Subject:OT: Cassette Tape Problem

Posted by: RalphM

Date:5/19/2008 8:58:55 AM

I have two cassette tapes that people have asked me to transfer to CD. (No copyright problems here). Both are showing the same problem wherein the tape begins to slow noticeably about half way through. This is the same on two different tape decks.

On the first tape, I've gone so far as to transfer the tape reels to another casette shell with the same results. The tapes are from two different sources and were professionally recorded, so I don't think there is a problem with the original recording equipment.

Any ideas as to what could be causing this?

Thanks,

RalphM

Subject:RE: OT: Cassette Tape Problem

Reply by: Chienworks

Date:5/19/2008 11:41:25 AM

Well, except that you say "professionally recorded", i would guess that the original record deck was rim drive rather than capstan drive. This is generally a feature of ancient dirt-cheap decks used primarily for dictation and is very very rare in cassettes. But, the point is that rim drive machines spin the takeup spool at a constant speed. As the spool fills the tape moves faster and faster. When you play such a tape back on a capstan drive deck then the parts recorded faster fill play back slower.

I actually had one of these given to me last year to transfer to CD. There wasn't much mechanically i could do except to transfer the recording as it was to digital. Then in Sound Forge i played with Effects / Pitch bend, using my best guesses as to what sounded right, to try to restore the correct speed. The client was delighted! He had only thought he would get a CD of what he had heard, which was the sound gradually slowing down. He never expected i'd be able to fix it as well.

Subject:RE: OT: Cassette Tape Problem

Reply by: musicvid10

Date:5/19/2008 6:07:56 PM

I've never heard of a cassette transport without a capstan, and even if they were dubbed from R2R, capstan drive was the norm by about 1960, so I'm guessing any of three factors or in combination (all pretty common):

1) Capstan slip in the recording. This would create lots of "wow" in the program as well.

2) Stretched tape from overplaying or improper tensioning. Not much you can do about this.

3) Sluggish cassette from disuse. FF the cassette to the end, then Rewind. Do this a couple of times and see if it frees up.

Other than that, it would be a guessing game to try to compensate in SF or Vegas without some kind of reference.

Subject:RE: OT: Cassette Tape Problem

Reply by: RalphM

Date:5/19/2008 7:12:27 PM

Kelly, I have seen tapes from the rim drive units that you mentioned. They were used mostly for voice note taking. These tapes are definitely not of that type.

Musicvid, the stretching possibility is intriguing. I've considered cutting one of these tapes half way through, putting a leader on it and seeing if the slowdown is still there.

I've also thought of putting some silicon dry lube on the mylar sheet that the tape lays on during playing. However, these are not my tapes, so I'm reluctant to get overly aggressive.

RalphM

Subject:RE: OT: Cassette Tape Problem

Reply by: Chienworks

Date:5/19/2008 7:37:40 PM

Well, whatever the physical cause, pitch bend should be able to deal with it. You can set control points to make a varying speed envelope, so you can adjust the entire recording in one swoop. No need to split it up into different sections. It just takes a lot of trial and error to get it right.

Subject:RE: OT: Cassette Tape Problem

Reply by: rraud

Date:5/20/2008 4:49:29 PM

Some old (and not so old) reel to reel tapes have a 'shedding" problem that would gunk up the transport path, causing slowing and even stoppage, however I have never experienced that with cassettes. However that's something to check.
If this was an issue in recording, another option is a playback deck with a pitch control, you may be able to compensate by gradually increasing the PB speed.

Subject:RE: OT: Cassette Tape Problem

Reply by: RalphM

Date:5/20/2008 7:43:11 PM

I'll try the pitch bend approach. Would be great if the slow down were linear - will see.

Unfortunately, I don't have access to a cassette player with pitch control, but that would be great since my sense of tempo is pretty good.

Thanks,
RalphM

Subject:RE: OT: Cassette Tape Problem

Reply by: Jay Z

Date:5/21/2008 7:38:26 PM

Sounds like you have cassettes that are suffering from archival shed syndrome, commonly refered to as sticky shed. What happens is, the binders over a period of time absorb humidity from the atmosphere and a chemical reaction called hydrolysis occurs , which results in a breakdown of the binders. This causes layer to layer adhesion, and/or the "sticky shed" that causes the friction that slows down the tape transport. Usually seen on open reel tapes with back-coating, professional cassettes can do this also as they too usually have backcoat.

It CAN be fixed to make the tapes playable. The recomendation is to have your deck completely cleaned and set-up for transfer into your DAW on the first pass after treatment of the tapes so that your potential for loss of high frequency component is minimized. The tapes will actually be good for several passes, for several weeks but it's generally best to do it on the first pass.

