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.

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 my, 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.

In the process of doing this work, I have learned a few things which might be of assistance. This is the first post in the blog in the live sound and recording category. Many of the posts relating to microphones will also be tagged in the oral history category.

One of the challenges for good sound reinforcement or speech recording is keeping the speaker “on mic”. There are many ways of handling this, but some work better than others. Here are my favourites:

• If the room is quiet and you can do a proper setup, a pair of Sennheiser MKH-416 short shotgun mics, one for the interviewer and one for the interviewee, gives very natural and unselfconscious results.
• For larger groups, I’ve had good results with an Audio Technica AT-822 (or the phantom-powered AT-825) stereo microphone, but the actual voice quality of that mic is inferior to the MKH-416. The high-end is harsher, but, used at a greater distance that is often not as noticeable. The room needs to be very quiet for this to work well, however. This is currently my least favourite approach (of those listed).
• So far, some of the best pickup I have found is a headworn mic–the main subject of this post.

At our church, they had tried headworn mics from Shure and they really were uncomfortable. Whoever selected the units, selected dynamic units and they did not sound all that good. They were retired in favour of the Countryman E6 units (also available from Shure, although I prefer the direct-from-Countryman version with the 2mm cable for robustness).

The Countryman units were working reasonably well, but never seemed to stay in the same place. It was frustrating as it was causing a widely varying sound quality, so we decided to try a DPA 4066 headworn mic on our head priest. The results were outstanding. The unit is comfortable (no more sore ears), it stays put, and it sounds better!

It is no surprise that these are taking over the religious and theatre markets. I am not sure I’d want to try to fit one of these on 87-year-old Aunt Tilly who is trying to tell us some family histories as it may make her self conscious, but probably no more so than a large microphone stuck close to her face. That’s where the short shotgun Sennheiser MKH 416s come in handy, they get the same sound pulled farther back–as long as Aunt Tilly talks in that direction.

As mentioned in a recent post about Story Corps, it appears they are using the Neumann KMS-105 in their mobile recording units. These are reputedly also excellent microphones and would be worthy of consideration when a more conventional, close-talking microphone is required.

A clip-on lavaliere microphone (such as the DPA 4060 miniature microphone, essentially the same capsule as on the 4066 headworn microphone) is useful, but the positioning is critical and often the sound is not as good as one would hope due to body resonances and clothing absorption and rustling.

This monitoring topology is actually identical to two 1-inch 40-channel reel-to-reel logging machines I have where one can listen to any combination of one through forty tracks on a single output.

The solution for the reel machine is that I have about half figured out how to create 40 different outputs–and then I have to figure how to digitize 40 channels simultaneously. All can be overcome, but the cost to do it generally terminates the inquiry.

Fortunately, there is a solution for the 4-track cassette machines: use the higher-quality 4-track machines designed for music recording. I have a Tascam 234 (as well as a 238 8-track unit). Yes, I know these operate at 3-3/4 in/s while the logging recorders are running at 15/16 in/s (normal cassettes are in the middle at 1-7/8 in/s).

What I do is record the four tracks playing at 3-3/4 in/s into the computer at 88,200 samples/second (s/s). In samplitude, after the recording is made, I make a new virtual project that has a project sample rate of 44,100 s/s. I load the tracks into that. I then adjust all four tracks to -50% speed in the object properties panel. I use resampling for highest quality. This provides a 1/4-speed playback of the original files while maintaining a 44,100 s/s output file.

The digital data, of course, is actually at some point being processed at 22,050 s/s, placing the Nyquist frequency at 11,025 kHz, for an effective bandwidth of perhaps 10 kHz.

But, that isn’t a problem as only a very few Nakamichi cassette recorders ever made better than 10 kHz at 15/16 in/s — this wasn’t even officially in the Philips standard.

So, there you have a way to migrate these recordings into 44,100 ks/s WAV files while doing the bulk of the work in 4x real time.

You may add equalization and other filtering to improve the usually poor sound after the output is at the correct speed.

