DIY Stompboxes => Digital & DSP => Topic started by: David on May 02, 2010, 06:38:53 PM

Title: Sequencing or repeating or whatever you want to call it
Post by: David on May 02, 2010, 06:38:53 PM
Way back when dinosaurs roamed the earth and disco ruled the clubs, I played in a little wedding band.  One of our tunes was "Spanish Eyes".  I would do a guitar solo in the middle that was sixteenth-note double stops.  Our keyboard player had a Hammond X-5 organ.  I seem to recall that he had some kind of function on that thing called a "repeater".  He could do something to that organ to make note(s) repeat as long as he held the key(s) down.  I hated that thing then, but I could sure use that functionality now.

Some years ago, I had aggressively pursued building a MIDI bass pedal controller.  I didn't finish it because 1) I lost interest 2) Our praise band got a good bass player and it was no longer necessary and 3)  I got a bad case of "analysis paralysis" and could never decide on the feature set I wanted the thing to have.  I have resurrected the project and have decided to investigate the possibility of putting a "repeater" function on it.  This is what I would want the thing to do:  I  select the beats per minute the song is being played at.  I then tell the controller that I want it to play half, quarter, eighth or sixteenth notes.  Then, as long as I hold a pedal down, it plays the selected note pattern at the selected tempo until I release the pedal.  This stuff I think I have figured out.  It's just a matter of using the beats per minute and the number of notes per second the controller would have to play to figure out the duration of each note.  That's probably not bad, although I haven't tried it yet.  Note duration is only part of the equation.  Duration of the silence between notes is probably at least as important.

I am at a loss to know how one would determine duration between notes.  I doubt it is as simple as deriving a fixed value you could use for all note values at all tempos.  Could it be, for example, 10 percent of the total time between when one note starts and the next note starts?  For example, at 60 beats a minute, a quarter note lasts a second, or 1000 milliseconds.  If the silence between notes is 10 % of the total time between N1 start and N2 start, that means the actual time the note lasts is 900 milliseconds, with 100 milliseconds of silence before the next note.

Does anyone who is more synth-savvy or MIDI-savvy than I am have any idea how this is done?
Title: Re: Sequencing or repeating or whatever you want to call it
Post by: Quackzed on May 03, 2010, 03:02:25 AM
i believe you could  do it by implementing a tap tempo control on say a choppy tremolo, that is to say, a tremolo effect that doesnt swell to and from loud and quiet, but rather is full volume then cut off then full volume. you'd be able to hear the drummer and tap the tempo in rather than needing a bpm device keeping time ; set up with a led to show you the tempo visually, before you activated it, a momentary dpdt switch to hold when you want the effect and to release when you don't. as far as 1/4 1/8th 1/16th notes ,it would probably be do-able with a 2 pole 6 position rotary switch and different caps or resistors to give some multiple of the tap tempo control signal.
so if you tap in, say 100 bpm, the little light flashes at that tempo. tempo is set. now you turn the rotary knob to 1/16 th note setting which has a resistor that affects the rate of the trem via the tap tempo control signal by some multiple.x2 x4 x8 etc... so if you could use the rotary switch with a multiplier of some kind to multiply the clock signal from the tap tempo, you could just switch it to 1/16th notes and
that would multiply the signal by 4. by 2 for 1/8ths normal quarter notes. even have a setting for triplet 8ths and 16ths.
 8) key search terms  8)  tap tempo    and   multiplier  or clock multiplier.
simple but imperfect, you could build a choppy trem circuit and mod it to have an led that blinks in time. lots of trem circuits can do this already. then just use the knob to dial in 16ths by eye(need a trem that can go this fast), with a true bypass so it always blinks and is always 'on' but you can step on the momentary switch to activate it.

Title: Re: Sequencing or repeating or whatever you want to call it
Post by: JKowalski on May 03, 2010, 09:18:06 AM
The organ "repeater" is a type of tremolo, like quackzed suggested. It uses a kind of pulse shaped waveform so it sounds like the notes get played continuously. It was a common feature on organs, and can also be found as the V809 Vox repeater, a guitar plug-in effect.

But it sounds like you want something quite different, you want a midi playback controller to play predefined notes in a sequence.
Title: Re: Sequencing or repeating or whatever you want to call it
Post by: David on May 03, 2010, 09:55:15 AM
That would make sense.  I rather doubted an X-5 would have had an onboard computer to handle this job.

Yes, what you identified is more what I'm looking for.  What I want is to just spit out a train of notes at the selected pitch (or interval, or chord) as long as I hold the pedal down.  This would not be perfect, but I could construct 8th or 16th note bassline that would be enough for a jam.
Title: Re: Sequencing or repeating or whatever you want to call it
Post by: toneman on May 17, 2010, 01:04:32 PM
how about the slicing portion of a "slicer"?

Or, how bout a "looper".  Sample the exact notes, then Change the tempo out to increase output speed/not pitch.

last, but not least.....
a 555 timer used as the "chopper".
This could be like the "repeater" thingie in that organ.
Depends if U want the "same" notes or want arpegios, or ??
My GR33 can do arpegios: if I hold a chord, it plays the notes one at a time at the adjustable tempo.