Crap Me Up – 8bit lo-Fi sampler


It’s more a preparatory work for a possible 8 bit sampler project than anything else. The idea is to collect datas from the ADC (and an incoming signal), store the datas in an array (SRAM), and play it back with a variable speed (external oscillator)

To make things funnier I want to incorporate some “tweak” knobs. 2 of them being “start” and “stop”. They determine the start and stop positions for the reading of this array. A counter (index_view) browses through the array whithin those limits. sampler_arrayA second effect can be added to reverse the direction, we reverse the browsering and go from stop_index to start_index.

Then the datas are sent into the I2C bus through timer1 counter interrupt which is clocked by an external variable clock. The idea behing that is to reduce or increase the speed of outputing the datas (DAC) and create a higher (or very lower) pitch. Here’s the hardware (much simpler):

crap_sampler_jpegICA amplifies the signal to reach 5V peak-peak signal for the converter (set by the gain pot). The bias is applied to put the output a 2.5V. R13 is used to set the offset (if there is any). IC2A is a buffer (I think the input impedance of those ADC are a bit funky).

Once the signal is out from the DAC, it is mixed with the original. The overdub signal is then send back to another ADC to record an overdub with the previous sample.

Obviously, the atmega 328 isn’t made for that kind of work. Although its SRAM is enough for most of the micro-controller work it isn’t suitable for recording a storing so much datas. But ! the use of an external SPI (or parrallele) SRAM is possible, as the Microchip 23A256 SRAM. I don’t if a SPI or I2C protocol may cause delay (maybe not enough if the clock is very high)

Storing a sine wave and select only of portion can create several kind of waveforms. Could be handy for a LFO or VCO (and both) whilst being light on memory use.

C code :

So, I don’t know if that project would see its birth coming soon however it could be interesting to build such lofi-dirty sampler. Not only it could be used as stand alone silly voice modifier-sampler but could be also tweaked to fit the modular synth aesthetic. It could also be interesting to use a more powerful microprocessor (STM32 or FPGA if they weren’t that expensive?) and leave the 8bit format for something with higher resolution (with less appeal ?). This will have the beneficial side-effect of learning something new which is always good !

SPI SRAM 23a256:

EDIT 11/08 : the work is coming good, the reverse reading works great. Obviously, clocking the  MCU with only 8Mhz is far from being optimun but for debugg work is still good to start the overall working of the code. THe input may also need a proper RC filter to kill noise above 20khz (and avoid even more crap)



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3 responses to “Crap Me Up – 8bit lo-Fi sampler

  1. I saw this vid and it crossed my mind that you might find it interesting. Ia might be possible to make an analogue Sampler using floppies.

    But going back to an 8bit sampler, it might be worth including a 2to1 compressor in the input and 2to1 expander on the output, this should improved distortion and signal to noise ratio but it does introduce errors in the dynamic range.

    Regards Bishka

  2. yeah, Jeri Ellsworth is very fascinating, very Inspirational as well. I’ve been following her work for several years now and it is very interesting. One of the most mindblowing was her home-cooked transistor. She’s working on a new kind of Virtual Reality, “cast AR” right now which was “kickstarted” with great success.

    Good idea for the compressor/expandor, I haven’t though about it. But I think I’ll put this project aside while I’m finishing my other projects. I think it might be worth it to go to ARM stuff. Although the market is fully populated with lot of different dev boards and it could be hard to chose the higher resolution may be better. But as always with digital stuff, need a programmer, a new toolchain/sofware to learn…always nice to discover new land but it needs time.

    Thinking about floppy disks, It makes me think that the use of old tape cassette could do the trick as well if one can get all the mechanical stuff from a walkman or a thing like that ! I remember an article in Stompboxology about a tape delay with that idea. Could be very interesting to do and I’ve some cassette in my junk (I’m feeling old talking about cassette…). And yet another project to test hahahaha

    But Could be a really neat thing to do for the retro-hipster scene hahaha

    anyway, thanks for your interest in my silly things Bishka !!

  3. I like your ‘silly things’ They are getting me interested in electronics again after more ten years absence!!


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