TECH TALK β€” 30 April 2015

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The following post was written by Fred Thal and is presented as a guest editorial…enjoy.

Are we squandering the last opportunity to preserve our recorded music heritage in the highest fidelity?

The new transfers being done today could be the very last time that most surviving analog master tapes are ever played back. It’s because all archived audio tapes are undergoing chemical changes with time, and many are becoming increasingly problematic and fragile.

Analog audio tapes can be broadly classified into two main types, according to the composition of their base films: cellulose acetate and Mylar. Each type has its own characteristics and long-term aging profile. Acetate tapes are vulnerable to becoming brittle and weak. Mylar tapes appear to have a more stable base film, but can exhibit chemical instability in the binder, the compound that solidifies and glues the magnetic oxide layer to the base film. Softening of the binder (termed soft binder syndrome) is commonly seen on Mylar tapes and this can develop into sticky shed syndrome. As the name suggests, sticky-shed tapes can shed oxide, leave deposits and stick to a tape machine’s heads and guides, often slowing down and sometimes even stopping the machine.

The mechanism responsible for moving the tape at a perfectly constant velocity over the sound heads of an audio tape machine is known as the tape transport. Transports can be classified according to their design and their construction. They can be simple (constant torque) or complex (constant tension). They can be servo controlled, or not servo controlled. The mechanics of tape guidance in the transport defines the path that the tape will follow. In the case of transports designed for the common, quarter and half-inch tape widths (almost all surviving mono and stereo master tapes are in these two tape widths) there are both force-guided and precision-guided transport designs.

Force-guided designs are inexpensive to build and thus they account for more than 99 percent of all tape machines ever manufactured. Force guidance overcomes problematic zenith-error tape steering by literally forcing the tape to follow from point to point thru the tape path by the imposition of tape edge guides. But the tape edge is where the vulnerable oxide layer to base film junction is exposed, and forced guidance harmfully abrades this boundary, often causing roughening and wrinkling of the tape edge which can lead to problems including shedding and spacing loss.

Cost-no-object quarter and half-inch transport designs employ precision guidance, an architecture that does not force the tape to travel within a plane, but rather allows it to. With a precision guided transport, precision guided headblocks can be fitted to achieve very low levels of scrape flutter. This can make an audible improvement.

Another completely avoidable tape damaging feature found on most tape machines are fixed-pin tape lifters, used in inexpensive transport designs to lift the tape away from wear-prone tape heads during fast winding. For a tape with soft binder syndrome, just one pass over fixed lifter pins can cause irreparable harm to the oxide layer. Viewing tape under a stereo microscope confirms this.

We have been aware of tape chemistry degradation problems for thirty years and the fragility of surviving master tapes should make it unacceptable to employ traditional studio tape machines for their playback. But we have not yet seen the music industry respond responsibly. Instead, popular work-arounds, such as baking sticky shed tapes, are exclusively relied upon, while the work continues using the same old hardware.

It might appear that a solution for working with high-value master tapes is to obtain old tape machines employing precision guidance and not having fixed-pin lifters. Examples of quarter and half-inch machines fitting this description are the Swiss-manufactured Studer A820 and its predecessor, the A80. Another is the German-manufactured AEG M20.

But these machines will not perform properly today, as they are now far beyond their expected operating life before complete overhaul. A major issue is precision bearing lubricant dry-out, which destroys the transport’s guidance and the machine’s once exemplary low flutter performance. Importantly, correct bearing replacement in these machines can be much more involved than what might at first appear. It is not a simple matter of just exchanging the bearings for new. Unfortunately, most tape machine service expertise here in the USA is of little help with the precision Studers and AEGs, as our industry grew up almost entirely around maintaining Ampex recorders. If you don’t know how a precision guidance tape transport is supposed to work, you’re probably not qualified to be taking it apart for re-building. It’s akin to taking a Ferrari to a Ford garage.

About the author: Adolph Friederich Thal is managing director at ATAE, a California firm that manufactures professional analog audio tape playback hardware.

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(11) Readers Comments

  1. All the technical assertions are correct. No matter how carefully stored and preserved, the more signal level and bandwidth there is on the master, the more the analog tape will be subject to a higher degree of deterioration over time.

