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Flavioweb
Registered: Nov 2011
Posts: 447 |
Doubts about Datassette calibration.
I recently came into possession of a speed calibration tape for professional audio plates.
It contains a 3000hz square wave which I used to calibrate the speed of my Datassette.
I have an original copy of Robocop and R-Type which I use as a reference for azimuth calibration.
With the Datassette calibrated in speed using the calibration tape and in azimuth using the two games I cannot load these two originals correctly at the same time.
The games are originally mastered at different speeds (I think due to the datassettes used by the software houses to create the masters). In fact if I adjust the speed of my Datassette to read the CBM standard sync of the tape (TAP value $2F / $30) at the correct speed of 2593hz (pal), the other game is always slightly faster or slower (depending on which of the two I take as a reference).
In itself my datassette, if calibrated in speed with the reference tape at 3000hz and in azimuth with one of the two games, gives the best performance: I can write and reread some of my tapes using higher frequencies.
On the other hand, if I manage to load both games, the performance of the datassette deteriorates (I can reach lower speeds with my tapes).
Hence my question: what references did CBM use for datassette calibration? Is there any document out there that contains information or does anyone have any ideas? |
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chatGPZ
Registered: Dec 2001
Posts: 11129 |
I doubt those devices were "calibrated" in any way. Its just a motor that roughly runs at the right speed :) |
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Ziaxx
Registered: Oct 2020
Posts: 15 |
I don't know if this is useful for you as it's mostly about Turbotape, but pretty interesting nevertheless.
https://www.atarimagazines.com/compute/issue57/turbotape.html |
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Flavioweb
Registered: Nov 2011
Posts: 447 |
Quote: I doubt those devices were "calibrated" in any way. Its just a motor that roughly runs at the right speed :)
This is THE point: which is the "right speed"?
For standard "compact cassette" calibration speed is 4.76cm/s.
But what will CBM have decided?
https://en.wikipedia.org/wiki/Audio_tape_specifications |
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chatGPZ
Registered: Dec 2001
Posts: 11129 |
My guess would be its a standard cheap tape drive, which they bought from a 3rd party just like the floppy drives.
Did you check (not sure how...) those 3 tapes that are involved in your experiment for "stretching". perhaps its just enough to make it no more work for one case? |
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Flavioweb
Registered: Nov 2011
Posts: 447 |
The tapes are short.
At a glance they seem to work correctly.
The magnetic tape runs smoothly and the felt pads are in place.
As I always do before using tapes that I haven't used in a while I did a fast forward and a rewind on both sides.
However, there is a datassette setting that allows you to use both, but this setting is not "theoretically" the best possible.
When everything is calibrated to the state of the art (speed and azimuth) one of the two games stops working and if I adjust the azimuth to make the one that doesn't load work, then the other one stops working.
I would have expected these two originals to work and instead only have problems with other "cheap" cassettes I have.
Obviously this is not the case ... |
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chatGPZ
Registered: Dec 2001
Posts: 11129 |
That sounds odd, you shouldnt have to fiddle with azimuth at all when dealing with originals only. Once it was adjusted correctly that is :)
What i'd try... put those two games aside, use other originals (and more than two) :=) calibrate it, and then load them. If then its still just one of the two that you originally used, then perhaps that tape is somehow degraded? |
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Flavioweb
Registered: Nov 2011
Posts: 447 |
Meanwhile i found this:
https://youtu.be/yhguHf-4zDM |
