[sdiy] trying to understand appregiators in late 70's synths

[Richard Wentk]

On 5 Jan 2009, at 01:10, George Hearn wrote:

> This is roughly how I did it.
>
> 1. Store up to 10 notes held down in a table as incoming note-on  
> messages
> are received.  When a note-off message is received, find the  
> corresponding
> note and make the velocity=0;
> 2. Use a sorting algorithm to sort the notes in order of number  
> ascending
> (up mode) or number descending (down mode).
> 3. Loop through this table outputting the notes if( velocity!=0 )  
> at the
> desired intervals N times where N is the arpeggiator 'range' in  
> octaves,
> each time transposing by N octaves.
> 4. At the end of the cycle, if the mode is 'up+down' use the sorting
> algorithm to reorder the table of held notes. Then repeat the cycle.

The best arpeggiator I've seen is on the Quasimidi Sirius. It does  
this kind of note ordering but morphs it with some preset semi- 
sequenced patterns, some of which vamp chords, while others split  
them. It's very clever and a ton of fun to play with.

CV/gate sequencers aren't very interesting in comparison. Unless you  
have something like a Sequentix P3, which is starting to get smart  
(although a pig to program via a 2-line LCD) most sequencers have no  
musical brain of any sort, so you can't transpose key (not the same  
as transposing the root), or mode, or change inversion, or do any of  
the other things that are trivial with a good arpeggiator.

> The trick I found was to have a good system of remembering held  
> down notes
> in a table and then using a sorting algorithm to order this table.   
> The
> arpeggiator loop itself can then be very simple.

Also, MIDI sync - effectively the arpeggiator has to be running all  
the time, or at least keeping time all of the time, even if notes  
aren't being processed.

Richard