The Lunar Orbiter tape digitization folks have just posted a commentary that bears reading by all archivists who are holding tapes. You may link to it here. The main site is www.moonviews.com

NASA, in their press conference yesterday held at The Newseum, admitted that the original 14-track 1-inch instrumentation (IRIG) tapes that contained the slow-scan video direct from the moon were most likely recycled and reused for later missions. Apparently, over 350,000 reels of instrumentation tape were recycled by NASA over time. No one apparently thought to preserve the 45-odd reels of the original moon walk.

The loss of the original IRIG tapes of the moonwalk is truly sad because this data could be re-converted to standard television formats using far superior methods than were available in 1969. There may be 2-inch helical Ampex VR-660 video tapes still extant of the slow-scan data,  but those have not surfaced. It appears that all surviving copies of the moonwalk videos are ones that had gone through optical standards converters. An optical standards converter is one that has a monitor displaying the image in real time in the transmitted standard and a television camera taking a picture of that monitor using the desired standard. Even the Australian Broadcasting Corp. tapes would have gone through this type of device, although they would be in PAL rather than the U.S.’s NTSC versions.

Lowry Digital is doing a great job of restoring what they have, but the Polaroid screen shot that survives of the slow-scan monitor is alluring of what could have been preserved. More information is available on the Parkes website and from NASA.

Vigilant migration of data as new storage techniques become available is the only way to assure long-term preservation. Even if the IRIG tapes are found, we are almost at the point where the tapes would be un-decipherable. I think one of my machines could play them (I say think as I’ve never tested it to full 500 kHz bandwidth), but I don’t have the specialized video decoder. NASA apparently preserved some equipment should the tapes ever show up.

This also raises another spectre. We MUST be selective as to what we keep in our archives because if we keep everything we won’t be able to afford it–or find it. This is one of the key jobs that archivists do. However, blindly following retention practices, as was done by NASA for the IRIG Apollo 11 tapes, needs to be tempered by historians as well. Certain small subsets of data (moonwalk slow scan video) are much more important than others (astronauts’ blood pressure and other biometrics throughout the entire flight).

All organizations who keep archives need to address this. In a generation (or less) if we save everything, it will become an overwhelming burden and the high points will be lost if they are not properly indexed.

As with much equipment–and especially with lower-cost equipment–the performance specifications and the actual operational data is not published. There are reports of the H2 clipping on the line inputs in some of the reviews and it appears that a lack of understanding how the inputs were configured exacerbated that situation.

There is nothing wrong with the line inputs on the H2. BUT there are some caveats:

1. DO NOT use the input level control on the line inputs to go below 100 or the preamps will clip before the signal reaches 0 dBFS.
   ALTERNATE WORDING (thanks Greg H.):
   Set Zoom H2 RECORD LEVEL to 100 or greater to avoid clipping at the Line In preamp stage.
2. Use an external attenuator with the gain set at 100 to avoid overdriving the line inputs.
3. The noise floor is not spectacular, but is not too bad. With the inputs terminated in 150 ohms, the peak noise was -70 dBFS, but that improved to about -85 dBFS or better, measuring it as an A-weighted rms figure, which is how most noise is measured. While this certainly isn’t what one would expect out of the Sound Devices, it is far better than the 50-60 dB(A) that one can achieve with an analog cassette tape without Dolby.
4. The maximum input level to the line input should be no more than -5 dBV or -3 dBu.
5. Try to avoid clipping as there appears to be a delayed recovery in some instances.

With this information, you can optimize a pad between the source and the H2 line input so that the recorder is never overloaded. Try to keep the levels as high as practical as there is a relatively limited dynamic range. On the other hand, I have found that the recorder noise is not objectionable even when I’ve boosted the levels 20 dB for a quiet choir piece from our church. The room ambience totally swamps the recorder noise–at least as far as I hear.

The H2’s internal mics are reasonably good for many purposes. While I still prefer the SD722 for many things, I think the H2 is one of the better oral history conversation capturing devices I’ve seen. It uses SDHC cards which may require a new card reader. Don’t use the built-in USB connection unless you’re recording MP3 files as you’ll be there all day. The internal card-reader mode is limited by the USB 1.1 interconnection. This interconnection is adequate, however, for using the H2 as a 16-bit live audio interface/microphone connected to your computer (at either 44.1 or 48 ks/s). The unit will record up to 96,000 samples per second, 24 bits,  but many of those bits will be noise.

Please let me know if this has helped or if you have any questions or comments.This work was done with version 1.50 of the H2 firmware.

The British Libary has now published his Handbook (click here).

Teaching people how to identify tapes that are suffering from sticky shed syndrome is often difficult.

I would like to propose that a careful inspection of how the tape comes off the pack may be a good way. Please provide comments as to how it’s working for you.

