Any ideas as to why I'm getting this behaviour would be cool.
So, if I feed a sequence into the volt/octave input that consists of the “C” major scale ie: C D E F G A B C
it will play that back just fine. However if I turn on the VCO’s built in quantiser, set to chromatic, it plays back C sharp D E F G A B C.
I have calibrated the VCO so it’s not that. I’m completely baffled as to why the first C is sharp.
Quantizing already quantized notes leads to a dark portal of mysteries and small voltage offsets.
Add a small +- voltage offset to your input cv and your half step off will be fixed, or migrate.
Depends on how your quantizer rounds up or down when the input is close to a note.
noodlehut.bandcamp.com
Quantizing already quantized notes leads to a dark portal of mysteries and small voltage offsets.
Add a small +- voltage offset to your input cv and your half step off will be fixed, or migrate.
Depends on how your quantizer rounds up or down when the input is close to a note.
The notes from the sequencer are not already quantized. Its a digital sequencer so the voltages are just precise.
So the fact that just the first note is getting shifted up a semi tone really makes little sense to me.
But I don't build or design modules so thats not much of a surprise.
I have repeated the experiment but instead of using the built in quantizer I used an external one and the sequence plays as expected.
So it does appear to point to some issue with the internal quantizer to me.
I got bit by this once too. Your quantizer is working correctly.
It's analog, so what does 'precise' really mean?
You need a voltage to play a C2, so you request that precise 2.000 volts from the digital side.
But there's the D/A and wires and jacks and dusty pots and humidity and transistors drifting from heat.
By the time it arrives at the quantizer's A/D converter, maybe it's 2.01 volts, maybe it's 1.99 volts.
Only a 0.02 volt difference, but the quantizer wants to round them to two different semitones.
This behaviour also depends on your specific quantizer's rules for how it rounds to the nearest note.
It's analog, so precise is always relative and non-linear and squishy.
The non-linear part is important too.
What happens at 1.99 vs. 2.01 volts might be different than the response from 2.99 vs. 3.01 volts.
(only the low C went sharp, but not the higher ones)
Think squishy, not digital.
Dieter said it best:
General function and problems of quantizers
When the input CV of the A-156 changes the module converts the incoming voltage into a stepped voltage at the correspondig CV output. For this there the modules uses voltage thresholds in 1/12V steps. If the incoming CV is very close to a threshold value it may happen that this voltage is converted once to voltage 1 and later to voltage 2 (with voltage 2 = voltage 1 +/- one step or +/- 1/12V). The A-156 does not "know" that the voltage comes from the same source. It just converts an incoming non-stepped voltage into a stepped voltage.
Example: think about a sequence with N steps where the voltage of step #3 is close to a threshold. When the sequence is running it may happen that for step #3 two different voltages appear (+/-1 semitone) at different passes. To avoid this flaw the quantizer would have to "know" that it has to convert a sequence with N steps and that after N conversions the same CV as during the last run has to be generated - provided that the voltage is very close to the former value. He would have to memorize the "old" voltages of all N steps and compare them to the "new" voltages. When the difference between an "old" and "new" voltage is below a certain threshold (e.g. less than half a semitone or less than half of 1/12 V, i.e. about 40mV) the old output value is taken. But this job cannot do the A-156 as it does not "know" anything about a sequence structure but simply converts the incoming continuous voltage into a quantized voltage.
To avoid this the quantizer and the sequencer would require a common "supervisor". For example with our Dark Time stand-alone sequencer this would not happen as the quantizers "knows" the values of all controls during the last run because they are stored in an internal memory. When the advance to a new step is triggered the unit compares the new voltage to the stored voltage of the last run. There has to be a significant difference between the two values. Otherwise the same voltage is generated. Without storing the values of the former run this would be not possible. This problem occurs for all quantizers which are not embedded into the sequencer structure because they don't not "know" anything about a sequence but simply convert the incoming non-stepped voltages into stepped voltages.
Even already quantized control voltages should not be used as CV source for the module. In this case similar problems may occur if the voltage steps of the incoming signal are close to the voltage thresholds of the A-156. In this case it may help to add a small offset voltage to the incoming CV signal so that the voltage steps of the incoming signal are no longer close to the voltage thresholds of the A-156. But the general question is: why using a quantizer if the control voltages are already quantized.
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noodlehut.bandcamp.com
I really appreciate the vast esxplanation on how a quantizer works and I understand the principal. But I really think the point of what I'm saying is being missed. The Oscillator will play the scale perfectly without the internal quantizer being switched on.
So the voltages coming from the sequencer are precise enough to produce the correct pitch. Both the sequencer and the oscillator are digital as well. As I said in my previous post, I have tried putting an external quantizer in the signal path and it has zero impact. All the notes in the scale are played correctly. Only when I turn on the oscillators built in quantizser do I get the problem and its only the first not in the scale that is a semitone sharp. So adding offsets will just put everything else out. I know because I have tried it already. The only explanation I can think of is that that the internal quantizer is in some way faulty or incorrectly programmed.
Can I have your broken oscillator?
-- noodle_hut
Sure you can.
Where do you live? I will pop it round shortly.
