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Old 13 October 2016, 17:59   #52
pandy71
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Join Date: Jun 2010
Location: PL
Posts: 1,546
Quote:
Originally Posted by meynaf View Post
The situation isn't the same. You forget that these 2x 8 bit DAC have 6-bit volume control.
Exactly however you insisted to use AY nonuniform log scale DAC as comparable to Amiga and due internal AY design those DAC can be stacked (added) when Amiga you can introduce only fixed attenuation to lower part.

Quote:
Originally Posted by meynaf View Post
Yes, checking code words.
What do you think the calibration program is doing ?
Definitely not checking all codes as to do this you must provide stimulus signal that use all possible code values... all calibration doing is checking two overlapping bits (IMHO).

Quote:
Originally Posted by meynaf View Post
Again, you seem to forget that one of the DAC has its output shifted 6 times.
Even if there are only 150 useful sample values - which i seriously doubt - the first sample (8 bit) would have 150, the other (6 bit) 150/4, and that would lead us to 150*(150/4) =5625 values at the end (which is a minimum, for 200 it goes up to 10000), that's many more than your 1500-5000 claim here.
It is 150 useful for full scale but nominally rarely sample values can utilize full scale so finally it is always less... and my claim covers all possible problems in analog path.

Quote:
Originally Posted by meynaf View Post
Btw. If we reduce to 14 bits before calibrating, it implies that non-calibrated 14bit has more unique output levels than calibrated...
It may have non-unique output levels but it doesn't be good (as without calibration overall error can be larger) - once again you extending analogies from arithmetic in ALU to DAC which is not justified.

Quote:
Originally Posted by meynaf View Post
They do not overlap. Same bits don't represent same signal level. If they did, they would be called linear.
So there is no lower 8 bit but only 6 - you have 2 overlapping bits - attenuator introduce 6 bit attenuation so in analog voltage scale you shifting 8 bit low by 6 bits.

Quote:
Originally Posted by meynaf View Post
This has nothing to do here. Other ppl confirmed here that the noise level of our amigas is low.
Glad that everyone can express his opinion about perceived Amiga noise level.

Quote:
Originally Posted by meynaf View Post
You see a confirmation where there is none. Components on the miggy don't make that much noise.
Same as above - i respect your opinion.

Quote:
Originally Posted by meynaf View Post
Yes, isolated. You're speaking about the DAC, the DAC, and the DAC, totally forgetting that it's not the DAC that produce the 14 bit effect.
Nope - i'm trying to cover whole analog path but you insist to speak about arithmetic operations on signal.

Quote:
Originally Posted by meynaf View Post
Repeat as many times as you want, it won't change the fact that what you say here is true only if these DAC are linear, which they are not.
Well so if they are nonlinear and you correcting 2 bits how the heck suddenly 14 bit accuracy was born?

Quote:
Originally Posted by meynaf View Post
But you're not just saying we can't go above 14 bit. You're saying we can't even reach that. Then a 16-bit DAC fed with 14-bit data (2 low bits cleared) would give significantly better results than pseudo 14-bit on the amiga. Experience shows that it does not.
What kind of experience - any objective source of this claim?


Quote:
Originally Posted by meynaf View Post
If there were so much value overlapping, the calibrated output routine wouldn't be able to use many possible values in the 65536 possible ones. How many do you think it uses ?
I don't know and that's why i ask and i strongly consider to measure this (but waiting for Vampire 500).

Quote:
Originally Posted by meynaf View Post
Then define what you call accuracy. As resolution is easy to check but nothing is perfectly accurate.
We not talking about perfection only about objectively quantified parameters that precisely describe DAC conversion capabilities.

Quote:
Originally Posted by meynaf View Post
The lowest output levels required to do 14bit aren't generated by Paula.
Internal resistors, as you call them, don't need more than 8 bit quality. Paula outputs 8 bit, and doesn't need to output anything else.
Well, you can't expect 14 bit accuracy from a component that provide 8 bit accuracy (but due volume regulation design in Amiga with perfect 8 bit DAC it may work as Amiga for volume regulation use PWM and as such it is free from requantization issues - you can have 8 bit with AUDxVOL=1).

Quote:
Originally Posted by meynaf View Post
And this is exactly the reason why more than 16384 output values can be obtained.
Ok, tell me how - we have 16 bit sample, we split them on two equal 8 bit parts, upper part is feed to first DAC directly, lower 8 bit part is feed to second DAC,second DAC has enabled attenuation of 36dB (6 bits), both DAC outputs are combined in analog domain.

Quote:
Originally Posted by meynaf View Post
This implies that a 16-bit DAC would play 8-bit samples (that have been zero-extended to 16 bits) with better quality than a 8-bit DAC.
Yes, with higher accuracy - if 16 bit DAC has better performance then analogue signal will be more accurate (same rule as using for calculation extended precision and later using only most significant bits).

Quote:
Originally Posted by meynaf View Post
Accurary is never perfect, it is always within a tolerance level.
Where one expects 1V output, it may be 1.00033V or 0.99995V.
If you have 44100Hz samples it will never be exactly that, for the simple reason no clock is perfect.
So "14 bit accuracy" is meaningless, or you have to define it.
Well, once again asking you to not use word perfection - it works as 'reductio ad absurdum' as perfection is indefinite .
Please don't involve clock as this lead us nowhere. It will only start discussion about jitter and all related time domain problems related to signal conversion.

14 bit accuracy is not meaningless and can be easily defined - simplest approach is SNR [dB]= 6.02N + 1.76 (where N is number of bits but this is very simplistic).
More accurate are accuracy (quality) descriptions like this http://www.analog.com/media/en/train...als/MT-003.pdf

Quote:
Originally Posted by meynaf View Post
You may pretend accuracy is below 14bit - i can't prove you wrong. Doing so would require precise measurements and i can't do that - i guess you can't either. Perhaps someone else should, settling the matter once and for all ('coz it's starting to be a bit long, in case you haven't noticed).
It is not pretending but curiosity and doubt which is foundation for every person having rational approach to problem.
I have very precision audio analyzer side to me https://www.ap.com/analyzers-accessories/apx555/ - all i need is Amiga with proper signals (as APx555 internal generator can't be used) - to have a proper signals i need to spend some time to prepare those signals (re-sampling to native Amiga sample rate) and need to have Amiga capable to play it (that's why i waiting for V500).
However ANY modern PC card can be used as audio analyzer as usually they parameters are way higher than Amiga audio system capabilities.

Quote:
Originally Posted by meynaf View Post
But if you pretend resolution drops below 14bit - it can be proven right or wrong. And you seem to do so, because you said "only 16383 are usable and after calibration there is even less".
I have this intention especially after such hot dispute.

This may help all of us in more formalized discussion in future:
http://www2.electron.frba.utn.edu.ar...easurement.pdf
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