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Zibri
Account closed
Registered: May 2020
Posts: 304 |
New life for your underloved datassette unit :D
The first phase of testing just ended.
(Still in the packaging and refining phase)
But I wish to share with you all my latest accomplishment.
You might want to check this out:
https://twitter.com/zibri/status/1450979434916417540
and this:
https://twitter.com/zibri/status/1450979005117644800
The fastest example (11 kilobit/sec) has the same (or better) error rlsilience as "turbo250" but it is 3 times faster.
The slowest one (8 kilobit/sec) has the same error resilience as the standard commodore slow "save", but it is 100 times faster and twice as fast as turbo250.
;)
Notes:
1) faster speeds are possible if the tape is written with a professional equipment or hi-fi with a stabilized speed and virtually no wobbling.
2) if the tape is emulated (tapuino or similar projects) the speed can go up to 34 kilobit/sec.
3) even with datassette, higher speeds are possible but the highly depend on the status of the tape, the datassette speed and azimuth. |
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Krill
Registered: Apr 2002
Posts: 2871 |
Quoting Neo-RioWe determined that my deck is probably recording and loading from tape at completely different speeds. Would the pilot signal prior to the turbo file be sufficient to adjust expected pulse widths accordingly? |
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Neo-Rio
Account closed
Registered: Jan 2004
Posts: 63 |
Quote: Quoting Neo-RioWe determined that my deck is probably recording and loading from tape at completely different speeds. Would the pilot signal prior to the turbo file be sufficient to adjust expected pulse widths accordingly?
In an emulator and on the ultimate ii, the pilot signal bars DID NOT MOVE, which shows that everything is in alignment.
With my clone deck after mastering and loading from the same deck those bars had significant jitter... either moving down screen or upscreen, even not that fast but there was distinct movement which highlights the problem I was having.
Also note that I was using a type I TDK C90, so already you have the C2N motor straining to pull a huge reel of tape, and the motor on my clone deck is fairly weak. It sometimes gets jammed trying to spool the tape after FOUND message and the motor restarts - requiring "percussive maintenance" :D
It really is a crappy deck - and yet I still manage to get good TAP dumps of originals that PASS from it - even if it's never normally used to master a tape (and clearly shouldn't given these turbos). I've discovered that Gyrospeed is the best balanced tape turbo for speed AND reliability, given the wide variance of tape decks in various states and conditions. There are faster turbos out there, but all of them require tight speed/motor/head alignment, and headclean of the deck, as well as a good quality tape. Gyrospeed has been a "good enough" compromise.
I've been wanting a new C2N in good condition for a while for my GB64 tape dumping activities, but many go for ludicrous prices now. |
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Krill
Registered: Apr 2002
Posts: 2871 |
Quoting Neo-RioIn an emulator and on the ultimate ii, the pilot signal bars DID NOT MOVE, which shows that everything is in alignment.
With my clone deck after mastering and loading from the same deck those bars had significant jitter... either moving down screen or upscreen, even not that fast but there was distinct movement which highlights the problem I was having. The moving bars don't indicate a problem per se.
They move because the pulse width is slightly off (different motor speed for reading vs writing on possibly different devices), and then that certain integer multiple of it doesn't coincide with a video frame duration any more.
As long as the width is stable (within certain error bounds), all should be good. =)
Now, i'm not so sure about the linearity or lack thereof for different pulse widths.
If the read pilot signal frequency is off the "perfect" (written) frequency by a fixed ratio, does the same ratio apply to all used pulse widths?
And how do preceding pulse widths influence the current one?
Surely the band-pass filter would mess a bit with the signal.
I wonder whether a pilot "training sequence" should use different combinations of all used pulse widths to determine feasible thresholds. |
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tlr
Registered: Sep 2003
Posts: 1737 |
Quoting KrillIf the read pilot signal frequency is off the "perfect" (written) frequency by a fixed ratio, does the same ratio apply to all used pulse widths?
And how do preceding pulse widths influence the current one?
Surely the band-pass filter would mess a bit with the signal.
I wonder whether a pilot "training sequence" should use different combinations of all used pulse widths to determine feasible thresholds.
You are going to have different factors here.
1: there are speed related parameters:
- average speed
- wow and flutter
Wow and flutter are more or less jitter of the speed, but within different frequency ranges, wow being relatively slow.
2: frequency related parameters:
- hi-frequency dampening due to the incorrect azimuth. Recording and writing on the same deck will somewhat mask this though.
- intersymbol interference due to the magnetic media itself, i.e pulses shift around slightly depending how close they are to each other.
EDIT: and effects from the filter in the datasette as well.
Speed related parameters could probably be measured by just inserting a tape with a 1 kHz test tone and crafting a program to extract that information.
The frequency related parameters are more tricky, but a relative measurement could be made by having a program write a test pattern, sampling the data back to ram for offline analysis.
Maybe soci has done some of this already to tweak his pre-compensation scheme? |
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soci
Registered: Sep 2003
Posts: 474 |
You make me release all the crap I have in my drawers ;)
The pulse length calibration pattern for setting thresholds was explored already:
Datassette 4PW Mastering Demo |
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soci
Registered: Sep 2003
Posts: 474 |
Any tape experiments on my side need to wait for at least another month at the moment ;( |
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SLC
Registered: Jan 2002
Posts: 52 |
Quote: Any tape experiments on my side need to wait for at least another month at the moment ;(
Ohnoes! No you're going to upset him by posting your own projects in his thread! ;) Exactly how old is this anyway? |
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soci
Registered: Sep 2003
Posts: 474 |
Started around end of June 2018 then abandoned in August 2018, so more than 3 years.
Anyway I'll stay quiet as suggested. Sorry for spamming this thread. |
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Zibri
Account closed
Registered: May 2020
Posts: 304 |
UPDATE:
the glitching was unrelated to the turbo.. but on a bad init of giana sisters game.
With his "troubled" datassette clone we successfully tested anonfirmed the results I had earlier..
He could write and read back at 8239.33 bit/sec !!!
Now he is testing speed "8" at 9152.42 bit/sec but i guess his limit will be lower... 8239 for his datassette should be the safe limit. |
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Zibri
Account closed
Registered: May 2020
Posts: 304 |
Quote: Started around end of June 2018 then abandoned in August 2018, so more than 3 years.
Anyway I'll stay quiet as suggested. Sorry for spamming this thread.
That's not spam at all...
As I said.. I have never checked or seen any other tape code.
I didn't want to be influenced...
So I started from scratch.
As of now I have a working loader that gives the results I posted earlier (the big table) |
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