'TinyRhythm'

Multichannel Midi-Triggerinterface with onboard digital drumsynth

Cymbal / Cowbell

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The by far most complicated module for the TinyRhythm. The noise/timbre it generates is sent through an analogue bandpassfilter and an analogue vca with an adjustable, nice looooong decay. The frequency of the bandpassfilter is altered by the light of a LED which shines on a lightsensitive resistor.

First i want to tell you where i lost my fear about 808-schematics-analyzation - it's the very interesting site of eric archer. His page about the analog 808 cowbell inspired me for the creation of this module.

Functionblocks

This module reads 3 ADCs for Trigger, Tone and Modulationmode.

It outputs a trigger to the analog envelope and noise/spectra/cowbellsound.

Trigger: the triggerintensity has influence on the negative-high triggersignal the tiny13 sends to the analog envelope modulating the VCA. The higher the incoming trigger, the 'longer' i made the outgoing trigger. The envelopecapacitor has more time to load up resulting in more energy in the envelope -> a deeper envelope depth. Well, thats the theory, in practice it works but not as perfect as i expected. The capacitor charges to fast for the time. my mainloop need for one circle. Although there IS a very nice difference between low and mid triggerdepth, no real difference between mid and high can be heard. Some parts should have been altered to improve this. Maybe sometime ...

Tone: The Tone-pot has from middle to the left my beloved shifted noise which can be tweaked from kind of white noise to a sparkling darknoise. To the right i implemented 3 cymbal-like spectra and 3 cowbelltunings which are produced by 3 square-oscillators, made in software of course. The tiny13 does not have any envelopes or oscillators, its all software, quite simple software btw :)

Modulationmode: This pot is responsible for the LED behaviour. The brighter the LED gets, the higher is the cutofffrequency of the bandpass. I implemented the four most useful modes for the LED-fading:

• sample and hold: each time a trigger comes in, a random value which alters LEDs brightness is stored until next trigger
• lfo: simple trianglewave fades LED, speed can be altered
• envelope: i made a positive and a negative one, speed can be altered
• full brightness: usefull, because i used one pot to aöter the modulation depth of the LED on the filter. I couldn't manage to solve this in the LED-driver, so i put the pot in series to the ldr, pulling it towards mass. Works quite good.

functional diagram for cymbal/cowbell-module

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Bandpass altered by light

The idea is not very new. There are lots of diy-projects about oscillators altered in frequency by a lightsensitive resistor (called 'LDR'). I must admit, i am not a big friend of these ennoying noisemakers, they quite make me nervous with their everscreaming pointless soundcrap, uiiiuuuuiiiiiiiiuiiuiuiuiiiiiiiii.

Anyway, inspired by eric archers (see link above) brilliant analysation of the real 808-cowbell i wanted to bring the LDR together with a filter. The tiny13 has already left enought flashram to implement the fading of a LED by pulsewidthmodulation (PWM). So why not send an LFO to the LED? Or even an envelope?

the basic ingrediants - an old LDR, a housing which prevents light from hitting the ldr and of course a nice bright led

... well ONE led was to dark to push the LDR-BPF-combination high enough in frequency. i added a secaond led in parallel - much better

both are then stuffed together in the old din-jack-hull.