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  #1  
Old 10-24-2013, 01:27 PM
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deromax deromax is offline
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Residual noise on tape

I have noticed on several decks than playing a tape that was bulk degaussed produce less playback hiss than playing the same tape onto which "silence" got recorded over by the deck. It can be heard and measured. In this case, it would seem the record amp and/or erase circuit added some noise onto the tape at record time. If it could be modded/improved, it would seem the potential for overall noise reduction from this mod would be greater than trying to improve the playback circuit. Playback is already better since it's revealing subtle tape noise levels differences. Actually, playback of no tape is even more silent than with a tape.

Just thinking out loud!
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  #2  
Old 10-24-2013, 01:54 PM
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Quote:
Originally Posted by deromax View Post
....Actually, playback of no tape is even more silent than with a tape.

Just thinking out loud!
How do one playback a no tape ???

That aside - it is not uncommon to see the specs mention erasure to be 70dB below 0dB level

but .... virgin tapes has a better signal/noise ratio

Question now - how to avoid the erasure during recording a virgin tape

...... Also thinking out loud + getting a head ache on top of it
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  #3  
Old 10-24-2013, 01:59 PM
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Quote:
Originally Posted by jan_stevns View Post
How do one playback a no tape ???
Simple, hit the play button with no tape You will of course still have noise...but it will be mostly electronic/amplifier noise, not magnetic particles. Even with the best erasure, you'll always have some of that.

Quote:
Question now - how to avoid the erasure during recording a virgin tape
In the cassette section, often people talked about mods that disabled the erase head and used an externally degaussed tape, claiming superior results (lower noise, higher S/N ratios) that way. IMO, this depends a lot on how thorough the degaussing was, how well the field penetrated the tape pack so everything is evenly erased etc.
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Old 10-24-2013, 02:07 PM
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Originally Posted by Velktron View Post
Simple, hit the play button with no tape
That is a no_go on my tapedecks

And honestly - isn't it just another way of watching paint dry ???

Heyyy man - LISTEN to the silence .... errrmmm to what ??


ok - i get it - time to hit the sack here in Scandinavia
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Old 10-24-2013, 02:07 PM
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noisefloor level differences between virgin (unbiased) and biased (recorded) tape are perfectly normal... and these do depend on the tape itself...

any tapes do behave this way...

"unbiased" is when the tape is virgin or bulk erased.

"biased" is when it was used onto a deck, even when recording only silence (or erasing it with a erase head).

usually, when evaluating tapes, it makes sense to measure the "biased" noise as it is just what you will get when using the tape (unless you just enjoy to listen to a blank/unused virgin tape!)

i know this is a R2R topic.... but the phenomenon is the same as it depends on the tape itself and, for cassettes, the true chromdioxide tapes do show a "biased" noise which is very close to the "unbiased" one.

there is also a cassette deck (AIWA XK-S9000) where you can disable the erase head to reduce the bias noise while recording (but if the tape isn't completely virgin then you will "mix" the new recording with the old one, of course)

CHEERS,

Vince.
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  #6  
Old 10-24-2013, 02:52 PM
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Quote:
Originally Posted by vince666 View Post
unless you just enjoy to listen to a blank/unused virgin tape!
You can always claim to be listening to 4'33", and being looking for the perfect execution

Quote:
Originally Posted by jan_stevns View Post
That is a no_go on my tapedecks
How? Even cassette decks with cassette presence sensors can be coaxed to enter into playback mode by holding down the sensors manually -is there a r2r which won't start unless loaded with tape? *scratchin*

Otherwise, you can always try the pause mode -usually the head amp is not disengaged during a pause, unlike a full stop.
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Old 10-24-2013, 08:35 PM
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Yes, playing no tape is trivial : you just bypass whatever end-of-tape device you have, either holding a tape guide in the up position or blocking the light/IR beam to a sensor! Pause or edit mode will do the same.

So just by applying the bias frequency to a tape will raise its noise floor, even if said bias is inaudible by itself?
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  #8  
Old 10-24-2013, 09:16 PM
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Quote:
Originally Posted by deromax View Post
....So just by applying the bias frequency to a tape will raise its noise floor, even if said bias is inaudible by itself?
In my opinion - Yes.
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  #9  
Old 10-25-2013, 12:13 AM
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The erase sections of tape deck is not perfect and it does not randomize the tape oxide layer as well as a bulk erase unit. However, people with no technical knowledge are often coming up with these supposed improvements. Well, they are just not knowing- don't you think the engineers in these companies would have already done that if it were an easy thing to do?
Also, for those that want to disconnect the erase head to their decks- also another stupid idea, get ready for a whole calibration as the load on the Bias oscillator is going to be removed and the Bias will shoot way up maybe much higher than you can deal with. So then you might have to reduce the power supply to the oscillator circuit and thereby modify the deck as well as recalibration if you do this. Most Tape Deck Technicians would say don't mess with that- which is my recommendation as well.
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  #10  
Old 10-25-2013, 07:07 AM
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Quote:
Originally Posted by Skywavebe View Post
don't you think the engineers in these companies would have already done that if it were an easy thing to do?
It's not a question of what the engineers would do, it's about parts and circuit topologies available then and now.

An audio recorder with 110 dB of SNR was impossible in 1960 but is trivial today.

My thread was triggered by the other thread about improving the playback noise performance. I thought that since most of the noise comes from the recording stage, the most benefits would come from addressing that.
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  #11  
Old 10-25-2013, 09:17 AM
speaker dave speaker dave is offline
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And have you noticed that the bulk errased tapes have lower Wow and Flutter too.....
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