The tape should come off the tape pack at a precise tangent to the tape. If the tape starts to adhere and not pull off straight, that is a sure sign that the tape needs baking.

Of course, don’t bake acetate tapes even if they show this indicator, but on the last batch of questionable SSS tapes, I’ve been looking at this and it’s a fair indicator, and it seems to show at the outer edge of the pack.

More than one “test” or “factor” is needed to be sure, but this one is looking good.

Another almost sure sign of SSS is brown oxide and black back-coat.

While this is a theoretical problem, few if any good mono recorders are available for reproducing these tapes anyway, so most of us in the domain transfer field use good quality stereo machines for all cassette transfer work.

This is an interesting anomaly that should not effect operations. If you had a full-width mono head, there would be at most about a 4 dB improvement in signal-to-noise ratio vs. using one track of a stereo head (which usually results in better sound). Since the premium cassette decks, such as the Nakamichi Dragons that I use, provide very low wow and flutter, flat frequency response, a means to adjust azimuth of the play head, and gentle tape handling, all of these benefits outweigh the 4 dB or less reduction in signal-to-noise performance. If the tape hiss is a real problem (as opposed to noise recorded in from the recorder’s electronics), some of it can be effectively removed using a noise-reduction plug-in. Generally a 4 dB noise reduction in a good plug-in is transparent.

We do recommend archiving both tracks in a professional archival scenario.

The general theory behind a checksum (or “Message Digest” = “MD”) is that it provides a unique 128-bit number for each and every file, based on its content. If one bit changes, the MD5 checksum (sometimes called “hash”) changes. The checksum is repeatable, does not permit discovery of two different files that produce the same checksum, and is non-reversible (i.e. you can’t create the content from the checksum).

Common practice in audio archiving is to use 128-bit checksums, although 160-bit checksums are available. The other common practice is to take the entire filename, including extension, and add a second “MD5″ extension to that. The *.*.md5 file contains the MD5 checksum plus generally the filename.

An alternate configuration is to create one file named checksums.md5 for the entire folder to save downloading effort.

While there are many options for creating MD5 checksums, for Windows, FastSum is a convenient and low-cost package.

At any point in the future, to verify your files, you create a new MD5 checksum and compare it to the ones that were created when the file was created. If they match, you know your file has not changed. The likelihood of both the original file and the checksum file changing so that they still appear valid is essentially nil.

Some applications, like D-Space, check the integrity of all the files in the system on a regular basis using MD5 checksums.

If you receive WAV files from me, more than likely, you will also receive MD5 checksums in the same package, be that on a DVD, hard drive, or via the Internet.

It only takes a minute to create these and it truly does offer peace of mind.

I have just completed about 25 seven-inch reels of circa 1960-1965 acetate tapes (Scotch 111A, Audiotape, Soundcraft, Ampex 511, etc.) and about 20% of the tapes showed evidence of spoking after being played on the A80. These were rewound (approx 120 in/s under capstan control) on the Racal Store 4DS and then played at 15 in/s back onto their original spool.

With the heads removed, there are no fixed guides that contact the tape, just the two rolling tension guides and the capstan.

For photos of the Racal Store 4DS, please look here where I discuss its use (with head/guide assembly) for playing squealing tapes.

Please also read this post for a “do not try this at home” note.

I had the pleasure of speaking with Nadja at length about her work and I was very impressed by her approach and knowledge — as well as her practicality in getting the job done.

This document is a must-read for anyone planning a digitization project. While it is not as detailed or comprehensive as the Sound Directions publication, it cuts to the heart of what we’re trying to do in digitization. Starting with as good a playback as possible is the key to obtaining a good digital representation of the original. It also provides excellent photographs of various failure modes — and some are truly spectacular.

I must provide a disclaimer here that this website graciously links back here as well.

Oh, and the discussion started about images, but it pertains equally to audio and video. Ike was certainly clear on his thoughts about data tape. As I see it (without following it too closely), the marketplace is consolidating around LTO and appears to be shrinking, so maybe he’s right. I’ve stayed away from data tape in favour of an all-disk solution (for approximately 3 TB of storage at the moment).

When looking at storage for audio, consider a track-hour (i.e. a mono program) at 96,000 samples per second, 24 bits, is about 1 GB, uncompressed. 1 TB is about 1,000 track-hours of material at the normal high-resolution sample rate and bit depth…and that currently fits on one physical drive.

We continue to receive poorly wound tapes and are able to play them successfully. So why the quandary now? The reason is that I read portions of another Bharat Bhushan book, Mechanics and Reliability of Flexible Magnetic Media, 2nd Edition, New York, Springer, 2000. Referring to several research papers he makes a compelling case that tapes should be rewound annually if subject to storage environment fluctuations and every 3.5 years if kept in a climate controlled storage area.

If we think about the two types of stresses on each layer in the pack, this becomes more clear. There are “hoop stress” which is the circumferential stress in that individual layer and the “radial stress” which is the stress in the direction of the centre hub.

