[sdiy] lookup table as expo converter

[ASSI]

On Monday 24 May 2004 20:24, Paul Schreiber wrote:
> MOTM-520 Cloud VCO does use a look-up table for the expo converter
> (16-bit, 64K entries!)

This seems wasteful unless you do something else (like nonlinearity 
correction) with that lookup table at the same time.  You can split the 
linear code, convert the MS part with a first DAC and feed the 
resulting CV into the multiplying input of another DAC handling the LS 
part. Further compression of the table can be achieved by interpolation 
via d/dx 2^x = 2^x ln2. Some constants can be folded into the reference 
of the multiplying DAC to further simplify the lookup. Since 2^x is a 
simple n:1 decoding function, you may never need an actual lookup table 
or at least not a very large one.


Achim.
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