Digitalizing cassette tapes

I have a Nak MR-2 Deck.....I wonder how I would adjust the azimuth on that deck (if needed?) when I start digitizing some of my tapes and prerecorded ones?

I also have the Sanyo RD5300 deck also which sounds great as well...I suppose I could use either deck. Most of the tapes I have were recorded in Dolby B, a few in C. I still have an old Sony deck that does Dolby S.

I guess that whatever mode the tape was recorded in, should be used to playback when digitizing.

 

Once you have transferred the original 100% analog cassette recording to digital form, why should it matter what NR you use when you transfer (i.e. re-record) the "digital" recording back to cassette tape?

 

Well, look at the reason NR was used when recording the tape. Dolby, and other encoding sliding and/or fixed compander systems are there to reduce tape hiss, which increases dynamic range.

Dolby B, for example, cuts the noise by up to about 10db on a nominal scale. So, when you use the NR to record, the recorder is in effect, compressing half the signal. But, when you play back the tape, all things being equal, you should use the complimentary to get the same sound back that you put in with less hiss because when the treble is complimentary reduced on playback, it pushes the hiss down with the treble boost.

The "decompressed" sound is what you record to digital. OK, I know you already got all that! But, after you digitize the sound, it doesn't matter how you re-record the sound to tape again, if that's what you desire.

If you copy from tape to tape, some people believe that you should not use Dolby. This only works if the deck recording the tape is calibrated the exact way as the playback tape, and the tape types are the same. It also matters if the tapes are running at the same exact speed. In fact, dubbing decks copy without the NR, assuming the decks were calibrated correctly, and, for most decks, that's asking a lot!

BTW, for those who wonder how Dolby works, here's a pdf file: http://www.dolby.com/assets/pdf/tech_library/212_Dolby_B,_C_and_S_Noise_Reduction_Systems.pdf

 

Be careful whilst adjusting your Heads with an ordinary screwdriver you may accidentally touch another part and could partially erase or cause a dropout due to magnetic energy. Find a small plastic and or coated screwdriver. Been there, done that!

 

This was exactly what I meant. At re-recording, it really does not matter what NR I use. I may well use dBX, which can do a better job than Dolby S (up to 100db NR).

 

Noise reduction & other optimizations - USE ORIGINAL SETTING

coopmv, it seems like you are just not getting it... so:

There are four noise reduction systems used on cassette decks. These all are encoding/decoding systems, in that you will need to choose the same type of decoding as was originally used when the tape was recorded.

To overcome the relatively high noise on consumer tape formats, all of the systems use two techniques to different degrees: compression (and expansion on decode), and sliding-band high frequency boost (sometimes variable) that is reduced on playback.

• Dolby B:
  Used in almost all commercially pre-recorded tapes. Up to +10dB boost of high frequencies, and -10dB reduction in noise. Sounds brighter when played back undecoded.
  
• Dolby C:
  Uses two seperate sliding band high frequency boosts, and other techniques to avoid saturation and improve high frequency response. Up to +20dB boost of mid & high frequencies, and -20dB reduction in noise. Sounds quite bright and compressed when played back undecoded. Really needs Dolby C playback .
  
• Dolby S:
  similar to Dolby C, except with more high tech. Sounds more acceptable than Dolby C when played back using only Dolby B, so some late hi-fi cassete releases used Dolby S instead of Dolby B.
  
• DBX:
  Came and went in the mid-late 80's. Uses extreme compression that makes tapes almost unlistenable without correct decoding. Very sensitive to proper calibration, could exhibit 'pumping' if played back in a differently calibrated deck. Basically doubles noise floor to near cd levels.