    But… that’s why we have archivists and technology to preserve and pass on the master tape grade information. A well preserved, high quality, analog master tape carefully transferred at 24/96 still has plenty to show that was not revealed on LP or CD, and thus can provide a level of listening quality not previously experienced.
    In fact, the Almeida/Byrd disc you so nicely re-mastered for DVD-A is a great example of this; forget the semantic mess that the term hi-res has brought.

    Incidentally, the one publication that actually is 110% qualified to review the Pono player, Stereophile, gave it a rave , didn’t hide the hangups with the music service, but as do I,they know that there is a reason past money that Neil Young has campaigned and complained about the shitty sound of MP-3 downloads. Whatever valid criticisms and objections are raised, it strikes me as , well, I’ll just use the word nonsensical, when there is a non-material reason that was the original motivation; enjoy music more with clean sound. Musicians are not always wise businessmen, but it’s their hearts and spirit that make them stand out. This attitude of “First…suspect sin” does not and will never represent progress.

    You can promote your own work without dumping on someone else’s

    • You really don’t want to let go of the Pono thing do you Craig. Reporting on the missteps that Neil and his group have made needs to be done. Hiding the warts only makes things worse. I’ve never said that the Pono player is anything but a very fine portable device. It’s not capable of delivering real high-resolution audio, but neither are the other portable machines. The insistence on calling CDs “high-resolution” is BS and they should stop. When over 99% of the tracks you can download are standard definition tracks ripped straight from 44.1 kHz/16-bit tracks there is no “better” there.

      • Mark, I completely agree and support your position on Pono, HDTracks, etc on advertising their up-sampled downloads as being HDA sound, but,

        “It’s not capable of delivering real high-resolution audio, but neither are the other portable machines”

        That statement confuses me? If I were to load one of your HR files into a Pono player or A&K, and it’s output into a set of headphones capable of HR specs, or even into your own HR studio playback system, what aspect of their performance would restrict them from a HR delivery?

    • Amen!

  2. Mark,

    So if I play your High Resolution files on the Pono player are you saying it is not capable of delivering high resolution audio?

    • The actual fidelity of the analog output will not be as high as with a home system…the actual specs won’t make true high-res. Even most home machines fail to deliver better than CD quality.

  3. Accepting a file with real highres specs is not the same as ‘outputting’ it so.
    Most ‘machines’ do up/downconverting/reconverting before the bits are delievered to the output stage of the DACs.
    There often are some weird things going on in the DAC-solutions of today – not very transparent.

  4. Out of interest does ATAE have a solution for transferring original 16 track analogue master tapes? Their site seems to indicate they only do 1/4″ and 1/2″ decks which must means no matter how well they perform, you are dealing with at least 2nd generation copies?

    I recently purchased the DVD-A of ELP Trilogy album. Originally recorded on 16 track analogue equipment, the producer Jakko Jakszyk notes he was given, not analogue tapes but a disk of digital files (format not specified) transferred presumably from the original 16 track masters. Without knowing on what decks they were transferred nor the resolution of the transfers, it’s hard to know if the “best” possible source was used for the new release.

    • My guess would be that ATAE doesn’t work in the multichannel area. The 1/4″ and 1/2″ analog tape masters that exist are already mixed and approved by the producer and artists. Those are the ones that a company like ATAE wants to make sure get transferred at the absolute best quality…and which is not being done now.

  5. > does ATAE have a solution for transferring original 16 track analogue master tapes?

    Yes, we can supply two-inch reproducers for such work.

    However, re-issue producers and mastering engineers know that a huge issue with going all the way back to the multi-track master is that you are very likely to lose the original artist approved mix.

    To demonstrate, let two people each sit down at a mixing console, with the same sixteen (or twenty-four) track master. Let them work independently on mixing this down to stereo and you will get two entirely different sounding mixes. Listeners might not even recognize that they came from the same master tape.

    So, although it is down a generation, retrieving the artist’s own produced stereo mix master tape is most often what brings us closest to hearing the original work.

    Fred Thal
    ATAE

  6. My “Amen” is to Craig Allison’s post.

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