Can Slow Cassette Tapes Be Repaired

Jack Endino    Producer – Engineer – Mixer – Musician – NOISEMONGER

CASSETTE TRANSFER TIPS

By Jack Endino, ©2009

I should have written this a LONG fourth dimension ago. This is aimed at the "taping and trading" community and all the engineers and producers and self-styled mastering engineers out there. As well many do not know how to extract the best quality audio from a cassette. It's super-simple but this knowledge seems subconscious for some reason. Recently a ring who shall remain nameless issued an archival CD with some bonus live material sourced from cassette. It took me well-nigh ten seconds of listening to find in that location was a trouble with the transfer on a couple of tunes, and I'm bellyaching that no 1 caught it including a well-known mastering engineer.

Here are the ii things to watch out for when using cassettes as source cloth:

1) Head azimuth mis-alignment. This means, "the playback caput should exist lined upwardly properly with the tape itself, or y'all're hosed."
2) Speed inaccuracies.

How practise you tell if there'south an azimuth problem while playing a cassette? Piece of cake. Hit the mono switch on your stereo. [Ha ha. Yes, I know. I even so have a "stereo"...] If the cymbals and high frequencies become away or it sounds all phase-ey and weird, yous have a problem. Do NOT transfer or copy that cassette nevertheless. Fixing this is easy, but you need to sympathise the why of information technology beginning. (And if you don't have a mono switch available to you for playback... yous need to go 1, or rig 1, no matter what it takes. Proffer: make a special headphone extension cable that has the left and right wires shorted together. This might blow up your stereo, but maybe non.)

Most cassette decks have two heads: an erase head, which doesn't business concern us here, and a tape/playback caput. I'm just going to call it a playback caput for at present. Cassettes contain thin record that is i/8 inch wide. The music is recorded onto the tape in two parallel stripes, for left and correct channels. The 2 stripes have up 1 one-half the width of the tape; this is then you can 'flip the cassette over' and tape the 2 stripes again on the other half of the tape. (Note: other Half, not other SIDE.) So, technically in that location are four tracks on a cassette tape: side A, left-correct, is one half the tape width, side B (with the tape running the other management) is the other half. The playback head looks like it's the full width of the tape, only it has two tiny magnetic pickups in it that merely take upwards half its width. These pickups, like tiny guitar pickups, are nether only one half of the tape, positioned so that they line upward with the two recorded stripes at that place. They "read" the music off the tape. Y'all flip the tape over, tape goes the other management, and at present the other ii stripes are over these "pickups", and side B plays.

The trouble arises when a playback head is not aligned exactly with those magnetic stripes going by. The result is that a cassette that sounds fine on one cassette deck may sound muffled or otherwise weird on another one. Yous've all heard this. A cassette often sounds the all-time played back on the aforementioned deck it was recorded on. Put it in a different deck, and the tape and the caput may no longer line up besides.

Why? Cassette decks were super-cheap consumer products full of tiny moving parts. After a couple years of wear and tear, the alignments of those parts drift. The manufacturing tolerances were never that good to begin with, and then these parts article of clothing downwardly, aggrandize and contract, or shift slightly with historic period or just beingness banged around over the years. This mis-alignment problem between different cassette decks is not just common, information technology's UNIVERSAL. Expect information technology.

ADJUSTING AZIMUTH FOR A Item Record

This is very difficult with a boombox-type cassette deck, but you have no business making of import transfers off archival cassettes with a nail box.

You lot need a typical front-loading, gratuitous-standing cassette deck, where the door opens out at a camber, you skid the cassette in more or less vertically, and push the door closed. Nakamichis are good. (Past the manner, make clean the heads and rollers with booze and a Q-tip before you do this, just to remove another possible variable.) The playback head is usually at the bottom center. Look downwards and you'll see it. The diagram I've made shows such a view of the playback head "from above". When you drop the tape in and hit "play," the caput moves up about a quarter-inch and pokes into the cassette vanquish, making contact with the tape.

