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Digitizing Cassettes
vosnos
post Jul 24 2011, 19:52
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Hey All,

So this is my first post here and I was hoping you guys would be able to help me out with this archival/digitizing project I'm about to start. I know there have been multiple topics regarding this subject but some of them are a bit over my head and some don't exactly address my specific concerns. Unfortunately, I have absolutely no prior experience in audio engineering/modification/digitization. Anyway, I was recently given roughly 200 cassettes of bootleg concerts and my job is to digitize them as best I can. I want to preserve the quality as best I can but I have money constraints (being a college student) and so I won't be able to spend a massive amount on a top of the line tape deck (like a Nakamichi). I may also need help on remastering/editing/reformatting the tapes once they are digitized. I know I'm asking a lot but judging from the previous threads I've read, you guys are very helpful and patient. So with that said, what sort of tape deck would you suggest I get for this project? Tentatively, I think my budget would be around $300 but I may be able to spend more if it's really worth it. The cost of all the required software is also going to factor into how much I can spend on the deck. If you guys need any other background information on the cassettes (how old they are, the audio quality, etc) please don't hesitate to ask. Thank you!
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Roseval
post Jul 24 2011, 20:07
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For recording try http://audacity.sourceforge.net/
It is freeware


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AndyH-ha
post Jul 24 2011, 21:20
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There are many considerations about tape deck quality, and how it will effect the quality of your end results, perfection can be expensive. Another approach is to find a tape deck on which music sounds good to you and just use that. You should be able to capture on the computer pretty much what you hear from the deck.

Around here there are a fair number of thrift stores. I've found a number of quite useable tape decks for about $10 each. While none are what I would really like to have and use, I have still managed to get some very enjoyable CD-Rs by using them.

Thrift store purchases are pot luck but they need not be totally blind luck. Most such stores have someplace you can plug in the deck and see if it runs. Your tests there will not be the ultimate but they can give you a fighting chance.

Take a few music cassettes you can trust with you, and a decent headphone. Also maybe a blank cassette, or one you don't mind losing (in case the deck decides to eat the tape). Pre-recorded cassettes are usually sold in such stores for from $0.25 to $1.00 each. If you know the sound of the tape on some decent player, you can test to see if it sounds pretty much the same on one you are considering buying.

Beyond that, you are back to searching e-bay, or a similar site, or locating one of the used deck dealers. I don't think anything of real quality is being manufactured today.
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mixminus1
post Jul 24 2011, 22:55
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To add to what Andy said about used decks, I would strongly recommend going with a single cassette deck - dual-decks are pretty much guaranteed to be of lower quality as they were built solely for the convenience of copying.

Also, try to find one with adjustable azimuth, which is the angle of the head relative to the tape itself. This is easy to confirm as there will be two small holes in the bottom center of the door. This will allow you to tweak the azimuth for each tape in order to get the cleanest possible sound.

Yes, there are "proper" procedures for aligning azimuth to a test tape, but in your case, it's exactly the opposite: you have a large quantity of tapes from unknown sources, so all you care about is getting the best possible sound from each tape, regardless of whether or not it adheres to any "standard." As such, you'd just be tweaking by ear, and it's pretty obvious when you've hit the "sweet spot" - any adjustment in either direction will sound decidedly worse.

Edit: Oh, one more thing: look for a clean pinch roller! That's the little black rubber wheel to the right of the head. A little bit of oxide buildup is normal, but if you see a distinct brown stripe on it, it's toast, and, short of tearing the deck apart and replacing it, there's nothing you can do about it. Dirty pinch rollers will manifest themselves in major wow and flutter issues, particularly flutter.

This post has been edited by mixminus1: Jul 24 2011, 22:59


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AndyH-ha
post Jul 25 2011, 01:15
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A good single deck would be nice, a non-reversing one, single or dual, would be better, but both options are hard to find. What you get from what you find at thrift stores, which is overwhelmingly dual well reversing duping decks. might not be up to professional standards, but there may well be some such decks from which you can get satisfactory results.

Regardless of their condition, the pinch rollers will need to be cleaned fairly often. How often depends upon the condition of the tape you run over them, about which you will have no choice.

