[Sam-users] So what's up in SAM Wolrd?

Edwin blink edwin.blink at ziggo.nl
Thu Sep 2 21:06:01 CEST 2021

Hi Stefan


Thanks for explaining. I think I understand now. The higher octave channel must be changed before a full period has passed. A full period @ 61Hz(8MHz / 2^17 ) is ~16.4 ms.

doing a delay of 192 scanlines is ~12.31ms which is good enough. This delay method was probably chosen as it is a convenient way to generate the required delay.


> I do not think that I'm hearing a ticking distortion in SimCoupe (I'm using v1.2.3 dated 2021-08-15


Ah! that explains it. I was using the 1-1-alpha release from Simcoupe website. I should have know to grab the latest version from GitHub:)


Thanks for the help Stefan.


Van: Stefan Drissen [mailto:stefan.drissen at gmail.com] 
Verzonden: donderdag 2 september 2021 19:06
Aan: Edwin blink; sam-users at nvg.ntnu.no
Onderwerp: Re: [Sam-users] So what's up in SAM Wolrd?



Hi Edwin (moving back on list) :-)


Regarding Anton's 4 bit SAA1099 sample player:


You stated: "Snap niet helemaal waarom 192 scanlines gewacht wordt want dit is ongeveer 12,3 ms (192/312*20ms/frame) (een halve periode @ 61Hz is ongeveer 8,2 ms. Maar er zal vast een reden voor zijn en de sample in Rick Dangerous klinkt geweldig!" (you all know how google translate works)


Just jotting some numbers down to see if I can reason why this works:


Tone 0, octave 0 is 31 Hz.

To counter phase this, you need to jump in at 62 Hz.

Frame is 50 Hz


All channels are triggered on line 0 (detected by lightpen port)

Counter phase channels are triggered on line 192 (detected by lightpen port).


Total screen lines (1 frame) = 312.

192 / 312 = 61% 


So I must be missing something - since you are also suggesting something else, 

Unless the lightpen port would return 0 on the first border line, which it does not.


Anton did open an issue on SimCoupe about some very minute differences, see https://github.com/simonowen/simcoupe/issues/36 - but that was about gradual phase shift that became increasingly noticeable.


I do not think that I'm hearing a ticking distortion in SimCoupe (I'm using v1.2.3 dated 2021-08-15) - but well, a SAM playing samples and no distortion? ;-)








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