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Need help recording from cassette tape.

I have a bunch of old tapes that haven't seen any action in more than 15 years, which I would like to review and digitize and I need some guidance.
As a kid I used tape all the time, but I never had any high end equipment, just cheap stuff... not the cheapest garbage in the market, but certainly never anything fancy in the least. Not a modular hi-fi set up, that's for sure.
As my parents were not into technology, and I didn't have access to much information at all, it's only been recently thanks to the internet, that I've even became aware about the different tape types, for example. Back then, tapes were tapes to me, and that was that.

My plan is to get hold of some reasonably good tape deck, record these things to my computer (nothing fancy) and then try to make the best of it through digital processing on whatever I want to keep.
I need some technical assessment.
I'm pretty sure many of the tapes were recorded with the wrong bias for it's type. When playing them back, should I match the type of the tape no matter what, or is it worth trying other bias hoping to match the one that was wrongly used to record on it?
Also, are modular tape decks like vinyl turntables, needing equalization/de-emphasis?
Finally, should I use an amp or can I record straight from the deck to my computer's line-in?


Re: Need help recording from cassette tape.

Reply #2
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My plan is to get hold of some reasonably good tape deck,
Of course your choices are limited these days.   

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I'm pretty sure many of the tapes were recorded with the wrong bias for it's type. When playing them back, should I match the type of the tape no matter what, or is it worth trying other bias hoping to match the one that was wrongly used to record on it?
I'd choose whatever sounds best.   Then you can use equalization and possibly noise reduction if necessary.   (Audacity has equalization and noise reduction).     But of course, boosting the highs will boost the tape hiss.   And if the tape noise is bad, noise reduction can add artifacts and the cure can be worse than the disease".    Noise reduction works best when you have a constant-tiny background noise...    When you don't really  need it.

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Also, are modular tape decks like vinyl turntables, needing equalization/de-emphasis?
No.   As Roseval says, they have line outputs.    A headphone-output will also work with a line-input and that can be handy when you need a recording-volume control.   (Tapes do have NAB equalization but it's built-into the preamp inside the machine.)

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Finally, should I use an amp or can I record straight from the deck to my computer's line-in?
Line-in on a regular soundcard is fine.    The "tape out" on a stereo system is usually just a direct (switched) connection to whatever is connected, except for the turntable which goes through a preamp.   Most laptops don't have line-in, so if you have a laptop you'll need a USB audio interface with line inputs.     There are also cassette players with USB outputs but most of those are "cheap little gadgets".

Re: Need help recording from cassette tape.

Reply #3
Noise reduction can be tricky for something already recorded to analog. There are good (and perhaps pricey) cassette players with built-in noise reduction more suitable for cassette tapes. I've used Audacity's noise reduction tool before, and I'm not sure I'd recommend it apart from recording directly from microphone.

Re: Need help recording from cassette tape.

Reply #4
@Roseval Thanks for the link, I'll check that out for sure.

@DVDdoug Well, I didn't mean buy a new one. I know well made, full featured ones are not produced anymore. I was talking about getting something second hand and sell it back when done, probably from some pawnshop for convenience, or, with some luck, someone will be kind enough to lend one to me for a little while. I don't plan to hold on to these tapes after I'm done, nor do I intend to start a hi-fi setup.
As for my computer, it's a custom desktop build. Nothing fancy, though, and it's quite old already. It's integrated audio, but not too bad, I think. Does HD audio, not that that I can hear the difference, nor does that say anything about the quality of the analog stage or the DAC. Seems to have just under -96dB RMS noise floor with about -84dB peak when nothing is plugged-in according to the Audacity Monitor, and up to -72dB peak with something plugged, depending on format selection (it seems to perform best the lower the sample rate, does that make sense?). I suppose that will be plenty for tape and vinyl digitization? And there's probably room for improvement with a better shielded cable than what I'm testing with now.

As for the bias selection, I was asking in hopes of avoiding a bit of testing and guesswork, but I suppose there's not much of a shortcut, eh?

@ajp9 I never said anything about noise reduction, but that's surely something I'll be looking into after recording. While I've never done anything serious with it, I did toy arround with noise reduction in the past, mainly with goldwave, and I know how you can easily ruin things if you get greedy :) even with the noise profile method you have to keep your expectations to a reasonable level.
Nevertheless, are you saying that you recommend the noise reduction system that the deck might have over digital attempts?

Re: Need help recording from cassette tape.

Reply #5
... I'm pretty sure many of the tapes were recorded with the wrong bias for it's type. When playing them back, should I match the type of the tape no matter what, or is it worth trying other bias hoping to match the one that was wrongly used to record on it?
Also, are modular tape decks like vinyl turntables, needing equalization/de-emphasis?
Finally, should I use an amp or can I record straight from the deck to my computer's line-in?

