Thermistors or NTC's can be used to temperature compensate VCO's. These are cheap, available at 1% tolerance from Digikey. I sandwiched one of these
between the two transistors of the exponential converter using epoxy.
https://www.digikey.com/product-detail/en/vishay-bc-components/NTCS0805E3472FMT/BC2576CT-ND/2237413
A tutorial on exponential convertors and temperature compensation at http://www.schmitzbits.de/expo_tutorial/ shows how.
Most NTC manufacturers have application notes describing how to linearize their response. I used this technique in a VCO I designed about 20 years ago.
It worked very well.
Thank you, i have to read about this, making these thermistors linear for VCO, if i cant find out i will make a topic about this, thanks.
At only 2 channels per DSPIC, with a very fast DAC, you have enough processing power to replicate an analog synth to the point where it would be indistinguishable from an analog synth. You should be able to do 4 to 8 channels with a cheap CD audio grade DAC.
I am using DSPIC33FJ128GP802 with build in stereo DAC ( delta sigma ).
And yes i get 4 voices out of it ( @ 44K1Hz ) with the free compiler, when upgrading compiler i should be able to get 8 voices polyphony.
( i,m to much still a beginner to have external DAC )
What 16 bit audio DAC do you recommend to buy, i dont wanto harvest it out of old CD players.
Once i get busy with 32 bit i need external audio DAC, since there are currently still no 32bit PICs with audio DAC.
Yep, at some point the 'analog' part can be simulated so well you can't tell the difference. It's just a case of processing power. 192kHz simulation is probably enough for sound.
If a analog noise-generator is used for random values in the chip, yes, then you can fool me with digital, else it sounds predictable.
Why do you need one per key? You just need a bank of them and one other master uC reading the keyboard and telling them what to do.
Exact, dont need 128 chips, only the max nr voices you wanto play together.
The only problem i see is how to implement the LFO ?, do you use the ADC on all chips to sample the LFO ?
Floating point DSPs have been reasonably cheap since the early 1990s.
Ok, the 32bit PICs seem to also have fast float supported.
I use this DSPIC wich has very slow float, impossible to use for realtime performance.
I made everything integer, it is more accurate then using float.
When using other chips with float support i can imagine it is still better to use integer math, if you have enough size for all lookuptables.