Glitchy Sub-Octave Generator

[trad3mark]

Ok, so today I started work on something ambitious. It's inspired by the bass in this song:

Now I know that the main bass in that is done on a synth, but like I said, it's INSPIRED BY it, not attempting to directly copy it.

So the idea was to start with a really angry glitchy square wave, use some sort of flip-flop setup, and then add an LPF at the end. After breadboarding a Crash Sync, that seemed to be working really very nicely. My block diagram is now looking something a bit like this:


For the most part, things have been going well. Up to the output of the Crash Sync, I'm digging it. I made a few very slight modifications to it, and it's got a sort of FM Synthesis feel to it that I'm really enjoying. However, in trying to get the sub octaves to work, things aren't going my way at all. Ideally, I'd like to have the signal split three ways, so I could have 3 separate octaves (0, -1, -2) with 3 volume controls. Then have those 3 signals combine again to go through a common LPF, to output.

So first off, is this even possible?

I have a sneaky suspicion that this means I may need 2 x 4013 chips, which I actually have, but do i need something between the Crash Sync output and each of the sub octaves to separate out the signal?

[slacker]

To get multiple octave you could use a counter/divider chip like a CD4024 or CD4040, these have multiple outputs each one dividing the previous one by two, so you can get divide by 2,4,8,16 etc. There's examples of doing this here http://www.diystompboxes.com/smfforum/index.php?topic=76695.0 including using separate volume pots for each octave.
You should be able to drive any CMOS chips straight of the output of the Crash sync or directly from the output of the 555.

[trad3mark]

Ah I see. A huge thanks for that! That slacktave is pretty cool, and looking at +1 octave is something which I would love to add.

I should be able to get that ic this week.

[anotherjim]

If there's a PWM effect going on with the crash sync, dividers will destroy it by making a perfect 50% duty cycle output.
See how it goes with one half of a 4013. Maybe you can gate the octave down output with the input so at least one half-cycle has the pulse width of the input?

[trad3mark]

So far, when I adjust the pot for the crash sync, I get a sort of pwm effect. When I take the signal from half the 4013, its not the same, but it still has a clear audible effect. So I am inclined to leave it as is. The thing is, because that effect is before the octaving effect, its almost like a "global" control. Its not affecting the dry signal only, it has a knock on effect to the octaves, and its distinct, so I think it stays!

[Mark Hammer]

"Glitchy" = unstable tracking?

Elaborate on the deeper meanings of that adjective, so we can help better.

Note that there can be brand-to-brand, and I suppose chip-to-chip differences in the effective threshold for triggering the flip-flop.  Part of the instabiloity in tracking comes from the signal falling just below that threshold on an intermittent basis.  That's at least part of the reason why the PAiA Rocktave used a compander chip: 1) keep the level constant so it stays above that threshold more often, and 2) downward-expand quickly when the signal starts to fall below that threshold too much.

[trad3mark]

Ok well to start off, if you take a clean sub octave, its not that. If you take something like the MXR Blue Box that tracks quite well, its not that either. The earlier DigiTech ehammy pedals that had tracking issues, not really that either.

So if you take the crash sync for example, when you let a note ring out, as it gets quieter, there's a kind of crackly sound to it as it breaks up, eventually gating rather abruptly. That's what I'm after. You can hear it at the start of that Sigur Ros track. The bass sounds quite synthy and what I would interpret as 'glitchy' but perhaps crackly is a better term.

When I use the crash sync, its quite similar to the sound I'm after, albeit an octave or two too high. I also think it could benefit from a trimmer somewhere to limit the gain, but that will be fine tuning later.

Ideally, I'm looking for the crash sync sound, but 1 or 2 octaves down. Bonus if I can split the octaves for that multi-octave sound (I know that's not quite in that Sigur ros song, but I think it would round out the bass nicely).

Does that make sense?

[anotherjim]

Can you drop it octave/s before the "crash sync"?

[trad3mark]

Not really. There's a 'frequency' control on the 555 that gives the crackle effect. I'd need one for each octave, and I'm avoiding that if I can.

[nocentelli]

The 40133 will do a decent dirty one and twovoctaves below, check out the robot devil.