The tapes were originally recorded in about 1978-1979 and he said that he needed them to have Dolby C noise-reduction processing applied to the files.

I did a bit of research, as that did not sound correct from an historic point of view.

Here is an approximate chronology of the major noise-reduction systems and their dates of introduction:

DOLBY
A – 1967 (pro)
B – 1971 (consumer)
C – 1983 (consumer/prosumer)
SR-1986 (pro)
S – 1990 (consumer/prosumer)

dbx
I (pro) & II (consumer) – 1971

Telefunken (later ANT)
C4 – 1977

He later wrote me back saying the engineer was pretty sure it was Dolby A.

When I applied Dolby A, Dolby B, Dolby C, dbx I, and Telcom C4, only the dbx I sounded close to correct.

Fortunately, dbx I is less critical than the Dolby noise reduction systems for accurate level setting, since there are no test tones digitized along with the audio.

This work requires playing the digital files out through the D-A converter and then re-recording them via the A-D converter.

I recently unearthed 26 brand new 10 1/2-inch reels of 456 from 8 different batches. I checked one reel from each batch by playing them back and forth at 15ips (I only played the bad reels in one direction – that was enough!). The following batches were bad:

90297, 91049, 91055, 91079 and 91149

The following were fine:

94132, 94133, 94298 and 96190

The reels that were bad did not squeal during playback, but left debris on the heads and guides that was just barely sticky, so these are obviously in the beginning stages of deterioration.

All of these were Ampex (pre-Quantegy) tapes purchased in the early 1990s. Batch 96190 have lighter grey boxes as opposed to the textured, darker grey background found on the earlier batches, and the reel labels appear to be silk screened, rather than having sticker labels. None of these reels have the old rainbow-style logo.

I would guess that the good batches will probably remain OK – they’ve had a good 17 years to go bad and would probably have done so by now if there was a problem.

For whatever it’s worth…

Gary Galo
Audio Engineer
SUNY Potsdam
…speaking for himself

For AAs and AAAs, I have selected the Maha Powerex Imedion cells which retain a charge for an extended period of time (spec’d at 15% loss per year). I have invested in two of the MH-C9000 Wizard One chargers for my office and two MH-C401FS Mini chargers, one for my bedroom and one for the church sound booth. These are both available alone and in kits with cells from Paul’s Finest where he is selling the international version with a multi-voltage “wall wart” for a reasonably good price with great service.

While the MH-C401FS charges batteries individually, and does a good job of it, the MH-C9000 Wizard One is amazing. It will determine the remaining capacity and will even test and condition cells to the IEC standard. For example, I was having a problem with some cordless phones that used 3-cell NiMH battery packs. I took the pack apart and put the three cells in the MH-C9000 and it told me that they had a capacity of about 70, 40, and 40 mAh for each of the three cells. I immediately replaced these three cells with three new Imedion AAA cells that have about 800 mAh capacity each.

I have been using the Maha cells and chargers since April and am very pleased.

A special-purpose option in this are the 3.7 V 14500 lithium polymer AA-sized cells. These will obviously damage many devices that could physically accept them, but for the latest breed of LED flashlight, such as the 4Sevens Quark AA lights (USA site),  these provide superior peak output at the highest setting with the understanding that you can also use standard NiMH cells in an extended emergency with the loss of some peak output.

I have been using the AW-139 dual-cell fast charger also since April with great success. These will charge the 14500 cells mentioned above as well as 17670 cells which are the size of two 123 cells and work well in some LED lights that use two disposable 123 cells. I have been using the Pila version of these cells for about five years in my SureFire L4 LED light and have now bought four more cells for other flashlights. These are available from 4Sevens (USA) as well as other places such as www.dealextreme.com. Make sure you get the protected cells.

At some point, this tape was played on a 1/4-track machine that injected hum onto the left channel. Here’s what the magnetic viewer showed:

At the very top we can see a remnant of the left channel material, then the 120-Hz bars (62.5 mil spacing), then the remainder of the left channel material. In the middle is the guard band and at the bottom, the right channel.

Using a specially manufactured (by JRF Magnetics) assembly that contains a 4-channel 8-track head with a continuously variable height adjustment, we were able to lower the track one head to the middle of the good portion of the left channel. With that height positioning, track five’s head was well into the right channel, so we got a good transfer without the hum.

We believe this hum was written by the record head due to a malfunction in the recorder rather than an intentional erasure. If there had been an erasure, more of the left channel would have been erased and there would be a guard band between hum bars and the left channel audio as almost all erase heads were wider than the audio heads.