Low interlayer pressures, which predispose the tape stack to ILS [Interlayer Slip], are created as follows: the winding of successive layers of tape onto a reel increases the radial compressive stresses in the wraps of tape at and near the hub. The continued inward radial deflection of the hub converts the circumferential tensile strain in the tape, originally caused by winding, to a compressive strain….The tape, hub, and winding parameters sufficient to obtain this condition can be determined using [the complex] analysis presented in Chapter 5. A highly compressible hub, high outer-wrap winding tension, low inner-wrap winding tension, the length of tape stored on a reel, and the entrapment of air during high-speed winding are strong contributors to low interlayer pressure

The interlayer pressure from winding is further reduced by temperature and humidity cycling and/or storage….The interlayer pressure can be reduced when the wound tape is subjected to a temperature of humidity change, and is dependent on the relative value of the coefficients of thermal and hygroscopic expansion of the hub and the tape. This effect is aggravated not only by the magnitude of this differential mismatch, but also by the mismatch in the tape’s radial and circumferential coefficients of thermal and hygroscopic expansion.

Bhushan also indicates that spoking can be triggered by impact forces to the tape reel. (Dropping it?)

One of the very interesting things which is discussed is that a tapered winding tension may produce a more archival tape pack than a constant tension winding tension. This raises many questions concerning current archival practices.

I suspect that more discussion of this will occur. Please leave your comments.

If you want to record on a tape recorder (and I do not recommend doing that these days as you’re just generating more tapes that will need to be transferred later) the first thing to do is get the playback correct.

1. CLEAN the machine.
2. If you haven’t done it in the last year or after a move (depending on the machine), demagnetize the heads and guides (using a strong demagnetizer like the Han-D-Mag).
3. Get a NEW (or trusted) calibration tape from MRL
4. The MRL tapes are supplied tails out. Rewind carefully and slowly onto a large-hub reel.
5. The first tone is a lineup tone, set for 0 on the VU meters of all channels.
6. If you are compulsive, the first time you do this, check the VU meter calibrations using an external AC voltmeter with wide frequency response. Most professional decks have very flat VU meters, so once you confirm that, you can just use the VU meters for the alignment.
7. There is a second lineup tone at different levels. If it is one of the -10 dB levels, take the machine out of playback cal and increase the level so that the meter again reads 0 VU.
8. On the 8 kHz azimuth section align the playback head azimuth (with an oscilloscope or a scope-application in the DAW) for minimum phase shift. Also check in mono sum.
9. Adjust the EQ trims (Trans-treble on the Studer A810/flashing treble light) for 0 VU.
10. On the 16 kHz tone, readjust the azimuth for minimum phase difference and maximum amplitude as above. Check in mono sum as well. It will never be perfectly stable.
11. Low frequency adjustment cannot be accurately accomplished off a test tape due to fringing unless the test tape and the play head track width is matched. However, one can often get close a test tape, but don’t necessarily tune for flat. It’s best to leave this alone if you can. The right channel of quarter-track machines will show more bass than the left as the fringing effect is coming in from both sides. Read the material on the MRL website.
12. Finally, recalibrate the playback level setting on the last tone. Leave the tape in a played wind on the reel it came on.

This completes the playback adjustment. Now you are ready for record adjustment.

1. Place a piece of blank tape on the machine (NOT your calibration tape from MRL)!
2. Record a 700 Hz tone at 0 VU on the meter when monitorin input and adjust the record level calibration for 0 VU when monitoring the output. Do this for all tracks.
3. Increase the frequency to 10 kHz (and drop it 10 dB at slower speeds, making up the gain in the uncal portion of the playback gain controls).
4. Decrease the bias level slightly so that you can find the peak. Then increase the bias past the peak until the 10 kHz level off the tape drops by the amount specified for that particular tape. It’s often somewhere around 3 dB. There are other, more precise ways to do this, but this should get you close.
5. Do a sweep of the high frequencies and adjust the HF record equalization for response closest to the response you got from the test tape. DO NOT try and improve the response from the test tape while adjusting record EQ as that will give you non-standard tapes.
6. Do a sweep of the low frequencies and then you can better adjust the PLAYBACK LF equalization.
7. Go back to 700 Hz and adjust for 0 on the VU meters when reading input.
8. Adjust record level control for 0 on the VU meters when reading output.

That should do it. I generally do a quick check flipping between input and output monitoring and you should hear no difference.

A word about levels. In the old days, I used to record at 185 nWb/m with Dolby A. With more modern tapes, 250 nWb/m will provide adequate headroom in most cases and may reduce the need for noise reduction processing. However, some have complained that 250 nWb/m is too low as it sounds too “digital” (i.e. “clean”). If you want to use tape as an effect, increase the record level to taste.