Meet if y'all can effigy out how to remove the front embrace on the "door". Most of them are designed to exist removed hands so a tech tin get at the playback head while a cassette is actually playing. Sometimes it's a couple screws simply usually the comprehend just snaps into identify, and volition slide upwards and out with a skillful tug. You may have to monkey with information technology to figure this out, there may be hidden tabs to printing, etc. If y'all interruption it, don't come up crying to me. Once you get the outer cover to come up off, y'all should see the playback head clearly in front end of you, below the record. The erase caput will be to the left: a smaller caput, sometimes black in colour. To the right will be the rubber compression roller and the capstan, the tiny rod that turns and pulls the record past the heads.

Examine the playback head, in the centre. You should see that information technology is mounted with two screws, 1 on each side. The i on the right has a solid post nether it, and should exist screwed tight. But the ane on the left might have a spring nether it, allowing it to be turned in and out a bit. This is the "azimuth adjustment screw". If you lot plough it with a tiny screwdriver, the head volition movement in and out, toward you and abroad from you. And actually, since the screw on the right is not moving, the head actually flexes on its backplate side by side to that screw ever so slightly equally information technology moves in and out... so actually, only the left side of the caput, equally you wait at information technology, is moving in and out. That means the head is also twisting at a very slight angle to the tape. This is key.

Often, you lot will see what looks similar a chunk of colored clear glue dabbed onto that left spiral. They put that on there at the factory to hold the azimuth screw in identify after the initial adjustment was made, earlier the new cassette deck was shipped to the dealer. Ignore it... fleck information technology off with the screwdriver, or just break it loose when you turn the screw. You are trying to transfer a tape here... it'south that tape you lot have in front of you that matters in this case, non the original factory alignment. You lot accept to adjust the machine for THIS tape, right at present.

These diagrams evidence what happens it the azimuth is wrong. Not only does the tape non pass exactly over the pickups, which in itself causes massive loss of high frequencies (and some overall volume loss), but the pickups themselves are not perpendicular to the tape. Note the slight angle. It ways i channel is delayed slightly. That'due south a tiny deviation, but the distance involved is ofttimes longer than a wavelength of the loftier frequencies on the tape! Result: when you lot heed in mono, the high frequencies abolish out or sound "phase-ey." (Techical term: "comb-filtering.")

To fix it and so a given record plays back at its best, put the tape in, find a passage on it with a lot of cymbals or other high-frequency content, and switch your playback system to "mono". Headphones are crucial here. While the tape is playing, reach in advisedly with a tiny screwdriver, and adjust that LEFT screw (the 1 with the spring) on the playback caput in and out, peradventure one-half a turn dorsum and forth, and mind to what it does to the sound. The correct adjustment is when you hear the well-nigh bright, crisp point. You'll encounter that if you plough the screw away from that point in either direction, the sound gets duller and more than phase-ey sounding. This is not subtle at all; the correct setting volition be extremely obvious. And so switch information technology dorsum to stereo. You take now gotten it to sound as skilful as information technology's going to.

If yous are listening in stereo, Not mono, you won't be able to get it exact plenty. Without the ii channels combining and making that phase-canceling sound, you won't be able to hear what's going on. You might get it in the ball park, but the improvement when adjusting it while listening in mono is DRAMATIC.

I can't stress enough how easy this is.

WHAT IF IT'S Besides Tardily?

What if someone gives you digital files that were transferred from a cassette, and you listen in mono and at that place's that unmistakable phase-ey audio? If you don't take the original cassette, tin y'all gear up it?

Somewhat, yes. You can set up the delay office of information technology, and compensate for the rest with EQ. Bold you have access to some digital sound programme that allows you to view the waveforms up shut, load the files into your programme, and zoom in with as much detail as y'all can. You lot will run into that one side is slightly behind the other. It may exist merely three or iv samples, or a lot more. Four samples may not sound similar much, but it'southward easy to hear when you hit the "mono" switch. Figure out a style to nudge one aqueduct, a sample at a time, until it lines up visually with the other channel. Mind in "mono," and the improvement will be obvious. Now you lot've canceled the "filibuster" upshot of the azimuth Bending being wrong, with the head being slightly twisted when the tape was transferred to digital. Add some high end EQ, and you can compensate a fleck for the rest of the upshot of the misalignment, although y'all volition increase the tape hiss a lot, which can't be helped. Select/export/bounce/render the new file, and you're washed.

