Amiga Chinon FB-357A and More Deep Sampling ?

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Gringo
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Amiga Chinon FB-357A and More Deep Sampling ?

Post by Gringo » Sun Sep 28, 2014 10:15 am

There is a Way like the tricks used on Amiga HD Floppy to go More Deeper on sampling, by Lowering the Motor Speed ?
The Chinon FB-357A use this tecnique, to go in HD for limitation of the Floppy Bus....Can this trick used for More HD Sampling on Kryoflux ?
-= Gringo =-
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brightcaster
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Re: Amiga Chinon FB-357A and More Deep Sampling ?

Post by brightcaster » Sun Sep 28, 2014 8:02 pm

Most of all you meed a smaller slice in the head to get more resolution. The old Amiga-dual-speed-drives had a HD-head! So slowing down the rpm doesen't give more resolution from the surface but only to transfer more data by a single rotation.

Regards, David

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Gringo
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Re: Amiga Chinon FB-357A and More Deep Sampling ?

Post by Gringo » Sun Sep 28, 2014 9:14 pm

KF sample at 41.66ns at normal 300rp, if the rotation go at 150rp is like you sample at 21ns, the head have same size but duble the sample ..i think :?:
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mr.vince
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Re: Amiga Chinon FB-357A and More Deep Sampling ?

Post by mr.vince » Mon Sep 29, 2014 9:29 pm

You could also oversample 48KHz source data at 96 or 192KHz... But the source would still be of digital
nature.

At half the speed readout would become very unstable due to several factors, eg head construction etc.

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IFW
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Re: Amiga Chinon FB-357A and More Deep Sampling ?

Post by IFW » Tue Sep 30, 2014 4:24 pm

Drive speed makes no difference for the software (it compensates for it during analysis) as long as the drive itself is still capable working at the speed set. That's why you can read disks perfectly well at various speed with KryoFlux, including speeds not intended, e.g. reading a 300 RPM recorded disk at 360 RPM or vice versa - but any other speed would work just as well.

However, it is worth noting that the filtering/AGC in the drive that amplifies the signal recorded has its sensitivity set according to the expected bitcell sizes, and consequentially according to the drive speed itself.

As an example, if you slow down the drive by a factor of 2 (150 RPM for most drive types) you will end up with 8us, 12us and 16us bitcells for standard MFM DD encoding bands, instead of the expected 4us, 6us and 8us ones.
Most AGCs especially in a HD capable drive might get sensitive at 12us and would certainly fail at 16us - resulting in random flux transitions detected for the slightest change on the track. Ie what you will read be mostly random, over amplified garbage.

If you increase the drive speed, say double it, then you might actually increase the chances of reading something that the drive otherwise is not capable of correctly reading if it is the filtering that prevents the correct sampling. However, you might encounter peak-shift problems for other reasons.

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