I really love recording with my Sound Devices 722 or somewhat less so with my MOTU 828 MKII, though there is nothing wrong with the MOTU that an RME FireFace 800 wouldn’t fix! Of course, now MOTU has the new 828 MKIII and it seems they have improved some of the things I complained about, but … twice burned (8Pre, also) … Anyway, I think that quality digital recording will capture sounds closer to the original than analog magnetic tape. This has been true in most tests run since the early days of digital recording and why most of the classical engineers who are looking for accuracy and not colouration were early adopters of digital. If you wish to record on analog that’s wonderful, but consider that analog tape is being used as much as an effect or sound-colourant as it is a storage medium. Also, remember that your legacy of tapes will be much more costly to preserve and migrate than digital files, although they may withstand neglect better.

Doug Pomeroy commented:

After aligning the deck for playback, per Richard’s list, there is a simple way to set bias on any machine, recording on any tape. Use a 1000 Hz test signal and set bias current for maximum recording sensitivity (VU meter reading). Then for 15 and 30 ips recording, increase the bias until the
output level drops 0.2 dB. For 3.75 and 7.5 ips recording, decrease the bias until sensitivity drops 0.1 to 0.2 dB. One slight problem with this is being able, accurately, to read such small values on a conventional VU meter! (This method comes from Jay McKnight, of MRL Labs.)

Another method, also requiring a tone generator, is to record a low frequency, such as 30 Hz, at a very low level – at least 20 dB below normal operating level – and crank up the playback level enough to hear the output clearly, then adjust bias for the minimum amount of distortion (modulation noise, actually). This method allows one to easily adjust the bias by ear, listening for the cleanest reproduction of the low tone. The point of minimum modulation noise will very closely match bias settings arrived at by more elaborate means.

OF COURSE, after setting bias one must always go back and look at the high frequency response (10 kHz) and readjust the recording eq for flattest response.

Yes, bias setting is somewhat complicated, but it is good to remember it is always a matter of compromise, between the least distortion on the one hand, and the flattest overall high frequency response on the other.

Thanks for the comment, Doug. These are also good ways to set the bias. It is always a tradeoff. I no longer remember all the details, but biasing some old Magnetophonband Typ L from circa 1943 was a real challenge on a modern recorder as it is a homogeneous tape which means the “magnetic coating” is much thicker than on any coated tape, so the thickness loss is greater, and its basic sensitivity was far less than even something like 3M/Scotch 111.

]]> http://richardhess.com/notes/2008/02/02/aligning-a-tape-recorder/feed/ 0 http://richardhess.com/notes/2008/01/09/using-the-proper-toolsand-dont-try-this-at-home/ http://richardhess.com/notes/2008/01/09/using-the-proper-toolsand-dont-try-this-at-home/#comments Thu, 10 Jan 2008 03:10:08 +0000 Richard L. Hess http://richardhess.com/notes/2008/01/09/using-the-proper-toolsand-dont-try-this-at-home/ I didn’t think I needed to write this post, but it appears that someone purchased a Racal Store 4DS Instrumentation Recorder at least partially because I mentioned it, hoping that it would work as a four-track recorder for creating music.

Well, this is not a good idea. The machine uses non-standard-to-audio equalization. There is no “sel sync” (Ampex TM) to play back previously recorded tracks in time with newly recorded ones. There is no individual-channel erase system (and no erase head at all on the 7DS 1/2-inch, 7-track machine).

While this machine is useful to me for professional tape restoration. With a knowledge of its shortcomings and benefits, it can be a useful tool. I’m afraid, however, that I need to say, “DON’T TRY THIS AT HOME”!

In general, there are things that are posted on this Blog that if used inexpertly can fail to meet expectations and perhaps do damage. In this case, it only caused disappointment.

Specifically, instrumentation tape recorders were designed to gather data in the field and then permit later analysis of that data in the days before digital computers could do this much better. Audio and instrumentation look a lot alike, but are different enough that unless you completely understand the intiricate details, you will be disappointed.

I would also suggest that using the one-piece hard-disk-based digital music-production units from a variety of manufacturers will go much farther to enhancing your creative musical expression than an instrumentation recorder or even a cassette “porta studio”. I am not in a position to recommend any particular unit.

]]> http://richardhess.com/notes/2008/01/09/using-the-proper-toolsand-dont-try-this-at-home/feed/ 0 http://richardhess.com/notes/2007/11/21/how-to-play-4-track-1875-ins-tapes/ http://richardhess.com/notes/2007/11/21/how-to-play-4-track-1875-ins-tapes/#comments Wed, 21 Nov 2007 16:25:53 +0000 Richard L. Hess http://richardhess.com/notes/2007/11/21/how-to-play-4-track-1875-ins-tapes/ I received a query from a gentleman in Europe about 1.875 in/s 4-track tapes. He was frustrated in finding a good machine for transferring them. Apparently, they have many of these tapes. Here are my suggestions.