There are (used to be) professional quality tools for that sort of task but cotton q-tips and isopropyl alcohol can do a good job (90%+ concentration is best). What I've found to do a much improved job is half a q-tip (for greater rigidity) held in a pair of surgical clamps (if you can get them, obviously). These are the scissor like clamps used to hold small body parts firmly while poking around in internal cavities.

Clamp a short way behind the cotton tip and you have a stable, rigid cleaning tool. The clamp body lets you extend down into wherever you need to reach much better than trying to do it with your fingers. Needle nose pliers would probably be functional but you will have to work much harder to keep the tip firmly grasped, and the pliers will probably be balkier and harder to maneuver.
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dc2bluelight
post Jul 27 2011, 09:11
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Another important feature to look for is a deck with easily aligned play head. Since your tapes are from unknown sources, you'll probably find that they are recorded with a variety of head azimuth settings. Azimuth has a direct effect on high frequency response. Without going into the details, you can and should carefully adjust the play head azimuth to match the cassette you are digitizing for best possible response. An oscilloscope would be very helpful, not not essential. You can do it pretty well by ear with a little practice, and listening to a mono sum helps too.

If your tapes were recorded with Dolby B or C noise reduction (you need to determine this), there may be some tracking issues when using the deck's internal Dolby processing due to level mismatches. Dolby NR is an encode/decode system, the decoder must perfectly match and undo what the encoder did. Assuming you optimize response, Dolby NR also needs proper levels to track well. The only real way to do this is with an external Dolby unit that permits input level adjustment, as the internal processor adjustments are not accessible to you. You'd turn off the internal Dolby processing and use the external unit. There were several Dolby B pro units made, might find one on eBay. If the tapes are Dolby C, you're kind of stuck using the internal processing.

Good mechanical performance is important, so test for flutter and wow. Very hard to remove speed based anomalies digitally. You might also benefit from a variable speed control and use it to pitch-match the recorded material to a musical pitch reference. Many portable cassette recorders ran slightly off speed.

As to cleaning, 90% Isopropyl is good, but if you got some wood alcohol from a paint or hardware store, that's even better, and doesn't carry the risk of unknown additives. Rubbing alcohol, for example, often contains glycerine, which leaves a deposit on heads.

Dirty pinch rollers can be cleaned, but old ones may be dried out. Don't clean them with alcohol, it only dries them out more. There are cleaning solutions made for rubber pinch rollers, sorry I don't have the composition at hand, I'll look and see if I can find reference to it somewhere, or if I still have a bottle around.

High end decks of old are still good bets if they work and are in good shape. Look for something by Nakamichi, Revox, etc.
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vosnos
post Jul 29 2011, 02:08
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Hey guys, thanks so much for the replies. Sorry I haven't been able to respond, I've been so busy at work the past couple days. I really appreciate the input though. So from what I can gather, it's not necessary to buy a high end tape deck if the tapes I have are all of varying quality? They are fan-recorded bootleg concert tapes so the quality is obviously not the best. Is it fair to liken this situation to something like this: If you had a video camera that can record in 1080p but you can only show the video on a 20 year old CRT TV, what's the point in buying an HD camera in the first place? What I'm trying to say is, is it worth buying a superior tape deck when the original sound quality is already lacking?

But regardless of the quality of the deck, it should still have these features:

Single cassette deck
Adjustable azimuth
Clean pinch roller


Some questions I still have are

1). What does it mean for a deck to have an easily aligned play head?

2). What is flutter and wow?

3). What exactly are "tracking issues?" In layman's terms?

And if you guys would be so kind as to point me in the right direction to find a tape deck on eBay, that would be much appreciated. I see Nakamichi and Revox have been mentioned but I don't know if those are in my price range (?). If you know certain model off the top of your head around $150-300 I would love to hear it. As you can see I'm very lost in this search for the right deck hah. Thanks again!

This post has been edited by vosnos: Jul 29 2011, 02:09
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dc2bluelight
post Jul 29 2011, 04:26
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QUOTE (vosnos @ Jul 28 2011, 20:08) *
Some questions I still have are

1). What does it mean for a deck to have an easily aligned play head?


