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Old 12 October 2016, 20:01   #40
pandy71
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Join Date: Jun 2010
Location: PL
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Quote:
Originally Posted by NorthWay View Post
Erm... if the volume control scaling is not linear (not using same size steps as the DAC), does that not make it possible to get better than 14 bit result? (Or worse for that matter.)
It is not important as we have 8 bit DAC with level 1 and we not touching 8 bit samples (with exception of calibration as they partially overlapped will address this later as pointed byrobinsonb5).

Quote:
Originally Posted by NorthWay View Post
I.e. smallest sample value (well, isn't it the difference between two values really?) at full volume is louder than the biggest sample value at minimum volume?
Nope - accordingly to HRM for AUDxVOL=1 attenuation is approx -36.1dB so this is maximum dynamics that can be added to (theoretical) 8 bit DAC dynamics.

Quote:
Originally Posted by robinsonb5 View Post
I think the point Meynaf's trying to make is that when two channels are combined to do 14-bit, the channel that's at 1/64 volume is still an eight-bit DAC, and some of its range overlaps the range of the full-volume channel.
Yes, fully agree but it is not a problem - problem is how to select from 65356 sample values corresponding 16383 and with calibration less than 16383 (as this is lack of linearity - some values are not linear and they are lost i.e. for 1024 voltage or current should have particular value x when for 1025 it should be x+(1/16383) but it can be x i.e. missing code i.e. non-linearity)

Quote:
Originally Posted by robinsonb5 View Post
This means we can input 65536 unique codes into the combined DAC, rather than the 16384 that a true 14-bit DAC could accept.
Nope - this means that 2 LSB from upper 8 bit overlapping partially with lower 8.

Quote:
Originally Posted by robinsonb5 View Post
It's highly likely that non-linearities in the DACs mean that the vast majority of those 65536 codes give a unique output level, and with careful calibration (that the current calibration software may well not be doing sufficiently well) it may be possible to achieve higher than 14-bit resolution, but only in very specific (and not very useful!) parts of the range.
Nope as you reducing volume by only -36dB so ranges from upper 8 bit and lower 8 bit are partially overlapping, also both 8 bit DAC suffer from non-linearity and based on fact that they share same die is more likely like they will have very similar characteristic of non-linearity i.e. can't be nullified by simple combining DAC (it could be compensated if you switch DAC's to pseudo-differential configuration - feeding one of DAC's with negated sample values - this will extend they dynamic range by 1 bit so two 8 bit DAC in pseudo-differential configuration will behave like 9 bit DAC) - stacking two very similar non linear DAC will only increase issue so they will be never close to theoretical 16 bits - more realistically they will be rather 12 bit.
Calibration is very important but in fact it will further reduce number of available sample values... this is quite.

Last edited by pandy71; 12 October 2016 at 20:41.
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