[sdiy] Quantizer project.. incoming CV's switching point to change to quantized output CV's ...

mark verbos markverbos at gmail.com
Tue Jul 6 14:57:07 CEST 2021

Nice enough idea Brian, but my research shows that 1.2V/Oct is a myth. Buchla 100 systems have a switch to select between the front panel control and the untrimmed CV input. It is exponential in response, but trimming was moot given that there was no keyboard with an output other than tunable keys. The early 200 series VCOs only have CV ins with attenuators as there was not a piano layout type keyboard until the Music Easel (218). Once there was a keyboard that was trimmed, the scale was 2v/octave. This made sense in a 0-15v CV world, which Buchla lived in until he decided to change that out to 0-10v when he switched to blue knobs. The 259, which came out in the late 70s is still 2v/octave at its keyboard input. In 2003 when the 200e was announced, the 1.2v/octave standard was declared.The 225e doesn’t have any trimming on its CV outputs and the one I have puts out around 1.14v/octave. To the 200e, that doesn’t matter anyway, because there is an internal digital bus for the pitch, which controls digital oscillators. When I have made VCOs to be used in 200e systems, I trimmed them to my 225e, but there is no guarantee that they will track on someone else’s. There is a guarantee that a MIDI to CV converter or a quantizer that is trimmed to 1.2v/octave won’t track with a VCO that is trimmed to a 225e though. Paradoxically, a Buchla 225e cannot be used to make a Buchla 258 play in tune unless you plug the CV into both CV inputs.


> On Jul 5, 2021, at 8:41 PM, Brian Willoughby <brianw at audiobanshee.com> wrote:
> Question: Does it even make sense to attempt note pitch quantization on a standard other than 1V/octave or 1.2V/octave? I expect that it would be too difficult with anything else to figure out how to quantize on a logarithmic output.
> The nice thing about 1V/octave is that most DAC chips are very precise with regard to voltage. Some DAC chips even use a 4.096 V reference (or similar binary compatible number) so that each step is precisely 0.001 V. Unfortunately, dividing by 12 gives an irrational number, which is why Buchla uses 1.2V/octave. With 1.2V/octave, a semitone is precisely 0.1 V and a cent is precisely 0.001 V (see those 4.096 V reference DAC chips, and similar). I've also seen DAC chips with a 1.024 V reference.

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