4 Channel 10 Octave Bipolar Quantizer References: Chris List ARP Style Quantizer David J Brown Modular Synthesis This quantizer is intended for a sequencer project. I designed it as a bipolar quantizer so that external bipolar signals could also take advantage of the quantizing function when not in use by the sequencer.
It's based off of the 'ARP' concept of sampling the stairstep voltage produced by a DAC. It works very well, though it contains more parts than I'd like. The hard part for me was producing a decent trigger signal in order to sample the DAC staircase. I ended up using four comparator IC's rather than two duals because the dual packages would bleed enough signal through to 'confuse' the other channel. This configuration is very reliable, and makes tuning a sequencer to standard Western temperament very easy indeed. Running an LFO through it at moderate speeds produces stepped arpeggios. Using it with a sample and hold produces even tempered sequences.
Instead of a ripple counter, I opted for two synchronous four bit counters to reduce glitchiness. Originally, I did use a CD4024 ripple counter and two latches, but I found this arrangment worked just as well, less one 16 pin IC.
Running very slowly changing CV's through it will produce glitches at the comparator 'decision points'. This will result in a bit of chaotic detuning as the voltage passes through this point because the comparator has to decide if it's a 'step down' or a 'step up'. Therefore this design is best used for tuning sequencers, for medium to fast S&H sequences, or for creating tunes out of combined pulse waveforms such as LFO's, etc.
Thanks to David J Brown for posting his Quantizer Lag, and to Chris List, who posted the initial design long ago.
Quantizer Schematic and Theory of Operation (581 kB PDF) Important!! Page 1 of the schematic in the PDF contains two errors:
1. Carry In of the first CD4516 is held high - this prevents the counter from counting. Corrected schematic has it held low.
2. On each 4516, Q3 and Q4 were reversed, causing an irregular count. Corrected schematic has put them in their rightful places.
When I can get the corrected schematic incorporated into the PDF, I'll upload the entire PDF as a correction. Corrected Schematic Page 1 (169 kB) |