Perhaps the easiest answer is to find a Studer-Revox C274 with low speed options. They were made.

Two other options. 

(1) the Sony APR-5000 will go to 1.88 in/s by using its -50% varispeed. Most of the ones I’ve had do an adequate job at that speed, but I’ve been cautioned by the ex-Sony guys on my Sony APR mailing list that this is way outside of design spec. I use Nortronics in-line 4-track heads, but I’m also in the middle of building a staggered 1/3, 2/4 head assembly since that will improve inter-program crosstalk. None of these heads do really well due to gap length considerations. I suspect (I haven’t done the math) that you want a 50 micro-inch or shorter gap to do this well.

(2) The Racal Store 4DS instrumentation recorder which has constant-flux playback equalization (needs to be filtered in the computer afterward) and is not fantastic for S/N ratio actually goes to 15/16 in/s and is a 4-track machine. The previous two entries here feature this interesting machine. I did invest in three of them (the one in the pictures is the prettiest) as well as a 1/2-inch 7-track 7DS.

Someday, I might get a C274 logger…but I prefer adapting versatile transports to specific applications rather than collecting dedicated-per-format machines.

]]> http://richardhess.com/notes/2007/11/21/how-to-play-4-track-1875-ins-tapes/feed/ 0 http://richardhess.com/notes/2007/09/20/can-i-destroy-my-originals-after-i-digitize-them/ http://richardhess.com/notes/2007/09/20/can-i-destroy-my-originals-after-i-digitize-them/#comments Thu, 20 Sep 2007 20:36:45 +0000 Richard L. Hess http://richardhess.com/notes/2007/09/20/can-i-destroy-my-originals-after-i-digitize-them/ Jill Hurst-Wahl in her excellent blog “Digitization 101” asks this question and provides some good answers with reasons. You can read it here.

]]> http://richardhess.com/notes/2007/09/20/can-i-destroy-my-originals-after-i-digitize-them/feed/ 0 http://richardhess.com/notes/2007/09/12/playback-of-nab-2-track-tapes-on-a-din-stereo-butterfly-head/ http://richardhess.com/notes/2007/09/12/playback-of-nab-2-track-tapes-on-a-din-stereo-butterfly-head/#comments Wed, 12 Sep 2007 15:12:56 +0000 Richard L. Hess http://richardhess.com/notes/2007/09/12/playback-of-nab-2-track-tapes-on-a-din-stereo-butterfly-head/ I received a query from Sweden today asking

I have a Studer machine with butterfly heads with which I’d like to reproduce
tapes recorded with normal two track heads. Theoretically, how much more noise,
in dB, would I get from playing the “empty” part of the tape? 

Let’s look at the assumptions.

Studer talks about 2 mm and 0.75 mm guard bands.

If we take the width of the tape at 6 mm (6.35 mm to be exact, but we have to leave a little guard band at the edges) that gives us NAB tracks of 2 mm and DIN tracks of 2.6 mm

As a quick crosscheck, 2 mm is 79 mils which is between the Ampex standard of 75 mils and the the NAB standard of 82 mils. Close enough.

Let’s first review the calculation for the case of NAB vs DIN with matched heads.

Signal goes up 20 log (2.6/2.0) or 2.28 dB because it’s all in phase
Noise goes up 10 log (2.6/2.0) or 1.14 dB because it is random
for a net S/N improvement of 1.14 dB

For the NAB tape played back on the DIN heads,

Signal doesn’t go up
Noise goes up 1.14 dB
Net S/N degradation of 1.14 dB

One other major consideration: IF there is JUNK in the NAB guard band, then all bets are off. This includes centre track time code (CTTC) as well as gapped erase heads on the recorder (common on most consumer recorders from the ReVox A77 on down). Pro machines that used Woelke erase heads only had gapped erase heads when there was CTTC (at least in the Studer A810 and Sony APR-5000 series). The plain stereo machines that I’ve seen have had the “checkerboard” erase heads that fully erase the entire width of the tape and if they miss anything it’s right down the centre and still won’t impact the DIN playback heads.

I am a purist about this and regularly swap DIN/NAB heads on my A80s when I have DIN recordings — I can also do it on my APR-5000s and my A810s but most DIN recordings get the A80s as they sound a hair better than the APRs which sound a hair better than the A810s, but all are really quite close.

With all the math, the reality is that many archives are using DIN playback machines here in North America as the largest group of surplus, well-cared-for machines to hit the market came from CBC which used DIN heads in many applications.

I would rather play an NAB tape on a Studer A807 with butterfly (DIN) heads than on a ReVox A77 with NAB heads if there is no centre channel junk. And since I think the A807 isn’t as good a playback deck as the A810, the same holds true more so with the three above-mentioned machines. But, I’d rather play an NAB tape on a Sony APR with wideface Applied Magnetics heads than on a Studer A80 with butterfly (DIN) heads.