I actually had to put the recordings back on this infernal format after repair of the defect (very poor recording speed due to a broken machine), so I reversed the process with the Tascam 234 without adding any equalization and the client was apparently happy (I received payment and no feedback).
As an alternate to the speed/pitch adjustment in the virtual project, one could bounce the 88,200 s/s track played at 44,100 s/s to a second 88,200 s/s track and then repeat the process of loading that as a 44,100 s/s file and it will be in time. I prefer the single-pass approach that I can do in Samplitude.

One of the things that affects my procedure is that my audio interface (RME Multiface) does not work below 44,100 s/s.

Good 4-track recorders like the 234 have not been made for a while. Find them while you can.

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.

The recent experience: A client project generated about 70 GB of files so hard-drive delivery made sense–especially since I had two gently used Western Digital Passport 80 GB drives sitting on the shelf. There would be no infant mortality here. The client (on one continent) and the producer (on another continent) were both to receive copies. I shipped them off and the producer (on the same continent as I) received his copy first and mentioned to the client he couldn’t read it on his Mac. The client had told me he was sure that the Mac would read NTFS, so based on my conversation with Eric, I decided, with client approval, to send NTFS. A few days later, the client received his copy and is pleased with the files and was able to open them without a hitch on his Mac.

As of this writing, the issue of the producer’s disk is still up in the air. I have offered to take it back, reformat it as FAT32, reload the files with MD5 checksums, verify the checksums, and return the drive to him. I think the producer is looking for a Mac utility that will permit reading the disk as-is. I hope so, less work here, but still I’m willing to undertake this to maintain client satisfaction.

In the meantime, I was searching for an easy way to format a drive larger than 32 GB in FAT32 which is locked out by design in Windows XP. It turns out that there is a DOS-box utility, FAT32FORMAT, that works like a charm. If the drives are combo USB/FireWire, using the Sound Devices 722 to format them would be a choice, but for USB-only drives, that is not an available option. PLEASE be careful as this utility will destroy all data on the disk. Use it with care.

In the early days, apparently wire recorders used bias as low as 30-40 kc, but Jay McKnight recalled in the pre-Ampex days, 60 kHz was common.

The Ampex Standard was 100 kc up to the MR-70.

With the MR-70, Ampex switched to 150 kHz bias frequency (and adopted the Hz) [Larry Miller, ex Ampex]

Other later machines used different bias and erase frequencies. We can see with a few exceptions, the top bias frequencies were commonly limited to 250 kHz for audio, with the Sony APR series and the Ampex ATR series in the 400 kHz region. For cassettes, a practical maximum appears to be about 150 kHz.

Ampex AG-440 (A) stayed with 150 kHz [manual]
Ampex ATR-100 144 kHz erase, 432 kHz bias (1:3) [manual]

MCI JH-24 Multitrack 210 kHz bias, 105 kHz erase [manual via Brian Roth]

Otari MTR-10/12 II Bias 250 kHz (erase not spec’d) [manual]
Otari MTR-90 (original) 246 kHz bias, 123 kHz erase [manual via Brian Roth]

Sony APR-5000, APR-24 100 kHz erase, 400 kHz bias (1:4) [manual]

Studer A80VU 80 kHz erase, 240 kHz bias (1:3) [manual]
Studer A80 RC 150 kHz [manual]
Studer A810, A807, A820 2CH 153.6 kHz [manual]
Studer B67 150 kHz [manual]
ReVox A77 120 kHz [manual]
ReVox B77 150 kHz [manual]
ReVox PR99 150 kHz [manual]

Tascam 32/44-OB — 150kHz [manual via Tom Fine]

Technics 1500/1506/1520 — 120kHz [manual via Tom Fine]

Here is a quick sampling of published bias frequencies for two top-of-the line cassette recorders, a better-than-average portable, and an early compact portable.

Nakamichi Dragon (Along with the Nakamichi CR-7A, perhaps the finest machines ever made for overall audio quality) 105kHz (Service manual dated 1985 (scan) 1990 (copy))
Nakamichi MR-1 — 105kHz [manual via Tom Fine]

Studer A710 (a high-end cassette recorder, without the auto-azimuth that makes the Dragon superior) 150kHz (no date, scan on Studer ftp site)

Sony TC-D5M (a workhorse, good quality stereo portable) 85 kHz (Svc Manual dated 1980)
Sony TC-55 (an early compact — jacket pocket — mono portable) 41kHz (as low as I’ve ever seen) (Svc Manual dated 1972)

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.

