analog bit crusher

[Br4d13y]

http://www.aronnelson.com/gallery/main.php/v/Choklitloves-album/album16/analogbitcrusher.png.html

has anyone built this? i would like to know  how it sounds, because it sounds like a fun pedal to me

[oldrocker]

I built it but not using this layout so theres no verification here.  I perfboarded it using 2 separate dual op amps instead of the LM324.  I works great and sounds similar to the Nyquist but much easier to build although the Nyquist is much more versatile.  This layout looks like the one I built though except for the op amp substitutions.  One knob frequency adjustment makes it easy to dial in the crazy sounds.

[Br4d13y]

what two op-amps did you use

[sean k]

Good explanation here of a sample rate reducer.( by the man who designed the above)
http://www.experimentalistsanonymous.com/board/viewtopic.php?t=1127
The original schematic is in the experimentalists anonymous archives under noise makers.

[oldrocker]

I used 2 TL082's.  Colin R. suggested separating the op amps in his notes for the design.

[oldrocker]

The schem below shows some mods that I thought sounded better to my ears.  R7 changed from a 100k to 47k.  C4 changed from a .0033uf to a .1uf cap.  And I used GE 1n34 diodes instead of the 1n914 SI's.

http://i218.photobucket.com/albums/cc93/ftrock/untitled.jpg

[Br4d13y]

i'm not very good at reading ic's... is x1 pins 1 & 8?

[lotsolowend]

any chance we can see your perfboard layout, or did you just go straight from schem to board?

[darron]

The schem below shows some mods that I thought sounded better to my ears.  R7 changed from a 100k to 47k.  C4 changed from a .0033uf to a .1uf cap.  And I used GE 1n34 diodes instead of the 1n914 SI's.

http://i218.photobucket.com/albums/cc93/ftrock/untitled.jpg

sorry to bring up something old....


i built this today and couldn't get it to work until i made the 100k lesser resistance with my fingers, and ended up changing the circuit to these exact values too (47K, 100n).

i used 2x 4558d chips for now. will probably use a lm358 for clock and a tl072 for buffers later as these would be better suited.



it's on breadboard and the clock signal almost bleeds through louder than the guitar. i'm hoping having it on a thoughtful PCB fixes this or can you always hear it?

ALSO, the pinout on the J201 doesn't match what i have seen in the pcb layout? i've read other people have had that problem.

if it works then i might try simple jfet buffers instead of opamps. to combat the clock noise could you possible have the opamp have a gain of say 10 then divide the volume later to combat clock noise?

any more thoughts on this project? i have a feeling people have found some better values... pretty cool if i can get it going properly (:

[cloudscapes]

bit crushing can't be made analog.  that's what the 'bit' is there for. it's the removal or rearranging of digital bits after conversion.

samplerate reduction however is another story, and that's what I think this pedal really is.

sorry, minor pet peeve.

[Taylor]

Actually, Etienne, it's possible to make a waveform that's functionally equivalent to digital bit crushing with analog components. Although we can still call it a misnomer (and I often find myself on forums making the same objection you're making), the result can be the same.

You're right that all of these things that call themselves analog bit crushers are sample rate reduction simulators, more accurately. However, you can take the front end of a flash ADC circuit (just the bit with the comparators), mix the outputs of the comparators together and you have a waveform that is quantized on the amplitude axis, just like digital bit crushing.

You get 3 "bits" with 8 comparators.

For the sample rate reduction sound, which this "analog bit crusher" is actually meant to do, I really like The Tone God's Crazy Larry. It has a gate that kills the oscillator when you're not playing, which is really nice because all of the other ones (and I've built many) have bad oscillator bleed. I have a PCB for it that should be ready soon.

[darron]

bit crushing can't be made analog.  that's what the 'bit' is there for. it's the removal or rearranging of digital bits after conversion.

samplerate reduction however is another story, and that's what I think this pedal really is.

sorry, minor pet peeve.

well, this example isn't 100% bit crushing, but the holding effect has the exact same laddering appearance on my scope, just at an infinite number of bits (:

i was wanting to build a real one, but i thought this would be easier than trying to generate the -15v for the ADC/DAC. this you can build with stuff you have lying around.




i'll take a look at the crazy larry, but again i liked the simplicity of this circuit.

i noticed that when i disconnect the clock from the fet, the bleedthrough is just as loud as connected, so hopefully its capacitance in the breadboard. i might try making a board to seperate the two and then put lots of earth in the middle.


the noise gate probably isn't a bad idea either because the old atari sounds had a very hard attack and decay i suppose.

[Taylor]

well, this example isn't 100% bit crushing, but the holding effect has the exact same laddering appearance on my scope, just at an infinite number of bits (:

What you're seeing is quantization along the time axis (sample rate reduction). Since pitch is cycles per time period, this kind of quantization creates new pitches (see Nyquist). Quantization on the amplitude axis (bit crushing) is just a type of distortion - it doesn't create new inharmonic pitches. So although it might look similar in that it makes a waveform stepped, the sound is quite different. Real bit crushing really just sounds like distortion.

[Earthscum]

...

Real bit crushing really just sounds like distortion.

While we're on it... what would it be considered if I take 2 PWM's, hook them up so they only oscillate when there's a signal coming through at the trigger level (basically the input was turned into a square wave, then introduced as a 3-state signal... digital gate of sorts). The output that I was trying to achieve was a 1k oscillation between I-Off and 0-Off. It basically sounded like a distortion with a 1k ring mod (rather annoying, I might add, but it worked as I had planned). Is this similar to what real bit-crushing is? My next step on that circuit was to introduce a F/V converter to vary the pulse width (oscillation), but I apparently didn't write any notes down, so I gotta design all over again, and hopefully remember how I did it.