Content and care of original recording also matter. If these are special recordings and there are enough of them, I’d go to the trouble of putting an NAB head in a spare headstack for your machine.

]]> http://richardhess.com/notes/2007/09/12/playback-of-nab-2-track-tapes-on-a-din-stereo-butterfly-head/feed/ 0 http://richardhess.com/notes/2007/06/20/seeing-the-tracks-ii-an-improved-magnetic-viewing-system/ http://richardhess.com/notes/2007/06/20/seeing-the-tracks-ii-an-improved-magnetic-viewing-system/#comments Thu, 21 Jun 2007 02:41:31 +0000 Richard L. Hess http://richardhess.com/notes/2007/06/20/seeing-the-tracks-ii-an-improved-magnetic-viewing-system/ I first wrote about seeing the tracks here in March of 2006. While these solutions work, the Plastiform viewer needs to be kept in a humidor and the Kyread spray is a bit of mess to use and the results are variable. One result of the Kyread treatment can be seen here (please wait for the pictures to load, it’s a big page).

Here is what appears to be a vastly improved solution:

The image above shows the view of a 4-track 1/4-inch tape and the reticle from the B&L magnifier. Track 4 (at the top) shows slightly at the top right and then fades out. Images made with Nikon D200 and Nikon 105 mm f/2.8 Micro-Nikkor without the magnifier lens attached. The following image shows an overview of the magnifier and viewer on an A80RC.

 

When some of the folks on the Studer list started discussing the Sigma Hi-Chemical MV-95 magnetic viewer (seen here), I was curious. It is not inexpensive, but a kind list member set up a group buy and I bought one and am very impressed. It is slower to react, but after a minute or so, it gives a very good image of the track format and shows signals at a lower level more easily than either of the previous two products.

To round out the “kit” I decided I needed another magnifier and the good folks at Efston Science in Toronto recommended a Bausch & Lomb 7X Hastings Triplet Measuring Magnifier with the 81-34-36 General purpose scale. This is a compact unit with scales of 0.5 inch, 10 mm and a quadrant of angles, among others. Calibration is 0.005 inches and 0.1 mm and one degree. Here is the B&L page for this product. It appears that many online retailers sell this. Peak makes a similar unit (here or here) called the Mini-Comparator 7X. An alternate reticle might be more useful than the simple metric one that normally comes with this. I like the one that came with the B&L which is almost identical to the Peak #12 (shown here). I would consider both inch and metric scales as I think about track widths in both measurement systems.

Of course, you’ll need more light, and the ever-handy Surefire LED flashlight is my tool of choice. Here is my page about flashlights.

I often place things like this behind the head stack on a machine. Be careful on an A80 as there is a round-head screw that could damage the thin bottom metal sheet of the viewer. I removed the screw.

]]> http://richardhess.com/notes/2007/06/20/seeing-the-tracks-ii-an-improved-magnetic-viewing-system/feed/ 0 http://richardhess.com/notes/2006/09/27/azimuth-hows-and-whys/ http://richardhess.com/notes/2006/09/27/azimuth-hows-and-whys/#comments Wed, 27 Sep 2006 16:07:38 +0000 Richard L. Hess http://richardhess.com/notes/2006/09/27/azimuth-hows-and-whys/ There is a recurring question as to what is the best way to set azimuth for playing a tape. Many people assume that using the test-tape alignment is best. Well, that makes another big assumption: The recorder used a proper test tape alignment. While that can be the case, it usually is not.

If the tape has tones on it (a big if in many collections), you align to that, right? Better, but consider this: When a 1963 album was being remastered, the mastering engineer aligned to the tones and after doing all his magic found that the tones were not recorded at the same azimuth as the program. Big redo!

Aligning to the track material itself is the only way to properly adjust azimuth in the absence of tones and it is still necessary to check the track material even if there are tones. The wider the track and the slower the speed, the more critical the azimuth adjustment is. Stereo makes it more critical and often times easier to adjust.

What is azimuth? It is simply the angle of the recording or reproducing head gap relative to the motion of tape travel. It should be perpendicular. 90 degrees. 90.000 degrees. But there are limits to the accuracy of even the best test tapes. And there are limits to the operator’s ability to adjust the machine. And the machine is subject to vibration and shock in its life. Here is an excellent paper by Jay McKnight of Magnetic Reference Lab about how they do azimuth and the limitations. Figure 6 of this MRL paper shows the frequency response when the azimuth is varied from optimum. What happens is that there is a combing effect and that can not fully be removed by re-equalizing after the transfer. Therefore, despite hardware and software “azimuth correctors” that are available, it is best to align the playback azimuth as best you can prior to transferring the tape — and do it with program.