I use a Nak BX-300 which allows me to fiddle with the bias, which I do by ear, on a per tape basis. Some Naks also allow for head azimuth adjustment, which can help a lot. I just connect my deck right to the line in on my soundcard with a RCA to mini jack cord, and I use Audacity. I follow the Audacity workflow instructions and the results have been good.

http://www.hifi-classic.net/review/nakamichi-bx-300-414.html
Quis custodiet ipsos custodes?  ;~)

Re: Need help recording from cassette tape.

Reply #6
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There are good (and perhaps pricey) cassette players with built-in noise reduction more suitable for cassette tapes.
I seem to remember something called ANR (automatic noise reduction).   It was rare, not "high end", and I'm pretty sure it was single-ended (applied only to playback).  Modern digital methods should be much better and there are more options for tweaking the software.

The most popular noise reduction was Dolby B.  (Dolby A was for professional reel-to-reel decks.)  Dolby is complementary.   It's applied during recording and "reversed" during playback and I don't recall any negative side effects.   Dolby B isn't to "drastic" so the tapes can be played-back without it, and you get a slight non-linear high-frequency boost.   

Many listeners would listen with Dolby turned-off because they liked the "brighter" sound (high-frequency boost).   Dolby C came along later.  It was better (better signal-to-noise) but I believe that since it was more aggressive, it was less-compatible with players that didn't have Dolby C decoding.   Every deck that had Dolby C also had Dolby B, and if it doesn't say B or C, it's B.

There was also DBX noise reduction, which was 2:1 compression during recording with complementary 1:2 expansion during playback.  This virtually doubled the signal-to-noise ratio but it was totally unlistenable on a deck without a decoder.   It was very rare.

Note that bias is ONLY applied during recording and the optimum amount of bias varies with tape-type.  There may be a "tape type" setting for playback but that's not actually bias.

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As for the bias selection, I was asking in hopes of avoiding a bit of testing and guesswork, but I suppose there's not much of a shortcut, eh?
Its just a switch so it's easy enough to take a quick-listen, and it wouldn't make sense to use the "right" setting if the "wrong" setting sounds better.  ;)     The Dolby setting is a little trickier because it will always sound "brighter" with Dolby turned off.  But still... whatever sounds best...

P.S.
Related to your other post - I've never heard wow or flutter from a non-defective tape player, but you could have defective tapes or tapes that were recorded on a defective recorder..

Re: Need help recording from cassette tape.

Reply #7
I'm sure there's software better than Dolby tape deck noise reduction... it's just not Audacity's built-in effect IMO. :) A good idea to keep the unadjusted file in case you find better.

Re: Need help recording from cassette tape.

Reply #8
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I'm sure there's software better than Dolby tape deck noise reduction...
You're making an "apples to oranges" comparison.   Dolby is a complementary process (recording and playback).   A tape recorded and played back with Dolby has lower noise than a tape without it.  A tape recorded with Dolby should be played back with Dolby, and if you are playing tapes without it should be turned off. 

In either case you can use digital noise reduction and you may, or may not, get artifacts.    Digital noise reduction works better if you start-off with lower noise (such as a tape with Dolby).

Re: Need help recording from cassette tape.

Reply #9
These tapes are mostly homemade recordings or transfers, accumulated over the years, most of them with mysterious contents, and who knows how observant of the proper recording practice. I know when I recorded tapes back in the day it was in kind of cheap decks, with no attention to or concept about tape types and bias and whatever else.
Many of them are probably vinyl or CD transfers, or even second of third generation tape transfers. There are tapes that belonged to me back in the day but also others that I never touched.

Re: Need help recording from cassette tape.

Reply #10
Especially with a motley collection of tapes like that, which is what most people have, just give it a go. Unless you're trying to do some kind of 1:1 as pristine as possible archival copy, the result that sounds the most pleasing to you is going to be the one you're happiest with.

Save an unprocessed lossless archival copy before you start doing any processing. That way you can always go back and redo it.

Re: Need help recording from cassette tape.

Reply #11
So. I'm using a cheapo CD+MP3+tape+radio I found lying arround in the house, and I'm surveying the tapes, mainly by recording them in the background and then quickly listening through it and skipping whatever I'm not interested in.
Even though it's a crappy machine and it has a heavy stereo balance problem (I opened it trying to find some pot to adjust or something, but it's all a mess of cheaply soldered wires flying arround and I'd have to undo too many things to even try to find that, so fuck it, and the unbalance seems to be sorting itself out, oddly enough), I burned a fullscale 1kHz signal on a CDRW to adjust the gain on the device and my soundcard and found where they start clipping. Also used RMAA, just for kicks, both on the CD and a CD to tape transfer on the same machine (you can imagine the poor results of that...). Maybe I could also try a more extreme signal, 2 samples fullrange positive, 2 samples fullrange negative (surely has a name, but I don't know what it is), and see what it does with it xD Somehow I doubt it will do a proper 11025 sine over fullrange.