If you made the original recording, you might know how this was set (maybe your deck only had dolby b...) Maybe you wrote it on the tape..
For home-recorded tapes, it might take a careful ear to pick the correct setting if you don't know how the tape was recorded. (don't be fooled into disabling Dolby B just because the brighter-sounding tape initially sounds better)

There is another consideration - the type of tape. Type I (normal), Type II (chrome oxide), and Type IV (metal) also require a correct setting during both recording and playback. Playback of type II and IV without the correct setting will give a brighter sound. Good type IV tapes have both higher headroom and better high frequency reproduction.
There is a notch in the top of the tape next to the 'no record' tab that indicates if the tape is type II. There is a second notch near the middle of the tape that indicates if it is type IV. Many later decks without 'chrome' or 'metal' switches detect these notches and automatically set the tape type.

There is one other 'Dolby' to mention - Dolby HX Pro. This is an encode-only scheme that auto-reduces tape bias to prevent tape saturation and improve high frequencies. Tapes sound better when recorded with HX Pro, and nothing needs to be done to decode it.

So, to play your tape back (from a well calibrated source, hopefully you can play it back on the same tape deck you recorded it on unless that deck sucked):
- Set the noise reduction the same
- Set the tape type correctly

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Unfortunately in the analog world, there are other considerations that might have affected the original recording quality on that tape you are trying to re-record (besides the possible mistake of tape-type not being set properly):

Tape deck head alignment: If out-of-alignment from how the original was recorded, the stereo signals will be out-of-phase (this out-of-phase high frequency cancellation is what you first detect when you play back the summed signals in mono). Extreme miscalibration will result in the high frequencies starting to disappear, maybe in one channel first.

To adjust the alignment, usually one opens the tape door, and the door cover can slide up and off. There will be an adjustment screw near the tape head. On auto-reverse tape decks with both 'directions' built into the same head, usually the reverse direction's alignment will suffer even when the head is properly set. Some high-end auto-reverse tape decks actually flip the head 180 degrees when they reverse and may have another stop-screw for the opposite direction's alignment. A few very-high-end Nakamichi decks had an alignment control knob on the deck itself.
I would suggest if you still plan on making recordings on your deck, you do NOT mess with the alignment unless you have the skill, test tapes, and equipment to put it back to the correct calibration.

Tape record level: Certainly almost all recording tape decks have the big 'input level' knob to adjust how loud the recorded signal is. There is another recording level adjustment (usually a trim pot inside the deck), to perfectly record +0dB on the tape when the signal level is +0dB. This is the amplification direct to the tape recording heads (after all processing). Without noise reduction this isn't so important, but with noise reduction, this level is quite important, because the noise reduction requires a properly calibrated signal level when both recording and playing back. Probably was set correct enough at the factory, but different tape formulas may have different responses. I am lucky enough to have a deck with this calibration knob on the front of the deck.

BIAS Level: BIAS is an ultrasonic frequency that is also recorded on the tape (required due to magnetic phenomenon I won't discuss here). It needs to be set correctly, otherwise tapes will either sound muffled or too bright, or will saturate/distort. BIAS is what is being adjusted with the different tape settings. It's related to the 'coercitivity' of the tape, how easily the tape is magnetized. Still there is quality variation between brands of tapes and the bias setting might not have been perfect when recording. I am lucky enough to have a deck with this calibration on the front of the deck.

Playback Level:
Here is a calibration that you might actually tweak with, but it will be near impossible to set back to the original if you don't have calibrated cassettes and a good VU meter on the deck or test equipment. This is the amplification level of the tape heads, before the signal goes into any processing. Usually a pair of little pots that are very hard to adjust on the circuit board of the tape deck.

Finally one problem that seems to affect older recordings - the recording is slowly disappearing off the tape! This may be because of 20 years of stray magnetic fields, electromigration, or the layers of tape bleeding through onto each other on the spools. The first thing to go are the high frequencies. This causes problems not only because you lost some audio, but also because the noise reduction requires a proper playback level calibrated to a standard +0dB. With even the proper noise reduction enabled, you might have even more high-frequency loss, and/or audible pumping or brightening depending on the signal level.

--
To summarize, what can you do to get the best cassette recording into your computer?

• Get a deck that doesn't suck. A non-auto-reverse closed loop dual capstan (this feature holds the tape tight to the head without using the felt pad behind the tape) is best. 3-head, Dolby HX Pro, level calibration,... all would have been nice to have used when you made that original recording, but now are just an indication of a more expensive tape deck.
  
