >>> Analogue Anomalies Part 3 <<<
                              Alan A. Shaw
                              Designer, owner
                              Harbeth Audio UK

                              Comment


                              • #30
                                Originally posted by A.S. View Post
                                ... Hiss or noise is the enemy of all and every hi-fi system. Hiss or noise of any type obliterates quiet signals that are at or below the threshold of that noise. That is why a truly high fidelity system must have an adequately silent noise floor. This is an uncomfortable truth. We'll show exactly why that is in Part 4.
                                Hopefully you have been following my demonstrations thus far. In this final part, I have generated two tones (500Hz and 650Hz, midrange tones very typical of the spectrum of western music) but not as close in frequency as the previous five tones which represented the first five notes of an octave. I've injected those two tones into the the tape recorder. We compare the signal sent to the recorder with the off-tape signal.

                                Again, this shows conclusively that any and every microtone that has a loudness below that of the background hiss just cannot be reproduced - ever. Once a musical element is covered by hiss anywhere along the reproduction chain it is impossible to recover it. Random noise cannot ever be converted into musical tones. Once low-level transient musical tones have been swamped by hiss in the microphones, mixing desk, master tape recorder, DAC, sound card, LP, cartridge, CD transport, amplifier or even in the speaker cones themselves, they're lost forever.

                                Here is >>> Analogue Anomalies Part 4 <<<

                                Aaaaghhh! I thought I'd finished this demo but out of curiosity I thought I'd play some music for myself ..... more later!
                                Alan A. Shaw
                                Designer, owner
                                Harbeth Audio UK

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