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Old 12 October 2016, 21:15   #42
pandy71
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Join Date: Jun 2010
Location: PL
Posts: 1,546
Quote:
Originally Posted by meynaf View Post
The AY trick is same as 14bit on Paula - combine channels to get more output levels.
Nope it is not the same as Paula using Nyquist-Shanon and PCM and AY is non-PCM so there is tricky apporach for searching particular combination that corespond to linear sample value, SID is even more funny as they use internal triangle waveform to create 12 bit samples (of course they can use attenuator to form crude DAC)

Quote:
Originally Posted by meynaf View Post
I do not know what is the source of nonlinearities from the electric perspective, but you can probably explain this, huh ?
There is plenty of sources, power supply quality is one of factors as it is used indirectly (to power Vref) or directly (as Vref itself).
But if you are really interested there is lot of papers explaining common non-linearity problems in DAC - i will recommend for example http://www.analog.com/library/analog...erters%20F.pdf to see how various non-linearity can be visible in typical DAC .
But generally 8 bit DAC is not simple stacked 8 1 bit DAC's - if this was so simple then decent 16 - 20 bit monolithic DAC will be not so costly - DAC like PCM63 cost around 50 - 80$ depends on grade... (and it consist two 19 bit DAC connected).

Quote:
Originally Posted by meynaf View Post
Of course calibration assumes less bits than available in theory. But in theory we have 16 bits available !
Nope both partially overlapping so there is maybe 65535 but only 16383 are usable and after calibration there is even less.




Quote:
Originally Posted by meynaf View Post
The steps to build the table are quite complicated and i can't tell how exactly it's done.
Thx for code, i was really interested to see what kind of technique is used for calibration - i have source for calibration software but it cover various system aspects and i'm not a developer



Quote:
Originally Posted by meynaf View Post
This has been explained many times, sorry if you don't get it.
I disagree but OK - it is very important for me to tell you that i was curious and it was not personal and i respect you very much and i'm not arguing with your coder skills.


Quote:
Originally Posted by meynaf View Post
There are 65536 possible output levels, of which many are not useful. At the end we get something like 16384, maybe even a little more.
What is so hard to understand here ???
Nothing but more or less we are closer to one of my first statement - IMHO 14 bit Paula will be after calibration close to 10 - 12 bit depends on calibration accuracy, DAC accuracy and power supply quality.

Quote:
Originally Posted by meynaf View Post
Oddly, i've found the exact opposite.
I connected an Amiga to a very powerful amp where the smallest fly's fart would have blown the loudspeakers away. I just got beautiful silence (try this with an Atari ST and you'll understand what noise really means !).
If your Amiga has noise then it's because you removed the shielding and/or added noisy components. Else an Amiga has much less electronic noise than the average PC.
Which Amiga (mostly motherboard revision).
In modern PC analog audio power section design is usually very well designed (separate analog ground plane, linear regulator, way better Vref etc)

Quote:
Originally Posted by meynaf View Post
So yes, that "real audio system"'s D/A are perhaps 16bit, but it doesn't mean it provides better audio experience.
Well trust me - most of them, even cheap players from China can provide 92 - 98dB SNR.


Quote:
Originally Posted by meynaf View Post
Yes, this is the point.
I understand where is difference between us - you see this purelly from arithmetic perspective and for you this is just code that operate in deterministic way and always provide same result for same data - from my perspective electric current is not so simple. Please understand difference between DAC resolution and DAC accuracy - this is completely different - very frequently there is specified something like ENOB https://en.wikipedia.org/wiki/Effective_number_of_bits - it is not uncommon to find for example 10 bit ADC that offer ENOB like 6.4 bit and there is nothing wrong - this is nature of electronics.
http://www.analog.com/media/en/train...als/MT-003.pdf


Quote:
Originally Posted by meynaf View Post
Exactly how many useful values we get out of 65536 is something i don't know. I doubt it's just 4096 though.
It may look very bad but real 12 bit is IMHO very good result.
Attached Files
File Type: c Calibrate.c (25.8 KB, 21 views)
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