This type of damage is all too common using old consumer tape machines for playing tapes. I had an old junker machine in the 1960s that did this once to a tape. Unfortunately, it was also a quarter-track recording, so it was gone.

The magnetic record is fragile.

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 I installed and de-installed the head, I got to thinking that the connector might not be positioned correctly (i.e. perhaps the wrong hardware had somehow found its way into the connector mounting system.

When I measured the bottom (oriented as if the head were mounted in the machine) face of the connector mounting flange referenced to the bottom of the mounting posts (using a straight-edge across two of them), I discovered that, indeed, this connector was recessed about 25 mils (0.025″) further into the head assembly than several other ones. Adding a 25-mil thick washer should solve the problem.

This is posted in case you’re scratching your head with a similar problem. This is something I wouldn’t have immediately thought of. I don’t know if this was caused by aftermarket work or if it perhaps represents a manufacturing error.

Recently, I did a thorough search for 9 V rechargeable batteries for wireless microphones at church. I was pleased to discover that iPowerUS (they have a Toronto office) was able to provide lithium polymer 9 V batteries that far outperformed the available NiMH offerings. We bought one DC9V charger and eight DC9V-520mAh batteries for alternate use in four wireless transmitters that we use regularly. We expect this system to pay off in a year or less.

I also bought their GC-60 tester/charger for my NiMH AA and AAA cells which, so far, looks excellent. Both chargers come with a “wall wart” and a car cord.

See updates in this article.

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.

These tapes were badly warped due, most likely, to the vinegar-syndrome induced differential shrinkage. Other factors may have been poor winding during long-term storage (I had received them after several attempts to play them on another machine).

Not only was the tape cupping about its centre axis (with the basefilm shrinking so the edges were pulling back from the tape plane (away from the heads), it also had extremely wavy edges. In addition, the tapes would not lie flat on the reel due to the dimensional changes that were strongly embedded in the tapes.
We were able to play this tape on our stereo (NAB) A80, but discovered it was a 1/4 track tape (the original source had said it was half-track mono). We elected to stay with the A80 because:

• The A80 has the stabilizer roller which tends to “break the back” of cupping
• We had already adjusted the machine to have substantially higher tension to help flatten the tape–this was clearly a case of wanting the knobs to go to 11 or 12, but we had to settle for 10 on the play tensions.
• We do not have a four-track head for this machine AND the machines for which we have compatible heads do not have as easily adjustable tensions or the ability to safely set the tensions as high as we did on the A80
• The original recording was off-air AM radio after a trip of 1,000 miles through landline telco audio networks from 1964

So while the reproduction was only fair, we maintained good tape-to-head contact despite the inability to play this tape on other machines. If the content had been better fidelity and the client had been willing to pay for mounting a four-track head on the A80, we might have achieved some improved noise performance, but the original recording was quite low level (even correcting for the 1/4 track mismatch). Depending on segment, VU meter zero for the quarter track recording was somewhere around 15 nWb/m! We could hear recorded hiss,  however, over the tape noise even in this configuration!

We were able to improve listenability by using a filter that matched the playback bandwidth to the recorded bandwidth (it appeared to be about 200-3500 Hz, we filtered for 200-4000 Hz) and it sounded about as good as we would have expected hearing over a transistor radio in 1964. Further processing with Algorithmix Noise Free Pro reduced background noise (including random crowd noise, but not loud cheers–it was a football game) and made the announcers pop out more, so if someone is intent on listening to the details of what the announcers said, this would be easier to listen to, but less authentic to the sound of the original broadcast.

These tapes were transferred somewhere near their effective end-of-life. It would have been better if these tapes had been transferred 10-20 years ago. Based on other experience with Kodak tapes, I am not surprised with this. Interestingly, the Durol basefilm in its present state of decay was not translucent as most magnetic tapes are, so translucency of basefilm is not a 100% accurate test for acetate basefilm.

Aurora Cable Internet (now part of Rogers) offers a 3 Mb/s symmetical cable modem service for SoHo clients, while Teksavvy offers a DSL service where you don’t have to deal with Bell tech support (even though the service is provided by Bell). Neither service is perfect. Teksavvy generally surfs the web faster while ACI/Rogers offers the faster upload speed (by about a factor of 4) for uploading large audio files to clients (either directly or via my hosting package servers with Hostgator (my preferred hosting provider for almost three years now) or 1and1 (an OK alternate)).