SPEED ADJUSTMENT (Alert: HIGH VOLTAGES PRESENT!)

WARNING: y'all can't do what I'yard near to draw without taking the top encompass off your cassette deck and exposing the innards, and so mucking around inside information technology WHILE THE Ability IS ON. THE POWER SUPPLY FOR THE DECK Volition BE EXPOSED. THE Air-conditioning LINE VOLTAGE CAN KILL YOU. YOU SHOULD HAVE A QUALIFIED TECHNICIAN Practise THIS FOR Yous. THE Post-obit IS FOR EDUCATIONAL PURPOSES Simply.

Cassette decks are terrible nigh speed accuracy. This drove me crazy for years. Their speed changes with fourth dimension and wear. Often there will exist a 2 or 3 percent speed difference between unlike cassette decks, or between a deck when new and that SAME deck a yr later. Three percent may non sound like much, but remember that 6 per centum equals a half-pace or semitone... that's the next fret on a guitar, or the side by side piano primal. So, i percentage (one-Sixth of a half-step) is a pretty big deviation in pitch and speed, and is very piece of cake to hear and feel.

Cassette decks mostly have petty 12 volt DC motors in them. Sometimes one motor does the task of turning everything: capstan, take-upward reel spindle, rewind/fast forward, etc. On meliorate decks, in that location is a motor for the capstan, and a separate motor for everything else. We are concerned here with whatever motor controls the capstan and thus the tape speed. The motor itself usually has a tiny pigsty somewhere in dorsum of it, usually with a tiny condom flap to seal out dust. Inside that hole will oft be a very tiny aligning pot with a piffling slot in it for a tiny screwdriver. If you achieve into that hole with the screwdriver, you will notice the slot, and if you plough it while playing a tape, you volition hear the tape speed get up and downwards. (If you bear on the shaft of the screwdriver against the side of the pigsty, you may hear wild speed fluctuations, because you lot are shorting the adjustment pot to basis. My screwdriver is wrapped with a little piece of record to avert this.) You lot won't hurt the motor by doing this, so don't be agape of it. Simply... exist actually careful non to touch anything else inside the deck, as you can electrocute yourself! You lot will be extremely dead! DISCLAIMER: THERE ARE VOLTAGES NEARBY THAT Tin can KILL YOU! PROCEED AT YOUR OWN RISK! Have A QUALIFIED TECHNICIAN Practise THIS FOR You lot! THIS IS FOR EDUCATIONAL PURPOSES ONLY!

How do you know when the deck is at the correct speed? You demand a reference. I spent 60 bucks on a "Cassette Speed Reference Tape" which has test tones on it, at exact known freqencies. (Google "Magnetic Reference Laboratories.") Then I spent 250 bucks on a "Frequency Counter." (Google "Total Compass Systems" or "Sweetwater Sound." So try "Loftech TS-1.") You feed a pure tone into it, and it gives you lot a numerical readout of the frequency. You put the exam tape in the deck, connect a guitar cable from the cassette deck'southward headphone output into the frequency counter, use the tiny screwdriver in the adjustment pigsty on the back of the piddling DC motor, and accommodate it while the examination tape plays until the counter reads correctly.

Here's a question: how can you get the tape speed of a playback deck to be the same equally the deck that recorded the tape you lot're trying to play? To make your transfer as perfect as possible, yous want the speed of the playback deck to lucifer the speed of the deck the tape was recorded on, merely like how you matched the head azimuth. Unfortunately, unlike with azimuth, with speed you lot can't tell exactly. If you know a song is in a particular musical fundamental, you can play guitar or piano along with the record and accommodate the speed by ear until the tuning sounds right... except that oftentimes, the tuning on the tape is not what you think it is. (Read my guitar tuning article, and cry.) Guitars may be slightly sharp, in which case you may inadvertently make the tape run besides deadening. (Etc.) My philosophy is, getting the playback deck back to the standard, correct playback speed is Nigh Likely to brand About tapes play back the all-time, on average, and that's the best yous tin practice! It's also the just manner of making sure tapes you record on THAT car will play dorsum correctly in the time to come on the largest number of other machines. There are always TWO variables here: the speed of the playback deck in front of y'all, and the speed of any deck RECORDED the record you lot're now playing back. Merely you can merely right ONE of these variables, the deck in front of you, and then you might as well just do it... remove 1 of the variables.

