[sdiy] Techniques for Multiplying MIDI Clock frequency?

[Spiros Makris]

There are all excellent suggestions!
I happen to have a prototype with a teensy 3.2 and midi In/Out capabilities
on the bench, so I think I'm going to experiment with that first.
The counter method is an open-loop approach, pretty much, and what I'm
going to try first. I suppose if I closed the loop somehow it would become
a "proper" DPLL. Maybe if I build a software phase detector and use the
error signal in combination with the counted value to get more steady
results?
I believe going for the maximum clock speed and resolution combination for
the frequency chosen (clock frequency / counter size < max midi clock
frequency ?) is what will give the most accurate results.

Spiros

On Fri, 17 Dec 2021 at 19:24, The SynthiMuse <synthimuse at gmail.com> wrote:

> The clock multiply technique I used ( just once ) is that I just outputted
> multiple midi clock messages for every incoming clock message.
> I measured the incoming clock period so that when I was sending multiple
> clocks out, I spaced them appropriately between incoming so there was
> minimum jitter in the outgoing stream.
> The max practical speed I was working to was 250bpm. This would equate to
> a clock pulse every 2.5mS.
> I suppose I implemented a coarse DPLL and it worked ok, with the
> limitation on maximum speed.
> I'm afraid the code is long lost or I would happily pass it to you.
> Gerry
>
>
> On Fri, Dec 17, 2021 at 10:50 AM Roman Sowa <modular at go2.pl> wrote:
>
>> Measure incoming clock period with a timer. Then divide that measured
>> timer value by the number you want to multiply the frequency. If you say
>> anything between 10 and 100 is fine, then dividing by 32 sounds like
>> walk in a park. And that divided value (or simply shifted in case of 32)
>> is then loaded as period for another timer that outputs a pulse on
>> overflow.
>> This way after each incoming clock pulse you get immediate response of
>> updated frequency multiplied by 64 (or whatever other value)
>>
>> Roman
>>
>> W dniu 2021-12-17 o 08:03, Spiros Makris via Synth-diy pisze:
>> > Hello List,
>> > I want to experiment with polymetric structures and create "non
>> > standard" subdivisions within the standard ones supported by MIDI. I
>> > have only worked with the 24ppq, using the timing messages to directly
>> > drive the sequencers. I would like a way to multiply the clock
>> frequency
>> > in order to increase resolution, let's say by 10 or maybe 100 times, if
>> > that's feasible (I think it is?).
>> > I think this is achieved by a PLL. I understand the basic concepts of
>> it
>> > and have used in the analog domain, but never did it in a digital only
>> > format. Furthermore, I suppose having an array of hardware peripherals,
>> > such as timers and interrupts, and a fairly fast processor (teensy 3.2)
>> > could open up other approaches that don't follow the standard PLL
>> > configuration.
>> > This has been on my mind for some time, but I don't really know where
>> to
>> > start. Any advice, or resources are greatly appreciated
>> >
>> > Regards,
>> > Spiros
>> >
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