I have off-and-on had the two services and struggled with Dual-WAN routers. The Hawking H2BR4 worked reasonably well, but failover (as it always is with IP service) was messy and if I used load balancing mode some websites did not like the fact that some requests came from one IP address while others came from a second IP address for the same apparent session and the web pages loaded eratically.

When I upgraded to the SoHo cable service, I added a Netgear FVS124G Dual WAN router figuring that would be typical Netgear quality, but I (and reading some online reviews it appears others as well) were disappointed.

From the beginning, I also had a Netger FVS318 which I had used in California with my cable service and it worked and continues to work like a charm. I wish I could say the same for either Dual WAN router, especially the FVS124G.

For almost two years, I ran the cable modem via the FVS124G and the DSL modem via the FVS318. I had the FVS318 set to x.x.x.1 and the FVS124G set to x.x.x.2. In that way, depending on which gateway and DNS server I selected on each computer, I could easily control from the computer which service that computer used to access the Internet.

I was never sure if it was the cable service or the FVS124G causing intermittent problems with the cable service. I recently purchased an FVS318v3 and now have that on the DSL (which I consider primary for web surfing applications) and the old FVS318 is now on the cable service and the FVS124G is in a box. So far, so good, the cable service hasn’t worked better.

I think manual failover will also be easier. We do get multiple-hour outages from time-to-time on both services, so, since most of the computers are assigned to x.x.x.1, all I need to do is swap the LAN IP addresses between the two FVS318’s and change which one has DHCP activated (for the few items that use DHCP like the security system) and I can move all the primary Internet access from DSL to cable and back. If I need to do any uploads during that time, I would manually have to change the gateway and DNS addresses for the upload computer.

Connection-wise, this is simple, I just put a short LAN cable between the two FVS318s. If we ever get a fibre to the home system with really good throughput, I’m ready as the new FVS318 has a 10/100 WAN port while the old unit has only a 10 Mb/s WAN port.

I leave this set up so that there is one cable from the FVS-318 stack to the Gigabit Ethernet switch stack, so I can easily take everything (but the security system which plugs into the FVS318V3) offline should I so wish to do that.

Speaking of the switch stack, I have a 16-port GigE switch and a second 8-port GigE switch. I use the 8-port  switch for all my 100-BaseT devices. Since the uplink to this switch is GigE, it can’t saturate with 7 100 BaseT devices connected to it. The two smaller switches were cheaper than a 24-port GigE switch. Also, I really only have a half dozen or so items with GigE NICs. While the off-site backup NAS units do have GigE ports I’ve never bothered to update the media converters on the fibre to GigE as on most nights the 100 Base FX link only adds about a half hour or so of file transfer time and I don’t care as I’m sleeping while that happens.

If I need to have internet access during a meeting/seminar and I want to keep people off my main LAN, I can always break away the two FVS318s from each other and let the guests use the cable service with no ties to the DSL service or our NAS units.

As a final thought, the concept of two separate gateways/firewalls on the same network segment was the big gestalt to me when I realized I could just tell each computer which one to look at and I could swap which service was primary by just changing the gateway’s IP address, this all fell into place.

Please note that connecting any microphone other than the intended one to any of the adapters shown in the link may severely damage the microphone. In general, while the vast majority of dynamic microphones and some ribbon microphones can work with phantom powering, it is a good idea not to send power to microphones that don’t need it.

In the 1960s, transistorized microphones from AKG, Neumann, Schoeps, and Sennheiser became available. There are several niches of early microphone powering that continued on for many years. Perhaps the easiest way to look at it is backwards.

I have adopted the terminology “hot” and “low” to refer to the audio signals in a balanced line. Hot is defined as the voltage going positive in respect to the low lead with a positive pressure at the microphone diaphragm. I’m using “hot” in this context rather than “hi” because so many people have heard of “pin two hot” or “pin three hot” that I wanted to be consistent with that nomenclature.

PHANTOM POWER

Today, 48 V phantom powering is almost universal. In phantom powering the positive voltage is fed through a pair 6k81 ohm resistors, one to each modulation lead. The matching of these resistors is often done to 0.1% to maintain common mode rejection. The negative power runs on the mic shield. XLR: Pin 1-shield; Pin 2-audio hot, +48 V; Pin 3-audio low, +48 V. Tuchel: Pin 1-audio hot, +48 V; Pin 2-shield; Pin 3-audio low, +48 V. This was standardized in the 1960s in DIN Standard 45596.