Here's what you do...

Carefully open up the cassettes (assuming the shells are screwed together...If sonically welded together, you can still treat the tapes using the process outlined below, but your sucess might be marginal. Place the tape spools inside the "oven" you have, or will create with the instructions below.

Ideally, you'll have a convection oven lying around (ha!), but assuming you do not, you need to emulate one. DO NOT USE A RADIANT HEAT OVEN OR MICROWAVE, IT WILL DESTROY THE TAPE AND/OR RUIN THE PLASTICS....READ MELT!

Take a cardboard box open on one end...Turn it upside down and support it so that it is about an inch or two above the table surface. Punch a hole in the side of the box big enough for the business end of a hand-held hair dryer to stick into.

Punch a meat thermometor through the other side of the box and adjust the temperature of the air inside the box by adjusting the temperature of the hair dryer either by it's own control, or by adjusting the height of the box above the table. Set the STABLE inside temperature of this "make-shift oven" for 130 degrees farenheit. DO NOT ALLOW IT TO GO ABOVE 135 DEGREES or you can warp the basefilm...Letting it fall below 125 degrees, and the treatment may not be as effective...Use a high fan speed to keep the hot air moving.

Once you have calibrated the "oven", place the tape spools inside and bake for 8 hrs. After the tape has baked for 8 hrs, remove them from the box and allow them to sit at room temperature for 24 hrs. This allows the binders time to re-adhere to the oxides and basefilms. If you fail to let the tapes cool properly, you can ruin them, so let them cool...PLEASE.

After the 24hr cooling period, re-assemble the cassettes, and they should be playable, essentially like new.

A note: The less you do to the tapes before treating them the better. The more you try to play them, the physical positioning of the oxides that contain the magnetisim gets moved around because the binders have let go...Treating the tape causes the binders to re-form, and glue the oxides back into position.

If you've messed with it too much, on playback you will notice a definate roll-off of the high end (because of the displaced, short-wavelength oxides)...All is not lost though, you can usually EQ the high end enough to make up for it...Remember, you're dealing with cassettes, whose frequency response is limited to begin with.

This formula is the same formula that I have personally used on a couple thousand professionally mastered reels of tape (and cassettes), sent to me for treatment by major recording studios when I was the Senior Product Support Engineer for Ampex Recording Media when I was based in the Chicago regional field office, so I know the process works. I personally used a convection oven, but the box idea came from Cris Stone at The Record Plant in L.A. (all courtesies extended), as was detailed in an issue of Mix magazine many, many moons ago.

Good Luck....

Subject:RE: OT: Cassette Tape Problem

Reply by: RalphM

Date:5/23/2008 9:21:48 AM

Thanks Jay Z,

I wish these were my tapes because the procedure you describe is scary. It certainly does match the symptoms I'm seeing however, si there is probably nothing to be lost by trying.

Now all I have to do is convince my wife to let me use the oven for the whole day ;-)

Subject:RE: OT: Cassette Tape Problem

Reply by: Jay Z

Date:5/26/2008 7:46:36 AM

Unless it is a convection oven, that is one that cooks with heated air, DO NOT USE IT...Typical house ovens or stoves use radiant heat...For example, the temperature inside a steak cooking in an oven can and will increase above the temperature the oven is set to because of the radiant heat. Convection ovens have the heating element outside the cooking chamber, and blow the hot air into the cavity.

It is scarry the first time you do it, but as I stated, I've done thousands of tapes...Many for noted artists re-mastering their old stuff for re-release, as well as instrumentation and logging tapes for the federal governmment...(did you know that EVERY phone call in the Washington DC area is recorded?)...

Just keep an eye on the temperature with the meat thermometor and you'll be fine...The cardboard box method actually works very well if you don't have an oven...

I did have some customers in the Houston area that told me one time..."Well shoot boy...Any time I have that problem, I just put the tapes in the back window of my car on a hot day and let 'em sit for the day, and run 'em the next day". Now to me, THAT is scarry...irreplaceable masters melting in a car...How do you explain that to the client?

Good luck with the project!

Subject:RE: OT: Cassette Tape Problem

Reply by: RalphM

Date:5/26/2008 8:02:12 AM

I do have a convection oven and a meat thermometer with a remote display unit, so I should be able to control the temp just fine. Maybe I could bake a cake at the same time to save on energy....

I've lived in the DC suburbs for 40 years. Guess none of my conversations were ever interesting enough to get an "interview."

I'm at the beach this weekend - will let you know how this turns out.