(I can imagine 1 other thing that I oasis't tried. If you could detect whatever 60 cycle hum that was recorded on the tape forth with the music, maybe guitar buzz before a song, y'all might exist able to employ that as a reference. Buzz and hum is usually a mix of 60 Hz and its harmonics like 120 Hz, 180 Hz, 240 Hz, etc.... unless the music was from Europe, where line frequency is 50 Hz... oh, heck, never mind.)

Since you lot don't want to spend all that money, I'll tell yous the "guerrilla" method of doing this that I figured out when I was sixteen. I tried two assumptions: that a cassette deck when NEW was probably running at the right speed, and that a pre-recorded commercial record of any popular album was also probably manufactured at the correct speed. I happened to have an "A 440 Hz" tuning fork. When I bought a new cassette deck, I recorded the A 440 tuning fork onto a cassette by holding the fork shut to my guitar pickup, with the guitar plugged right into the input of the record deck. So I would put the cassette into any other deck I wanted to marshal, and play the recorded tuning fork dorsum thru headphones on my head. I whacked the tuning fork and held the base of information technology against the exterior of the headphones, so I could hear information technology forth with the recorded tuning fork... and information technology was really easy to hear the "beating" sound when the speed was off, and adjust until the beating audio went abroad. I was pretty pleased with myself. Now I had two cassette decks running at the same speed. Since I was learning how to record "multitrack" by billowy signals from one cassette deck to some other with a "y" cable, having them both at the aforementioned speed was bully.

To cheque if my new "speed reference test record" really was correct, I used a "shop-bought" Led Zeppelin cassette, and a vinyl re-create of the same Zep record. My turntable (a Technics SL-23) had a super-obvious speed adjustment: it had those dots around the outside of the turntable platter, and a little orange neon strobe lite, so you could become the speed of the turntable exactly right. The trick is to cue the record and the cassette deck up to the same bespeak in the music, and start them at the aforementioned instant, and mind to see if they stay in sync for more than a few seconds. Information technology would always take a few tries before I got lucky syncing the starting point, merely it worked to show me if the cassette was running at the right speed. In case the shop-bought cassette'southward manufacturing speed wasn't authentic, I tried it with a couple other pre-recorded cassettes and vinyl records, and the results were consequent, so I knew my "A 440 tuning fork" test cassette was correct. I used that home-made test cassette and the "A" tuning fork successfully for years, until I finally sprung for the 'professional' record and gear.

Now you know what kind of a geek I already was, at historic period 16. Or was it 14?

GETTING THE AZIMUTH BACK TO "Manufacturing plant SETTING"

Pre-recorded "commercial" cassettes have another use: their azimuth is normally pretty good, on average. Suppose you desire to record some cassettes, so y'all tin listen to new records in your old Buick that simply has a cassette deck in it, like mine. To get your cassette deck (that you've just been screwing with) back to some kind of "standard" azimuth setting after y'all're washed transferring some wacko-aligned tape, go to Goodwill, Salvation Regular army or some other second-paw store and pick up a couple of Eagles and Fleetwood Mac cassettes for 25 cents. Actually, something like Metallica or Slayer that has lots of cymbals and high frequencies will piece of work even better. Strike an average between the best azimuth settings for several of these commercial cassettes, and you volition be as shut to your original "from-the-mill" azimuth setting on your cassette deck equally you will ever need to be.

Happy taping!

'Till next time,
Jack

©1997-2013 Endino

Source: http://www.endino.com/archive/cassettes.html

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