Most good decks had some way to adjust the azumuth of the play head. It's one of the physical adjustments of head position. See the graphic on this page:
http://www.tonmeister.ca/main/textbook/node436.html

When properly aligned to a pre-recorded tape, the gap of the head is exactly parallel with the magnetic pattern, so high frequencies are reproduced, and channel phase is maintained. When it's off, highs drop off quickly and severely, and channel phase is all over the map. Google head alignment for more detail.
QUOTE (vosnos @ Jul 28 2011, 20:08) *
2). What is flutter and wow?

Both refer to variation in linear tape speed. Wow is slow variation, flutter is rapid variation. You want a deck with the least possible of both. It's hard to test for, you need a flutter meter and a test tape to get any meaningful figures. Flutter and wow are measured in % variation of speed. Lower numbers are better.
QUOTE (vosnos @ Jul 28 2011, 20:08) *
3). What exactly are "tracking issues?" In layman's terms?

Tracking errors, when referring to noise reduction systems, refer to the decode system's ability to apply the exact inverse of what the encoder did. Dolby B noise reduction, for example, applies a variable high frequency boost during recording, then a complimentary high frequency cut during playback. However, since the amount of boost/cut is program dependent, the two ends of the system must "track" each other precisely, or audible anomalies occur, which can be overly dull sound, overly bright sound, or must a variable high end. When everything tracks, the effect is just a reduction of tape noise, no other audible effects.

QUOTE (vosnos @ Jul 28 2011, 20:08) *
And if you guys would be so kind as to point me in the right direction to find a tape deck on eBay, that would be much appreciated. I see Nakamichi and Revox have been mentioned but I don't know if those are in my price range (?). If you know certain model off the top of your head around $150-300 I would love to hear it. As you can see I'm very lost in this search for the right deck hah. Thanks again!


Pretty tough to say. Nakamichi "dragon" was good, Tascam 122B or 122C was good, so long as the capstan motor was still working right, if not, high flutter. Your budget is on the low side to get something worthy of digitizing archival material. I encourage you to use Google, and keep drilling. I found this in one quick 10 second search, it might be slightly out-dated, but seems valid:

http://www.cs.cmu.edu/~mleone/gdead/taping-guide/part1.html


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AndyH-ha
post Jul 29 2011, 05:44
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Many tape decks have openings directly in front of the head alignment screws so they are, more or less, easy to get at with a screwdriver (non-magnetized screwdriver), some don't and it can be awkward to get to the adjustment. Some use a different arrangement, such as a shaft requiring a special wrench head. Many are spring loaded to keep tension on the head, some, perhaps many, have a lock nut to fiddle with. Very often the mainly cosmetic outer cassette well cover must be removed to even see the openings.

Many people who did this work professionally put in, or had put in, a long shafted finger adjustable bolt, replacing the manufacturer's adjustment, to allow more convenient access. Perfectionists claim it is often necessary to adjust several times, or many times, during playback of each side of a cassette. If the recording decks were not too bad, you may find playback to be adequate without any adjustments. You probably do not want to make any of the other possible adjustments.

When cassettes were current and popular, I found it impossible to stand music played on some decks due to wow speed variations. Voice only recordings were frequently not so bad to listen to, even if they had the same deficiency. Battery driven portable were often especially bad. On better decks the variations may not be noticeable unless you listen carefully for then or can make measurements. It is often most easily noticed on sustained notes, such as those featured in some piano compositions.

TTs can have the same problem. Your cassettes may have significant wow and/or flutter built in (to the recordings on them). Your deck can't correct this but it can add it its own variations. Apparently digital technology has caught up with the problem. Purely as a curiosity, you might want to look at http://www.audiomastersforum.net/amforum/i...pic,8304.0.html
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dc2bluelight
post Jul 29 2011, 13:16
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QUOTE (AndyH-ha @ Jul 28 2011, 23:44) *
TTs can have the same problem. Your cassettes may have significant wow and/or flutter built in (to the recordings on them). Your deck can't correct this but it can add it its own variations. Apparently digital technology has caught up with the problem. Purely as a curiosity, you might want to look at http://www.audiomastersforum.net/amforum/i...pic,8304.0.html

Yes, cassette machines were bad this way, and if the originals have wow or flutter recorded on them, then the links above are your only way out. Of course, with $150 - $300 budgeted for the cassette deck, it's unlikely you'll have 3,790 to undo flutter!

