long digital delay build log

[deadastronaut]

hours of fun...

btw are those 9mm pots plugged into the breadboard?..

[cloudscapes]

9mm, yep! keeps wiring  down

http://smallbear-electronics.mybigcommerce.com/alpha-single-gang-9mm-right-angle-pc-mount-w-knurled-plastic-shaft/

[deadastronaut]

cool, ive been using trims on bread for ages, but those are miles better...cheer etienne.  

http://www.taydaelectronics.com/potentiometer-variable-resistors/rotary-potentiometer/linear/1k-ohm-linear-taper-potentiometer-round-knurled-plastic-shaft-pcb-9mm.html

ordering time..

[cloudscapes]

Yep, they're super handy! I usually get a whole bunch of the same value and tweak the value afterwards with parallel resistors. Snap off the metal ears and you're good to go!

I realized I made a mistake. I initially said I had 16bit internal headroom even though my ADC is only 12bit. That would make sense if my feedback path was digital. But it's not, it gets converted to analog then back to digital with every delay. That's what gives it character, but at the same time I don't get the full headroom after all. No biggie.

Currently redoing the opamp stuff much neater tonight, with a whole row of unity gain buffers ready to be patched into. It'll make testing much easier. Also, I need to do some kind of diode limiter for the ADC.

[cloudscapes]

Redid the opamp stuff, neater/better (hopefully), and added some soft diode clipping to the feedback path. Tried a bunch of filters, but I'm terrible at filter math (and math in general) and combining low pass with high pass. Put that aside for now. Sounds good as-is but it still needs a variable filter.

Got modulation working tonight! Sine table on its own timer, gets scaled (speed and depth) and then added to the main samplerate. Goes from several seconds slow, to shy of ringmod speeds. Will do clips tomorrow!

Stuff left to do

-try pitch shiftagain (with bicolor led to show pitch up, down, or not at all)
-digitally rebias adc to 0 (because I redid the analog stuff)
-try filters again
-digital erosion filter. basically copy-paste code from previous project
-hold mode toggle from momentary stomp
-remember if was in hold on power up
-relay bypass logic.
-modulation LED (no more timers for PWM, maybe make 3bit R2R ladder from 3 free pins)
-fine-tune time stretch/smear circuitry
-option to clear the loop when bypassed and holding hold
-other stuff I'm sure. careful of feature creep

[anotherjim]

Loads of filter calculators here...
http://sim.okawa-denshi.jp/en/Fkeisan.htm

"Active filters" at the bottom of the list for your basic opamp feedback cap LPF. Multiple Feedback for the ones normally used with delays.

Check out the LM13700 for making variable filters. Simple unless you want accurate tracking like a synth filter. Plenty of designs out there. You could control it with PWM to match sample rate, but you have none left?

[Les Paul Lover]

Are you planning to include tap tempo too?

Most useful function in a delay IMO.

In any case, very impressive work!!!!!!!

[cloudscapes]

Loads of filter calculators here...
http://sim.okawa-denshi.jp/en/Fkeisan.htm

"Active filters" at the bottom of the list for your basic opamp feedback cap LPF. Multiple Feedback for the ones normally used with delays.

Check out the LM13700 for making variable filters. Simple unless you want accurate tracking like a synth filter. Plenty of designs out there. You could control it with PWM to match sample rate, but you have none left?

Thanks! I've found lots of calculators, this one seems to have more stuff though. Still, I'm inherently bad at math, so even with formulas and calculators staring me in the face, I still manage to screw things up.

I don't need the filter to track the samplerate or anything. It's a "coloring" filter, like a bandpass tone knob in the delay feedback. The hump doesn't need to be steep. But based on my tests this week, seems like I can't even get an imprecise bandpass to work.

Are you planning to include tap tempo too?

Most useful function in a delay IMO.

In any case, very impressive work!!!!!!!

I thought about it. Tap tempo isn't very useful to me, though. I like my delays a bit "off". If I do, it'll be if I make the momentary hold stomp multi-function, selectable by toggle or something.

[cloudscapes]

looks like this thing will have 13-14 knobs, two soft-stomp switches, a few LEDs, and probably at least one toggle!

big box time!

[cloudscapes]

A few new videos

filter test. I finally resorted to two seperate rc filters, one high pass, the other low pass, with their own opamp buffers. a pot blends between the two of them. the filter knob is the one in the lower left! fancy active filters make my head hurt, this works better for me.

modulation. variable speed from sea sickness to sub-bass rates. I get crackle when I set it too fast so I'll have to investigate. I suspect at that modulation speed it skips or misses some samples.

long delay feedback. set it to the longest mode (between 3.5 seconds and 14 seconds) and playing around with feedback, filters and a bit of modulation!

[deadastronaut]

nice...audio terrorism at its best..

[cloudscapes]

 

today / tomorrow, redoing the adc/dac filters (not the "creative"  tone filter). they were just passive rc filters. using filterlab to try and do something better.

also, still seeing if I can get the headroom better.

[cloudscapes]

my PIC32 code, for those curious
http://dronecloud.org/stuff/delay.html

[cloudscapes]

got samplerate reduction (as a blendable effect) done!

I gave up on pitch shifting, though. it made everything glitchy, even when the effect wasn't dialed in. just ther existence of the functions and changes I had to make made the ordinary delay part buggy. not worth it.

only have 5 things left on my to-do list (all of them easy), before I can start designing the control layout + pcb layout for the actual pedal!

[cloudscapes]

also, a quick mockup. temporary fonts, no design, etc. just for placement planning. gotta do this before I can start the PCB, since everything's going to be mounted on it.

[~arph]

my PIC32 code, for those curious
http://dronecloud.org/stuff/delay.html

Hey that is really cool. I always wondered what your code looked like. Looks very neat! I think you find the same that lost of comments are needed when coding this stuff as one can not remember all registers all the time. Good job

[cloudscapes]

Yeah, lots of comments help because I'm not *really* a programmer. Merely someone who knows programming. The register stuff makes my brain hurt, even the easy ones. I like code that looks like actual words, not strange hieroglyphics.

Currently working on blendable ring modulation in the feedback path! It's not a huge amount of work. An adaptation of the normal modulation timer (at audio rates, rather than LFO rates), using the same sine table as normal modulation, and then straight-up multiplying each signed audio sample with the current sine sample. If I get it to work and I like it, I figure it could use the same controls as normal modulation, "rate" and "depth". With a toggle underneath which assigns the controls to one or the other type of modulation. Shouldn't take more than a couple hours!

[cloudscapes]

blendable ring modulation in feedback path

so yeah... that's staying in! the sound of a ringmodded signal being delayed and folded over itself to oscillation is so awesome!

tiny bit of carrier bleed. I can fix that in software. maybe by (digitally) fading the carrier oscillator to nothing when the audio input level is near the bottom.

[glops]

Good god, that ring modulation!   

[cloudscapes]

Good god, that ring modulation!   

yeah, totally staying in!

it adds really interesting over/undertones when dialed subtly! but cranked, I get the amazingness at 2:35--
I can't decide which is more awesome