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.

I use paper leader tape as I’ve seen too many tapes damaged by the oxide adhering/laminating to plastic leader. I also don’t know where to get any more of this as I’ve laid in a large supply of this as well. Sorry.

Edi-Tall blocks are also out of production, sadly. They show up on eBay from time to time.

The splicing angle for new cuts is not all that important, but the angles were used to minimize disturbance and to provide a short crossfade at the splice (I used to hand-draw dovetail splices that were about an inch long to make the crossfade work in stereo).

The “MTA” or minimum track angle blocks for multi-track tapes were based on the speed of the tape and how much of a scatter was acceptable between the tracks as the splice rolled through.

Perhaps one of the hardest Edi-Tall blocks to find is the 0.150-inch one for cassette splicing and its use is really important for that application. There are blocks that look like Edi-Talls, but are not. Edi-Tall became a part of the Xedit corporation which has morphed into making ServoReelers for hanging microphones.

These blocks aren’t EdiTalls, but they are worth the price and are way better than nothing:
http://www.tapecenter.com/tapecare.html

While on the subject of tape splicing, here are few good Web links:
http://www.aes.org/aeshc/docs/3mtape/soundtalk/soundtalkbull26.pdf

http://www.ischool.utexas.edu/~smegison/Susan/Management%20e-portfolio%20iSchool%20projects/392L%20Intro%20to%20Audio%20Preservation/Tape%20repair%20and%20splicing%20paper%20and%20manual.doc

The article also heralded this as the saviour of tape, and talked about the “old” two-track format running at 7.5 in/s — the cartridges ran at 3.75 in/s (and on some models 1.88 in/s was also available). It goes on to say later that 7.5 in/s quarter track tapes are still a high-fidelity medium. The article referred to cartridges and quarter-track reels as the “one-two punch” against stereo records which seemed to take over from the two-track pre-recorded tapes. The open-reel tape at 7.5 in/s would be the “only choice for the quality-conscious stereophile” since the cartridges were only available in 3.75 in/s versions.

There was no mention of the later name “Sound Tape” in the article, but that appears to be the semi-official if not official name of this format. Thanks to Bill Schuh for that piece of information. Bill also provided a link to The Tape Place which specializes in out-of-print commercial tape releases. I have not used The Tape Place, so this is just being passed on, not a personal recommendation.

The Sound Tape cartridges used the standard 1/4-track interleaved format which prevailed for a decade as the consumer open-reel format.

Details about these formats can be found here and here in the Formats and Resources subset of this website.

“You may also be encountering JIS (Japanese Industrial Standard, IIRC) crosspoint (not sure if “Phillips” is correct here, although people do say it) screws. These are a bit different than a standard Phillips, but don’t necessarily have telltale markings. One dot between two slots and near the center is the potential marking that I’m aware of. This is part of why I think you may be seeing JIS, not PoziDriv:
http://realbig.com/miata/1999-09/2918.html

“I just encountered, AFAIK, my first PoziDriv’s, on a Maxtor HD.

“You might encounter these on Japanese-made RC vehicles (helicopters), cameras, print/copier machines, bike parts, (old, at least) Honda motorcycles, and probably a lot more things than people realize.

“PB Baumann (SwissTools) claims their Phillips tools are designed for DIN/ISO and JIS, but I don’t know if that’s truly possible. Hozan provides screwdrivers. Vessel (another Japanese company) makes some. Wiha, I heard, doesn’t know what JIS crosspoint is. Moody (RI company, specialize in “precision” drivers) makes some. Ames offers some. Jensen (part of Stanley?), I’ve heard does.