Based on the budget, I'm guessing this is a non-paid or personal project. Get the best deck you can, and live with it, it's unlikely the deck that recorded the tapes was better than what you'll be buying.
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jaybeee
post Jul 29 2011, 16:33
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QUOTE (vosnos @ Jul 24 2011, 19:52) *
I know there have been multiple topics regarding this subject but some of them are a bit over my head


I wrote a very easy to follow guide here: http://wiki.themixingbowl.org/Digitising_cassette_tapes

There of course even better ways (read: more time consuming and money consuming) to digitise cassettes, which will achieve as good as it gets results. I personally found the way I have done them has produced good enough results for me.

The replies in this thread so far are great, so maybe use what you can from their suggestions and experiment a bit first. Once you've done a few tapes you'll get the hang of it and be knowledgeable yourself wink.gif


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dc2bluelight
post Jul 31 2011, 08:20
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QUOTE (jaybeee @ Jul 29 2011, 10:33) *
QUOTE (vosnos @ Jul 24 2011, 19:52) *
I know there have been multiple topics regarding this subject but some of them are a bit over my head


I wrote a very easy to follow guide here: http://wiki.themixingbowl.org/Digitising_cassette_tapes

There of course even better ways (read: more time consuming and money consuming) to digitise cassettes, which will achieve as good as it gets results. I personally found the way I have done them has produced good enough results for me.

The replies in this thread so far are great, so maybe use what you can from their suggestions and experiment a bit first. Once you've done a few tapes you'll get the hang of it and be knowledgeable yourself wink.gif


Read your blog. Nicely done. You might consider adding a bit about the standard noise reduction systems used in cassette recording (Dolby B and C), and what to do about them. This type of encoded NR cannot be handled by the transforms within Audacity, or any other application. They must be handled in the analog domain. The single-ended noise-print style NR systems available in audio software is good, and may reduce noise, but won't undo the compression that Dolby B or C has applied. Un-decoded Dolby NR compression affects apparent dynamic range and sounds restricted and taught.

You also didn't mention head alignment issues (covered above) which is the single adjustment that will improve your transfer the most. Get this right, and most of the other things you do will work well too. Azimuth, in particular, is so critical that if it's wrong, the tape will sound very dull, and if it's right, the high end might just astonish you.

You mention buying higher-end software for more critical projects, but in the software itself won't improve your transfers at all. What will is a higher-end external sound card, something that will do 24 bits with at least a 19 bit noise floor. This makes input level adjustments far less critical, and the application of a normalizer cleaner because there's more to work with. On-board "sound cards" are always too noisy, and though they may produce a 24 bit file, their performance is barely over 16 bits. Ditch the on-board card, get something good, and never look back.
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2tec
post Jul 31 2011, 18:29
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These days, Naks can be had for a song on E-Bay. My advice, spend some cash, get a good Nak, then sell it when you're done. A great deck will make the job much better and far easier.


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Dynamic
post Aug 5 2011, 12:13
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Another thing to try is Tape Restore Live plugin for WinAmp. You can use it to process your captured audio and use the PCM output to record it for further edting or transcoding elsewhere. It attempts to track and correct for a number of things like Azimuth and has a fairly good Dolby NR reverser (not an exact Dolby decoder, but very close). Seems pretty good for very occasional tape captures on a modest deck, but doing a large project, a good dedicated tape deck and careful azimuth adjustment with correct NR settings is probably the way to go.
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dc2bluelight
post Aug 5 2011, 12:46
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The problem with Tape Restore Live's azimuth correction is that its limited to correcting minor Az errors, you have to fix the big ones with physical alignment. Here's why:

Azimuth errors result in two problems: channel timing error (one channel arrives just slightly before the other resulting in a frequency dependent phase error), and high frequency roll off. The timing error is easy to detect and correct digitally, the HF roll off isn't. The roll off characteristic is rather severe, and the amount of inverse EQ that it would take to correct it would also boost HF noise by a huge amount creating another problem. Yes, you can deal with noise with some sort of processing, but you've now got a chain of digital processes going when you could have done it all with a tweak of a set screw.

If you physically align the head then use TRL to handle the small issues, you're going to get a far better result.
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