DAC "error"

[Chris MacDonald]

> OK, try 8 steps per note:

> 256 * 10.4125mv = 3.361V now you have something to work from!

> But 10.4mv is too big an error, as I suggest you need say 1mv for agrument's sake.

Do you mean that 10.4mV is the resolution error?  The differential
linearity error would be some fraction of that depending on the DAC.

Assuming you mean 10.4mV as a resolution error, I believe this spec is
important if one is trying to accurately hit *any arbitrary* voltage
accurately, not if one is *only* interested in hitting multiples of
83.3mV accurately, starting at 0V (as with simple MIDI/CV converters).

However I agree that even with this "step voltage selection" method a
1/4 LSB 8 bit converter would not have sufficient differential linearity
to meet your pitch accuracy specification.

> The lesson I'm teaching is that you think only in terms of *error*. And that
> has 2 components:
> the "granularity" of the DAC (number of bits) and the lineraity (how
> accurate can you hit a specific voltage
> within 1 step?). 

Yes I understood what you were saying about granularity.  My point was
that if the full-scale output of the DAC is adjusted so that each
discrete step falls on a desired value then the resolution or
granularity of the DAC is not an issue, only the linearity or the
ability to actually hit each step voltage accurately.