“Products:
http://www.heliproz.com/jisdrivers.html
http://www.escience.ca/jensen/RENDER/1/26/235/3483.html
http://www.centralhobbies.com/Tools/jis.html
http://www.ikaswebshop.com/jisphilips.html
http://amessupply.com/products1.cfm?aid=1&cid=D&sid=DE&fid=1404070

“Discussions:
(there is useful information in here, but might have to do some sifting)
http://www.mail-archive.com/pdml@pdml.net/msg211895.html
http://www.practicalmachinist.com/cgi-bin/ubbcgi/ultimatebb.cgi?ubb=get_topic;f=1;t=021387;p=0
http://www.runryder.com/helicopter/t136466p1/
http://support.conurus.com/viewtopic.php?t=10
http://www.instructables.com/id/Enhance-the-functionality-of-many-screwdrivers./

“I hope that this helps.”

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.

I have two Studer A80s that I use for high-quality master tape transfers. They are not equipped to handle the speeds and track formats found in most of my oral history work. As I delve into a large oral history project, I found I needed more work space, and didn’t have much room to store the A80s elsewhere.

I asked my handyman who helped me build the studio in 2005 to make me two A80 covers. We sketched them up and a few days later he brought them over. The exterior wrap-around is solid oak 1×6s. The top is 3/4 inch oak veneer plywood set in. Inside, there are 1×4 poplar strips running around that rest on the A80 frame and against the top. These were glued in and the glue holds the top in. Only the frame is screwed together. We opted not to bother hiding the screws. Presented as a hopefully creative solution as space utilization is always a challenge.

As to the Racal Store 4DS instrumentation recorder shown on top of this A80, please read this post:
http://richardhess.com/notes/2008/01/09/using-the-proper-toolsand-dont-try-this-at-home/

I was getting rather frustrated and since it was a four-track tape and one of the techniques that is supposed to reduce squeal is to play the tape faster, I dragged out my Racal Store 4DS instrumentation recorder which has a 75,000 Hz bandwidth at 15 in/s and played it at 15 in/s and digitized it at 88,200 samples per second. After slowing it down 4x and ending up with a 10 kHz bandwidth (which I subsequently truncated to 5 kHz since there was no useful information above that, but lots of noise–same as the non-squealing portion of the real-time transfers on a Studer A810).

Why did it work? — That is the big question. I suspect lower tape tensions than even the reduced-tension settings on the A810 and different head geometry were major factors, plus overall shorter unsupported tape spans, and few stationary objects contacting the heads, but there was still an erase and record head which had been removed from the A810. I think that the 4x speedup helped greatly. I also turned up the outside air (how I cool the studio in the winter–I like my fresh air this way–in the summer, of course, it’s connected to the central air conditioner) which kept the tape and recorder cool. I also think that the Racal Store 4DS doesn’t heat the tape and head assembly as much as most pro audio recorders do.

I received great support and wonderful ideas on both the Ampex and Studer mailing lists. Special thanks are due Jay McKnight who has been a supporter of speeding up the tape to eliminate squeal (which is really stick-slip and causes frequency modulation of the audio). I had avoided the 4x speedup on the A810 because of the signal electronics bandwidth limitations. While in this case, 20 kHz would work fine, I wanted to digitize with 40 kHz bandwidth to make sure I wasn’t losing any highs.

There may be room for misunderstanding as to the precise topology of the Racal Store 4DS tape path. Here is a brief explanation. The tape comes off the top of the supply reel and around the top-mounted tension sensor which is a roller. The tape then is unsupported from that roller until it enters the head area. The large diameter device at the top of the head area is merely a tape guide. It is both a “face” and “edge” guide both in and out and does not rotate. Next the tape passes the erase and record heads on the left side. The heads are on the outside facing the centre. Then the tape turns 180 degrees around the capstan motor’s soft capstan. The capstan also drives the mechanical footage counter. As the tape heads up, it passes the reproduce head and then encounters the tape guide on the other side. It then goes over the tension roller at the top and onto the takeup reel. The reel servos are interesting as they are fast and can drive the tape in either direction. This is useful since there is no pinch roller. The photo below shows a closeup of the head area.

As an aside: you can infer from the above picture that the complement of tape machines in my studio changes. The Studer A810s in the background are being set up to record full-track mono archival reels of some cassettes.

Before running out and purchasing one of these machines, please read this post:
http://richardhess.com/notes/2008/01/09/using-the-proper-toolsand-dont-try-this-at-home/