Properly adjusting azimuth to program takes practice. If you have a mono tape, that’s all you have, but if you have a stereo or multi-track tape, you can sum channels that have similar program on them that should be in phase and get a wider baseline for tweaking the azimuth. Of course, gap scatter in a multi-track head, especially, can corrupt this approach. Gap scatter is the linear distance along the direction of tape motion between gaps in a multi-track head. It should be 0 which means all tracks’ gaps are in perfect vertical alignment. With stereo or multi-track recordings, you can use a phase scope to narrow the line of the mono component. Dale Manquen commented that he thought gap scatter was more of a problem than I made it out to be. He offered the following suggestion:

If you use a dual-trace chopped display triggered off one track, you can simultaneously see azimuth peaking in the amplitude, and time errors in the time offset. If the amplitude and phase adjustments don’t coincide, then you would have a starting point for the time offset due to gap scatter.

Adjusting azimuth is very similar to manually focusing a camera lens. You rock through the point of best azimuth and see how far out it is on either side and try to manually find the centre between two equally bad side points. You tune for MAXIMUM high end. Don’t worry about making a tape screachy or annoying — all you’re doing is capturing what’s on the tape. There is no point of azimuth adjustment that will make the tape brighter than the original recording. Anything but the proper azimuth will produce a tape that is duller than the original recording. The point of proper azimuth is very narrow. Often, the best performance will be within +/- 5 degrees adjustment of the azimuth setting screw. Make sure you’re listening to the highs as you do this. If the cymbals stop, go back to where the cymbals are. If you don’t have cymbals, listen for whatever high end you have. If you don’t have good speakers, use headphones. Remember to listen to stereo programs in mono.

One word of caution, especially with tones: You can set the azimuth to a false peak. This happens most often on narrow tracks. Checking with the voice announcements on a test tape will tell you if you’re close. It’s possible to have 8 kHz in phase on a stereo machine, appearing to be proper azimuth, and still have 4 kHz out of phase. If that happens, go back and tweak the 4 kHz and then proceed up the scale. This error is actually less likely on program material than on tones. The one time this happened to me was the first time I aligned an 8-track 1/4″ head. I wasn’t used to very small difference between the main peak and the peaks on either side of the main peak due to the very narrow (21 mil) track width.

Here is an example of a 1.88 in/s mono two-track tape that was recorded with, I believe, test-tape setup followed by the same section after I adjusted azimuth to the program. In the piano section of the demo, you can actually hear the “combing” effect in the first section. There is some digi-junk even though it’s a 128 kb/s MP3, but you should be able to hear through that.

It is critical to play the tape with the proper azimuth. Remember, at this point in the tape’s life, this might be the last playing as you digitize it. Make sure it’s the best playing you can give it.

Bertrand Navarro commented:

Hello,

I’ve leave a comment here because i’ve been working for the past two years on a new system that basically remove the burden of azimtuh adjustment.

I work in a R&D data storage company and we developped a system based on our previous magneto optical data reader.

We demonstrated that with magneto optical reading of the tape we can reach pretty good performances (SNR, Bandwidth, and THD). Plus, instead of using a single head, we’re generating a laser line across the tape which is then imaged onto a photodiode linear array. The main idea is to reduced the indivual height of each optical head and then lower the constraint on the azimuth alignment. The azimtuh is seen as phase shift between optical signals and can be corrected by simple signal processing. So bassically you just have to set the head close to 0° azimuth but this setup can be done with less constraint. Furthermore, is the azimuth changes during playback (Tape written on two different decks or LTM), it can also be corrected by post processing.

I hope this technologies will be push forward to help in the preservation process that is going on.

If you want more information you can contact me at bnavarro@hi-stor.com

Regards

Bertrand NAVARRO

Posted Apr 3, 2007 7:53 AM

]]> http://richardhess.com/notes/2006/09/27/azimuth-hows-and-whys/feed/ 0 http://richardhess.com/notes/2006/08/17/dss-and-other-compressed-digital-files-in-an-oral-history-archive/ http://richardhess.com/notes/2006/08/17/dss-and-other-compressed-digital-files-in-an-oral-history-archive/#comments Thu, 17 Aug 2006 16:09:03 +0000 Richard L. Hess http://richardhess.com/notes/2006/08/17/dss-and-other-compressed-digital-files-in-an-oral-history-archive/ With budget limitations, it appears that oral histories are being recorded with little thought to their long-term preservation. While this appears to have been the case in the past as well, with purchasing agents buying the cheapest white-box tape that they could find, continuing this into the digital age needs to be reconsidered.

The cost savings in using bargain-basement digital speech recorders are offset by the labour required to reformat these files upon their receipt by an archive and also the fidelity of the recording suffers, and with fidelity, intelligibility also suffers.

