Developing a powerful digital looper project for the DIY community

[wavley]

Well, something like the boomerang+ (my favorite looper) uses some sort of analog devices dsp and a stick of memory from a 486 or something it also has a foot roller for loop volume which is where an expression pedal might be handy.

I was messing with the variable speed with exp pedal on my rds-900 last night and it is awfully fun.

I don't know much about digital but I'm in for whatever I can help with on this project!

[Taylor]

Just a quick thought:

Revisiting the idea of using the ISD recorders, what if we placed an exciter circuit after each recorder, to add back what's lost each time in the a/d/a conversion? After all, the exciter was invented to add back/resynthesize high end to tape recordings with many overdubs. That's basically what we're working with here.

This would never sound like an RC-2 or similar, but for something a little strange but without total mud, it might be cool.

[cloudscapes]

I just got myself a dsPIC kit with the express intent on doing some mid-fidelity (12-bit) looping and sampling in its many forms. I intend on using an MCP4921 DAC as it's well documented, cheap and seems to be a norm among PIC users. storage is a little trickier. I don't think using RAM chips is going to be feasable since they usually employ huge address bits (19+ bit) which means either using 19+ pins on the MCU or doign some tricky binary counting stuff I'm not ready to go into. anyway I need the RAM to be random access, not sequential, putting binary counters out of the picture.

I'm looking at using memory cards for storage. SD/MMC is a good candidate since it only uses like four pins to communicate with the MCU (via SPI). need to buffer 512 bytes worth of sound and dump it all at once on the card while filling up another 512 byte buffer in the meantime.

I was using AVRs previously which would of probably been good for 8-bit looping, but having the dsPIC's 16-bit pipe instead will be a huge help for better fidelity. in fact since I'm using 12bit conversion, there's a full 4 wasted bits that have absolutelly no concequence on the speed of the processing! if I find the *right* 16-bit DAC and ADC, it would cost no more than 12-bit. I'm just using 12-bit now because the chip has in-built 12-bit ADCs and I'm just learning.

I'm using the mikroBasic compiler because I'm not smart enough for C.

[Taylor]

Cool, interested to see what you come up with.

I was also interested in this:

http://www.diystompboxes.com/smfforum/index.php?topic=74742.msg661285#msg661285

[jessej]

I found this last night and just thought to pop this in here because there are probably people here who will enjoy this finding very much:

Mobius - the programmable looper
http://www.circularlabs.com/index.html

It is free and available for both Win/OSX, both standalone and VST/AU.

[cloudscapes]

Cool, interested to see what you come up with.

I was also interested in this:

http://www.diystompboxes.com/smfforum/index.php?topic=74742.msg661285#msg661285

yeah that sampler looks completelly nuts! just a 40-pin AVR, a resistor ladder and some RAM. great design!

I held off buying it because not having one gives me further incentive to learn how to eventually make my own

I notice a lot of lo-fi loopers and samplers use 74lc ICs for address latching. I can't helt then agging feelign that I should learn what these are about. I've tried the datasheets, but still can't "visualize".

[dellamorte]

http://little-scale.blogspot.com/search/label/eprom%20music
found this the other night it sounds interesting

[Strategy]

I'll post a report on the Where's The Party At Sampler (mentioned by Taylor a few posts ago)

I just populated it and ready to solder, I forgot to order a couple parts so it may be a few weeks...

Its not really a "pedal" without a MIDI foot controller (which I would like to DIY as well if such a project exists)
more exciting is that a friend of mine, an engineer who recently built a custom midi controller for me said he's working on a small sampler
I'll try to connect him to this thread although he's really busy with a Linux related day job. He uses mainly AVR for his embedded projects. He said something to the effect that he had to program the RAM functionality himself, I'm really dumb about digital so you'll have to bear with my loose description but he basically said he had to write the protocol for the way the RAM chip gets stuff written into memory because there wasn't an exactly right sort of product out there "out of the box." I do not know where they are with this project. He works with an interesting shop here in portland that sells one of a kind, really extreme pedals and touch synths:

www.buzz-r-electronics.com

- Strategy

[Taylor]

www.buzz-r-electronics.com

Aha, I have run across this guy - I have a feeling he'll be selling about 5 Gristleizers pretty soon...

Doesn't the WTPA? have onboard switches for rec/play/etc.? If so, couldn't you just wire up some momentary SPST stomps to perform these functions without MIDI?

[Strategy]

yes, you could totally wire up spst momentary's, no problem, but there's even more stuff you can do with MIDI than from the front panel, so that was my rationale with that (and I'd love to have a MIDI foot controller any way.) So for pedal builders that would be a good route to go. I want my WTPA? to double as a desk top module. About half the time I play shows I am using table top gear like drum machines etc. So my pedals have to be desk friendly and my desk gear has to be foot friendly when I play 'live' instruments.

Buzz-R-Electronics is awesome. I have bought a bunch of stuff from there. The guy who runs it is a long time experimental/improvisation community person here who I have played with a bunch. Glad they will have gristleizers!!