A caveat about phantom powering voltages. There are a wide range of microphones that will work with phantom voltages from 9-52 V, but many that are rated at 48 V will not work well outside of the +/- 4 V tolerance in the standard. AKG, Audio Technica, and Schoeps, for example, make many 9-52 V powered microphones, while DPA, Neumann, and Sennheiser mics generally need 48 V. Some devices (e.g. the first version of the MicroTrak digital recorder) had an odd 30 V phantom that probably worked with a number of mics, but might have degraded their performance. M-Audio took this to heart and the MicroTrak II has real 48 V phantom power. There once was a 24 V phantom power option in the standards, but apparently it was never adopted in practice and it has since disappeared.

Prior to standardization, in 1964, Schoeps produced the CMT-20 microphone which used negative 8.5 V phantom power. The CMT-200, according to Schoeps drawing SB316, dated 1964-10-14, used the same -8.5 V phantom. Later this was broadened to negative 8-12V phantom followed by the switch to positive phantom at some later point. With vintage microphones, at least from Schoeps, be very careful as they might be negative phantom.

For more details about phantom power, please see Rick Chinn’s page here. This page on Wikipedia has some further history.

NOTE: You can use a polarity-reversal cable with phantom power, but not with any of the other schema.

CAUTION: Phantom Power can damage some battery-operated microphones like the Audio Technica AT822 stereo mic. It can also damage ribbon microphones which are not floating (i.e. those that have their centre tap grounded).

T or AB POWER

Moving backwards in time, the next most widely used microphone powering scheme is called “AB power” “T-power” or “Tonader Power” and is standardized in the 1960s in DIN standard 45595. In this design, both the power and the audio are on the same wires. The hot audio and the positive power is on one conductor while the low audio and the negative power is on the other conductor. The shield is just a shield in this scheme. This was widely used by Sennheiser and Schoeps in the film industry. Neumann made a FET-70 series that used this powering scheme and many of the mics in that series are the same as the much more widely known FET-80 series (as in U-87 and KM-84, for example). Rick Chinn has more information here.

If you have T-powered microphones, you can power them off phantom power WITH THE APPROPRIATE ADAPTER.  These adapters can be purchased or made. Rick Chinn has a transformer design and a transformerless design. I developed a similar transformerless design,  but used 680R resistors instead of the 4k7 resistors that Rick used and I placed a 180 ohm resistor between the zener and the filter capacitor to reduce the noise of the zener even more.

T-Power, as introduced by Schoeps with the CT100 series in 1965 was wired to XLR connectors with the hot/+ connected to pin 3, following the Ampex standard. This polarity practice is documented on the same Schoeps drawing referenced above. Sennheiser, to the best of my knowledge, always connected the hot/+ to pin 2, which became the international standard. Many Nagra recorders came with pin 3 hot, but I believe they could be ordered either way. Sennheiser introduced this powering scheme in late 1963 based on catalog research by Lonn Henrichsen.

It got to the point where there was the term “red dot” microphones which had been rewired for pin 3 hot/+. If in doubt, this is the one legitimate use of a polarity reversal cable with T-power. Sennheiser adopted T-Power with the MKH-105/405/805 microphones in the mid 1960s. They later provided “P48″ versions of these microphones and at that point also designated the T-powered mics with a “T”. So there could be an MKH-416T and an MKH-416P48 which differed only with the powering. This appears to have been introduced with the XX6 series of microphones.

CAUTION: T-Powering WILL damage ribbon and may damage dynamic microphones.

EARLY ANOMALIES

In addition to the Schoeps NEGATIVE phantom mentioned above, Sennheiser introduced their first line of RF condenser microphones with an unbalanced, negative power connection. The MKH-104/404/804 have odd wiring. Pin 1 of the Tuchel connector is audio output. Pin 2 is ground (audio low and power +). Pin 3 is -8 V power. This series of microphones was introduced in 1963 and discontinued between the 1968 and 1969 catalogs.

Later, Sennheiser introduced the extended-low-frequency special-purpose microphones, the MKH-110, with the same powering scheme, except Pin 3 is +8 V power!

It is trivial to power an MKH-x04 microphone from a 9 V battery, and after having noise problems with an inexpensive off-the-shelf DC-DC converter, I ended up with an alternate powering scheme, described here.

I’ve decided that this will be an application to keep in the Tuchel connector domain, so this oddball powering doesn’t get into any other microphones and possibly fry them.

CAUTION: These powering schema can damage many types of microphones.