Thanks,
Ralph

Subject:RE: OT: Cassette Tape Problem

Reply by: jackn2mpu

Date:5/27/2008 11:37:32 AM

Jay Z said:

Unless it is a convection oven, that is one that cooks with heated air, DO NOT USE IT...Typical house ovens or stoves use radiant heat...For example, the temperature inside a steak cooking in an oven can and will increase above the temperature the oven is set to because of the radiant heat. Convection ovens have the heating element outside the cooking chamber, and blow the hot air into the cavity.

I replied:
Convection ovens, at least home ones, do NOT have their heat source outside the cooking chamber. What makes an oven a convection oven is just a fan that recirculates the heat in the oven. The only convection oven that would have the heat source outside the cooking cavity is a microwave convection oven.

Jack

Subject:RE: OT: Cassette Tape Problem

Reply by: Jay Z

Date:5/27/2008 2:17:49 PM

Jack:

Well...Not the one I used, it definately was not a micro-wave...But then again, it was a commercial oven, not a home unit; so I can't speak to the home variety.

The point is, to work with the heated air, and not the radiant heat...Hopefully he understands this, it sounds like he does. The process works quite well, and the archival situation has generated a lot of questions and controversy over the years...

Many people claimed that it was "only Ampex" that had the problem...Not true...I've fixed tapes from every manufacturer...The only reason it seemed like "only Ampex" had the problem, was because they had 95% of the market...With that much product out there, it makes sense that it would seem that way, as the majority of the tape you would see would be Ampex.

Now that the tape format is essentially dead, I'm waiting to see what archival problems crop up now with optical, hard disc & flash media...It should be real interesting...

Hopefully, he'll come back and report success with his project...I rarely give out the formula on-line as you have no control over how the person actually does the process. We used to have the customers sign releases before we would even touch their tapes...Liability and all that, the legal beagles always wanted something in writting...

Cheers!

Subject:RE: OT: Cassette Tape Problem

Reply by: Geoff_Wood

Date:5/27/2008 7:43:13 PM

Those thermostats are crude, and the the thermal inertia of a domestic oven pretty much ensures that you are likely to melt something.

Use a food dehydrator - these can be set very accurately to the desirable 50 degrees, with perfact constancy and stability.

geoff

Subject:RE: OT: Cassette Tape Problem

Reply by: Jay Z

Date:5/28/2008 9:04:42 AM

For clarification...the temperature needs to be 130 degrees farenheit...

Subject:RE: OT: Cassette Tape Problem

Reply by: Geoff_Wood

Date:5/28/2008 8:38:08 PM

Depends on what you read and where. I have had great success with 50-55 degrees (Celsius, that is, like most of the world). 130F is around 54C .

geoff

Subject:RE: OT: Cassette Tape Problem

Reply by: RalphM

Date:5/29/2008 6:57:38 PM

Well I thought this was going to be simple, but it turns out that neither the convection nor microwave/convecion ovens in our kitchen will set to a temp lower than 250 F. Guess I'll have to build the box and hair drier oven Jay Z described above.

RalphM

Subject:RE: OT: Cassette Tape Problem

Reply by: JRZ

Date:6/12/2008 10:39:38 AM

Well, after fighting for 2 weeks to get my registration problems straightened out for my software, NOW I can't login to the forum under my pervious login of JayZ...I've tried re-claiming it, but it sends the e-mail to someone else. Rather than fight for another 2 weeks, I am now logging in to the forum as JRZ...SO, any previous posts as JayZ are now being replied to by me as JRZ...Sorry for any confusion...But SCS really messed up my registrations by merging my business accounts and my personal accounts, and I guess this is a result of that.

Howsoever, I'm anxiously awaiting RalphM to post his results to the use of the process to recover his tapes, so I wanted to post something to keep this thread alive.

"Jeopardy!" music playing in the background while we wait.......

Cheers!

JRZ (formerly JayZ)

Subject:RE: OT: Cassette Tape Problem

Reply by: RalphM

Date:6/17/2008 10:03:07 AM

Sorry for the delay JRZ / JayZ.

Went from the beach to Pittsburgh to spend a week with my dad and his recovery from a perforated bowel. Sure hoping I inherited his genes for healing. At 87 he's back to almost full speed two weeks after surgery to remove a foot of his colon.

With luck the "oven" will be on the construction schedule in a few days.

Thanks for the continuing interest and help. (and the Jeopardy music as well....)

RalphM

Subject:RE: OT: Cassette Tape Problem

Reply by: JRZ

Date:6/25/2008 9:15:13 AM

Not a problem...I get busy as well...Just be sure to chime in when you get it all done...

Regards,
JRZ