From jerryge at cableone.net Sent Thu, Mar 28th 2024, 21:55
5 octaves * 12 semitones = 60 steps. The 1 volt per octave is a liner input at 0.0833... Volts per semitone (1Volt/12). If you setup your LSB at this voltage an 8 bit DAC can range over 21 octaves (255/12) however that requires over a 21 volt range. Assuming you are thinking of 0-5v for your output and using 4 steps per semitone you can cover 5.3125 octaves using 5.3125 as the Vref. each step would be 25cents or 0.02083... Volts. If you wish to use a 5.00 Volt Vref you will need a higher resolution DAC, for Good results you want to always be +- 3 Cents or less, preferably less than +- 1 Cent. roughly at 5 Volts Vref it runs Bits Steps/Octave S/Semi C/Step 8 255 51 4.25 23.52941176 9 511 102.2 8.516666667 11.74168297 10 1023 204.6 17.05 5.865102639 11 2047 409.4 34.11666667 2.93111871 12 4095 819 68.25 1.465201465 13 8191 1638.2 136.5166667 0.732511293 14 16383 3276.6 273.05 0.366233291 15 32767 6553.4 546.1166667 0.183111057 16 65535 13107 1092.25 0.091554131 17 131071 26214.2 2184.516667 0.045776716 18 262143 52428.6 4369.05 0.022888271 19 524287 104857.4 8738.116667 0.011444114 20 1048575 209715 17476.25 0.005722051 21 2097151 419430.2 34952.51667 0.002861024 22 4194303 838860.6 69905.05 0.001430512 23 8388607 1677721.4 139810.1167 0.000715256 24 16777215 3355443 279620.25 0.000357628 As you can see an 12 bit DAC looks very good at 1.46 Cents per step. And a 16 Bit DAC is well into the overkill range at 9 Hundredths of a Cent per step. - Jerry -----Original Message----- From: xxxxx-xxx-xxxxxxx@xxxxxxx.xxxxxx.xx [mailto:xxxxx-xxx-xxxxxxx@xxxxxxx.xxxxxx.xx]On Behalf Of Stewart Pye Sent: Monday, July 06, 2009 4:57 PM To: Synth DIY Subject: [sdiy] Choosing a DAC Hi, I'm designing an "analogue" sequencer around an AVR micro and I need to choose a DAC for the CV output. It will on only span 5 octaves (0-5V) and output only the equally tempered scale. (there will be a separate circuit for glide). I guess my question really is - how many millivolts can you be off by in a 1V/octave system before it becomes noticeable? Regards, Stewart. _______________________________________________ Synth-diy mailing list xxxxx-xxx@xxxxxxx.xxxxxx.xx http://dropmix.xs4all.nl/mailman/listinfo/synth-diy