DSS was an industry standard agreed upon by Olympus, Grundig, and Philips in 1994. Like the compact cassette and the micro cassette, this format was developed for dictation. My perspective is that oral history is more than dictation, although the DSS format claims no loss when compressing a WAV file. It includes nuances and other cues that are often lost in the dictation-only environment. My personal preference is for stereo recording of oral histories, but that is certainly not universally accepted.

While Olympus claims that DSS offers future-proof access to recordings, it becomes another standard that must be maintained and should converters become unavailable for new platforms, then the entire archive will need to be reformatted at that point.

The oral history resources I have listed here are generally looking at archiving WAV files. CD-quality WAV files should be more than adequate for oral histories, but that is a far different quality level from DSS.

There are a variety of software packages that will convert from DSS to WAV files. Switch (a great free utility) will convert SP mode, unprotected DSS files and a host of other file formats to WAV (and MP3). Olympus has a player as well.

The decision to archive in WAV or MP3 is tough. While concatenation of compression (stringing two compression cycles together, end-to-end) is considered poor form, if the MP3 file is not too heavily compressed, then there is saving vs. archiving in WAV if the program material originated in another compressed format. Tests with program material and critical listening should be undertaken prior to accepting this. If the decoded DSS or other compressed file is stored as a WAV file, then nothing is lost. The amount lost with (for example) a well-compressed 96 kb/s mono MP3 file at 44.1 ks/s will be low.

Archiving WMA files is another question. As long as Windows Media Player is available, these files should be playable. I’m not sure about the cross-platform compatibility of these files, so that is a negative at the start.

The best suggestion is to archive as few different formats going forward as possible, and then make sure at each major upgrade of software that these files will all be accessible.

A comment:

Your readers may also be interested in the Acappella Conference Audio Recorder and Playback Assistant which improves the reliability of transcripts and the time taken to produce them by recording in CD quality audio and telling the typist during transcription the name of the person speaking.

http://www.acappella.com.au

http://audiorecorder.wordpress.com

[Blogowner’s comments: This was posted by someone who appears affiliated with the company. We have no experience positive or negative with this system. It appears capable and I released the comment to the blog but am adding this note that this is not an endorsement, but you should review it as a possibility and see if it meets your needs.]

]]> http://richardhess.com/notes/2006/08/17/dss-and-other-compressed-digital-files-in-an-oral-history-archive/feed/ 0 http://richardhess.com/notes/2006/07/24/noise-reduction-plug-ins/ http://richardhess.com/notes/2006/07/24/noise-reduction-plug-ins/#comments Mon, 24 Jul 2006 12:37:52 +0000 Richard L. Hess http://richardhess.com/notes/2006/07/24/noise-reduction-plug-ins/ The question seems to regularly arise on mailing lists and chat rooms about Dolby and dbx plug-ins. I don’t think it will happen and I added that comment and some hopefully helpful operational hints to my noise-reduction page, here.

]]> http://richardhess.com/notes/2006/07/24/noise-reduction-plug-ins/feed/ 0 http://richardhess.com/notes/2006/05/17/sticky-shed-loss-of-lubricant/ http://richardhess.com/notes/2006/05/17/sticky-shed-loss-of-lubricant/#comments Wed, 17 May 2006 23:51:20 +0000 Richard L. Hess http://richardhess.com/notes/2006/05/17/sticky-shed-loss-of-lubricant/ This post has been updated as: http://richardhess.com/notes/2007/03/21/soft-binder-syndrome-and-sticky-shed-syndrome/

For a current list of degrading analog tapes, click here.

For several years, we have been discussing the differences between Sticky Shed Syndrome (SSS) and Loss of Lubricant (LoL).

Recent work in which I’m participating seems to indicate that what we thought was happening in both instances may not be really what is happening.

For now, the continued recommendation is to bake tapes for which baking works. These include:
Agfa (pre-1990): PEM 468, PEM 469
Ampex/Quantegy (1970s-1980s): 406, 407, 456, 457
Note: Recent reports indicate that these problems may exist in tapes made in the 1990s
and later, even under the Quantegy name.
Audiotape/Capitol (early 1980s): Q15
Note: This tape may or may not respond to baking. Some tests will be conducted soon.
Scotch/3M: 226, 227, 806, 807, 808, 809

If these are squealing and leaving deposits, they should be baked (at your own risk). The Ampex patent for baking tapes can be found here.

The classic test for determining if a tape is suffering from LoL has been to bake it and see that baking fails. The assumption has then been that it is loss of lubricant. This test, however, may exacerbate the condition and it is not recommended to bake suspected LoL tapes.

Tapes which appear to be suffering from LoL include:
Scotch/3M: 175 and Melody 169 (a seconds brand of Scotch)
Sony: PR-150
Pyral: (type numbers unknown for this French tape)

We have seen cassette tapes also suffering from LoL.

There are several ways to address playing LoL tapes, but, for the moment, we are not prepared to publish anything definitive beyond Marie O’Connell’s tried and true method shown here.

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