[sdiy] Autotuning CEM3340/V3340 oscillators

MTG grant at musictechnologiesgroup.com
Thu Sep 21 04:50:15 CEST 2017


I"m surprised speed is your issue with that SPI DAC, for me it's usually 
the number of pins needed.  Are you right at the top of the speed limit 
for the device, including settling time and all that (do they even 
mention that in the data sheets anymore?)?

But through hole is nice for you. I've been looking for a 12-bit I2C DAC 
in through-hole for some time.


On 9/20/2017 5:19 AM, Tom Wiltshire wrote:

> 
> Another problem is the SPI interface. Since I have to send two bytes to program a 12-bit variable into the DAC (so four bytes for the two CVs) there is a limit to how fast the DAC can be updated. You can then reduce that theoretical maximum another chunk to allow for actual calculation time. This is a problem for something like MIDI pitch bend, where the data needs filtering (e.g. more calculation time) and also needs sending out frequently enough no steps are audible. Adding smoothing to the analog CV would be one solution, but if the steps in the Pitch Bend are heavily smoothed by analog filtering, then no rapid changes in Note CV are possible. Unless you change things around and use a separate channel for Pitch Bend CV, with the Bend CV filtered and the Note CV not - but then that’s three DAC channels for one note! Not very efficient!



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