Anyway. Even though I'm not going to be rely on these adhoc captures for anything I want to keep, the resulting recordings made me think about dynamic range, noise and dither.
Obviously tape won't exceed 16bits, so, at some point, I should reduce the depth, but even after ajusting the gains, most tapes seem to be very low volume, so I think it should be a good idea to do some extra things before.
I'm recording at 24bit, just to make things easier later, and 44100Hz, as the card seems to have higher noise the more I raise the samplerate (though this could well be high frequency noise, now that I think of it... I need to do further testing).
Now. In order to reduce bitdepth to 16bit as safely and as "losslessly" as possible, I understand I would need to apply enough gain until the noisefloor of the signal raises above the 16bit equivalent noise floor, while making sure that I don't clip.
How would I go about this?
Also, would I need to add dither noise or is the abundant noise already available on the signal enough for the job, asuming I properly get that noise floor avobe the 16bit mark (maybe 15)?
As you can see, I kind of get these concepts, but I usually waste a lot of time trying to find how to put them into use with the tools available.

Maybe I'm overthinking all this?

Re: Need help recording from cassette tape.

Reply #12
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I burned a fullscale 1kHz signal on a CDRW to adjust the gain on the device and my soundcard and found where they start clipping. Also used RMAA, just for kicks, both on the CD and a CD to tape transfer on the same machine (you can imagine the poor results of that...). Maybe I could also try a more extreme signal, 2 samples fullrange positive, 2 samples fullrange negative (surely has a name, but I don't know what it is), and see what it does with it xD Somehow I doubt it will do a proper 11025 sine over fullrange.
I don't understand the point of that since the tapes are already recorded and the levels are what they are.   Or, are you adjusting the playback level?   Usually there is no playback volume control on the "tape output" and if there is there is usually enough analog headroom that it won't clip (even if you can clip the speaker-output).   You can use the analog volume control to adjust the digital recording level.

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Now. In order to reduce bitdepth to 16bit as safely and as "losslessly" as possible, I understand I would need to apply enough gain until the noisefloor of the signal raises above the 16bit equivalent noise floor, while making sure that I don't clip.
How would I go about this?
At 16-bts (or more) the quantization noise is insignificant compared to any analog noise.   Just as a reference, pros typically record around -12 to -18dB (at 24-bits).     You don't need to leave that much headroom (pros don't need it either ;) ) but the point is, low levels are OK...   You can boost digitally later.    With analog tape, you needed a hot signal to overcome tape noise, but this is digital so no tape noise!    Also, tape soft-clips as you go over 0dB but digital hard-clips at exactly 0dB.    Digital recording levels are not critical as long as you avoid clipping.   


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Also, would I need to add dither noise or is the abundant noise already available on the signal enough for the job, asuming I properly get that noise floor avobe the 16bit mark (maybe 15)?
The "rule" is to dither whenever downsampling.    But at16-bits or better, you wont hear the dither or the effects of dither under any "normal conditions".   And you're right, records & tapes you already have noise that's higher than the dither noise...  It's "self dithered" and you're not to hear the slight additional dither (or it's effects).   So dither or not, you're not going to hear the difference... 

 

Re: Need help recording from cassette tape.

Reply #13
Getting a reasonably good deck is a good idea, but assuming you don't plan to digitize tapes for years to come, I actually suggest borrowing one from someone that is a tape enthusiast.
I don't personally own one, but I have access to an Aiwa AD-S950 (if I ask nicely). A really nice deck, and the person owning it replaced the belts a couple years ago and generally keeps it in a very good condition.
This is actually something to take into consideration when getting one. Quite often, getting a tape deck from the 80's or 90's means refurbishing it, before using for the first time.

My ADC is a Behringer UCA202. That external USB sound card is not brilliant. It's good enough to digitize tapes and vinyl, and the analog line output is fine, too. The headphone amp inside that thing is atrocious though. When running for a couple hours, it introduces noise, sometimes in the left channel sometimes in the right, mostly in the right. It's not a great general-purpose sound card, but as a small step above the regular line-in of your on-board sound card, it's quite cost effective.
It also as a TOSLINK output, which I never used.

To record, I mostly use SoX, as it's a simple command line program. I usually edit the file (usually recorded to FLAC) with Audacity, later.

You can get both SoX and Audacity for Windows, too.

 
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