• Get an A/D converter that doesn't suck. Maybe something better than the 'line in' on your computer's motherboard. And record in 24 bit, 96K+ if you have it. Record with the input levels as high as possible without distortion or clipping (although you generally can't adjust the levels of the tape deck's line-out, you might play with the both the 'input level' and the 'master level' when recording to get the lowest noise/highest signal)
  
• Pick the correct tape type if your deck has switches for this.
  
• Pick the correct noise reduction setting used on the original tape.
  

Tweaks (especially for older tapes with missing highs):
[easiest to hardest]

• If the tape is chrome or metal, try playing it back as a 'normal' tape. This might give the tape back enough high frequency that it sounds good with the correct noise reduction (you can cover the tabs on the top with tape if your deck auto-senses the tape type).
  
• If the tape was recorded with Dolby B but sound very muddy and even pumpy when it is enabled, you can disable it to record. In your audio software you can use an FFT filter to roll of the highs so they sound correct. (note: too bad software doesn't have an adjustable Dolby B or C feature in it)
  
• If the tape was recorded with Dolby B but sound very muddy and even pumpy when it is enabled, an alternate method might be to record the tape without noise reduction, and then use your software's noise reduction filter. Sample a silent area of tape (not just the 5 second leader) to build a profile, and apply this filter to the whole recording. Although it won't reproduce the original Dolby NR at all, it may both get rid of hiss and roll off the highs a bit.
  
  For the real tweakers:
• Set the head alignment for the best sound reproduction on this tape. You might even need to set it differently for each side of the tape. Once you have done this you will have probably screwed up your ability to make good pre-calibrated recordings again, and you will be constantly tweaking this on future playback as you will soon realize ALL tapes need some alignment tweaks. You can not only listen to the audio in mono to tune for the best sound, but nowadays even view the waveform in software to see how close the stereo is in phase.
  
• Adjust the playback level pots in the deck. This will completely screw up normal playback as much as messing with the head alignment will completely screw up normal recording, but might recover that one tape for you. Turn up the level a few dB to compensate for the loss of the signal on the tape due to age. This is best done with a test tone tape and a meter, so you can easily see that you turned up both channels exactly +2dB or whatever you needed. You can then use the original noise reduction without the missing high frequencies or 'pumping' sound due to miscalibration
  

Enjoy. Maybe an admin can cut and paste all my typing as a sticky if they want?

 

One thing about DBX is that it leaves NO room for fault. The playback bust match the encoding exactly or you're going to have issues.

 

Good post, Harby, and on the money!

One thing I will add about Dolby S is that it is a descendant of the professional Dolby ER, used on master recordings. It was invented in the 80s and was in wide use by 1986. It was specifically created to compete with digital.

Dolby S was a great benefit to the compact cassette, but it came out too late to matter. The former WEA (Warner/Elektra/Atlantic) company used it on cassettes in the early 90s. Ironically, when Sony bought CBS Records, they stopped using Dolby!

Dolby S, along with HX, on good High Bias or metal tape was about the best as cassettes got, IMO.

 

Oh, and clean your tape deck heads too!

 

I thought it was a descendant of Dolby SR, widely used in movie soundtrack recording in the mid-late-80's.

Also, I believe that Dolby S decks had to also have very stringent tolerances for azimuth--or something to that effect. It was part of the "spec" required by Dolby in order for the manufacturer to be able to incorporate the Dolby-S circuit into the deck in the first place. Anybody know what I am talking about?

 

I'm so tired I wrote that? Yes, I meant SR.

The tolerances for Dolby S are stringent, but is more forgiving than Dolby C, which can sound excellent...provided the playback is accurate.

 

Thanks to everybody for your advice: I am going to check the manual and adjust the azimuth as a first step then clean and demagnetize the heads of the ol' Sansui (it is a deck capable of playing/recording "metal" cassettes)!