CONCLUSIONS

While this may sound complex, in practice certain combinations of mics/recorders are used together and it’s fairly trivial to keep track of what’s what.

For example, for almost four decades, I’ve had AKG C451 microphones in my kit, and I’ve adapted almost everything to power them. Other mics that take 9-52 V phantom obviously will work there as well. I’ve had several (currently three) Sennheiser MKH-416T short shotgun mics for about a decade (I got them used). I made a P48-T12 adapter for each of them, and I keep them with the mic. When I grab the mic, I grab the adapter. Sometimes it goes right on the mic, other times it goes at the end of the first mic cable coming from the mic. Placing this at the mixer increases the risk of damaging other microphones.

When I first got the MKH-416T mics, I made a stereo powering box that had a toggle switch that could select T12 or P12 so I could use one box with a pair of short shotguns or C451s. This had unbalanced outputs (all resistor-capacitor networks, not transformers) that connected to the portable DAT Walkman recorder and used 8 AA batteries for long running time.

I recently got an AKG C460/CK63 and that’s still 9-52V.

Some of the newer mics in my collection (Neumann TLM-103, KMS-105; DPA 4006 TL) are P48 only and, in fact, most of the new equipment I have has true 48 V powering. This includes a Sound Devices 722 portable recorder, a MOTU 828MK II multichannel FireWire audio interface for my laptop, a Mackie 1402VLZ mixer, and a Shure FP410 mixer. The church I do sound for has a Mackie 1604VLZ that I previously owned, so P48 is very common in my world. People who have used Nagras in the field report adapting everything to one scheme. In one case it was the “red dot” mentioned above.

All in all, don’t be afraid of some of the oddball powering schema, just work through what is needed. Since all of these schema are low-powered, the likelihood of any significant damage to a microphone is probably low, but still, don’t take chances with expensive, excellent performing antiques.

It is my understanding that European broadcasters at least influenced the various powering schemes by requiring compliance to their specific powering standard across several manufacturers. When I started working at ABC-TV in New York City in the early 1970s, there was a system of remotely powered microphone preamplifiers built into extended length female Cannon UA cable connectors. So this is yet another odd scheme, although it was an accessory to the microphones rather than in the microphone itself. This preamplifier was used to boost the signal level at the microphone in an attempt to overcome hum and noise on the long lines.

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Here are the ones with the picture of the chamber orchestra
http://www.richardhess.net/restoration_notes/111.jpg (red 7″)
http://www.richardhess.net/restoration_notes/120.jpg (orangy-brown 7″)
http://www.richardhess.net/restoration_notes/200.jpg (blue 7″)
http://www.richardhess.net/restoration_notes/311.jpg (grey-green 5″)

The moiré pattern you may see is the screening of the printing beating with your monitor.

These are earlier boxes for two if the above
http://www.richardhess.net/restoration_notes/111(A)_early.jpg
http://www.richardhess.net/restoration_notes/120(A)_early.jpg

And then it all became standardized in the 1970-era box
http://www.richardhess.net/restoration_notes/200_1970.jpg

When I get a chance, I’ll scan the box between the musicians one and the 1970s one.

Please remember that these modifications are provided “as is” and neither Andrew Pearson nor Richard L. Hess (owner of this site) can or will accept any responsibility for any damage, loss-of-use, or any other incident relating to this information. You may contact Andrew at    Andrew(dot)Pearson(at)bl(dot)uk

RE: Clock and other digital noise on the Studer A807

I managed to reduce the 9.6kHz contribution by moving a wiring loom from the capstan servo board away from the audio boards. I discovered that sliding the audio board assembley out past the capstan board caused the interference to pass from mainly channel 2 to channel 1, as that board became closer, and discovered the source of noise in the J1 connector – ‘M3-9600′ signal. I redirected the loom up towards the spooling motors and made about 9dB improvement, although in some cases the 28.798kHz became slightly worse. However, that’s much less objectionable than the audible whistle from the 9.6kHz.

We hope to update this as we come across more types. January 2009 was, sadly, fruitful in finding at least some batch(es) of two tapes from 1990 (Agfa PEM 526) and 2003 (Emtec SM911) are degrading. The Emtec SM911 was thought to be more-or-less immune from this disease. As of this writing, it has been confirmed that batch number B0134007 was involved.

Agfa PEM-526 exhibited this odd behaviour. The tape was recorded in 1990.

There is also a discussion about PEM-469 showing similar behaviour here.

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

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.