I will ask Alex from Buzz-R about their sampler project.

- Strategy

[scratch]

I've started going through Digi-key and Mouser looking for 16bit ADC's w/ parallel output ... not an easy task and not cheap ...

Would any of these work?

http://focus.ti.com/apps/docs/viewdevices.tsp?blockDiagramId=6017&blockId=8833&designOptionId=10005&appId=376

Or

http://www.analog.com/en/analog-to-digital-converters/audio-ad-converters/products/index.html

Both of these companies offer freebies to build prototypes 

Does this help???

sorry for taking so long to answer, but no these don't work in terms of the project posted at little-scale ... it uses parallel interface ADC/DAC, it makes easy to interface directly to the SRAM. The ones you posted are Sigma-Delta converters, an encoded serial 'bitstream' output which would require additional hardware to process to store in memory and recall. These I wouldn't know how to use even if they are cheaper. The parallel 16bit ADCs and DACs I'm looking at so far go for approx. $23 each.

[ExpAnonColin]

Apologies on being a late-comer but you aren't going to be able to use a PIC or AVR and expect to get a looper that is not basically a toy (eg, low-bit sampling and low sample rate).  You can get some very cool stuff like the Where's The Party At but nothing even close to commercial quality.  For that, you'll need a DSP chip or some other much faster platform - maybe a 16 or 32 bit system, at the least.  The AVR32 and dsPIC might be able to do it but those are a totally different beast than AVR or PIC.  You would probably be better off looking into a more well-accepted platform, like TI, maybe TMS320C55x, with an external ADC and RAM (SD card would be smart).  But really embedded DSP is not at all well internet-documented, so it will certainly be an adventure!

-Colin

[cloudscapes]

yeah the best I was able to do with regular AVRs was 8-bit mroe or less 20khz, and there were clicks every few fractions of a second because of the buffering I had to constantly do.

I've been doing tests with a 16-bit dsPIC (F30) since last week and this thing is a BEAST in comparison. I'm doing 12-bit sampling at 90+ khz 
still wont be pristine though, because of limited headroom.

[MoltenVoltage]

embedded DSP is not at all well internet-documented, so it will certainly be an adventure!

+10

[ExpAnonColin]

I've been doing tests with a 16-bit dsPIC (F30) since last week and this thing is a BEAST in comparison. I'm doing 12-bit sampling at 90+ khz 
still wont be pristine though, because of limited headroom.

What language are you writing on the dsPIC?  Why 12-bit, because that's the built-in ADC?  And what do you mean about limited headroom - you mean because you're sampling at 12 and not 16 or 24 bit, or because of 5v?  Because if it's the latter, just attenuate and reamplify!

-Colin

[cloudscapes]

What language are you writing on the dsPIC?  Why 12-bit, because that's the built-in ADC?  And what do you mean about limited headroom - you mean because you're sampling at 12 and not 16 or 24 bit, or because of 5v?  Because if it's the latter, just attenuate and reamplify!

-Colin

in basic (mikrobasic compiler). I can't seem to ever get my head around C when I look at it.

12bit because I already had 12bit DACs lying around that are incredibly simple to use. I looked for 16bit (and over) converters but they all seemed to be much more complicated to use, with compression and SMD leads. for now since I'm just learning this new platform, I'll stick with simple.

yeah, lower headroom because of the 12bit. currently I am attenuating and reamplifying, but a bunch more noise adds itself. I've ordered some 12bit ADCs which I guess will have less noise than the internal ones I've been using.

[ExpAnonColin]

in basic (mikrobasic compiler). I can't seem to ever get my head around C when I look at it.

12bit because I already had 12bit DACs lying around that are incredibly simple to use. I looked for 16bit (and over) converters but they all seemed to be much more complicated to use, with compression and SMD leads. for now since I'm just learning this new platform, I'll stick with simple.

Yeah, once you get into 16 bit ADC's normally you have to deal with a serial output, which is not so bad once you get used to it. If basic has macros for I2C then you can definitely get a 16 bit ADC which communicates over that.  Or even SPI.  You might head over to AVRfreaks and ask them if anyone is using a 16 bit adc with an avr.

-Colin

[cloudscapes]

Yeah, once you get into 16 bit ADC's normally you have to deal with a serial output, which is not so bad once you get used to it. If basic has macros for I2C then you can definitely get a 16 bit ADC which communicates over that.  Or even SPI.  You might head over to AVRfreaks and ask them if anyone is using a 16 bit adc with an avr.

-Colin

well, I'm not to irked by SPI. the DAC I'm using is SPI and it's been pretty easy to use. I guess it's just that if I choose a 16-bit DAC/ADC instead, then I can no longer put all control bytes and data bytes in a single 16bit word. I'll have to do a few control bits first, then wait, then the data. to someone like me who's just learning, it doesn't fit in as neatly a tight package.
I'll eventually get to 16 bit, and I'm sure dsPICs can do 24bit even, but for now I'm gonna stick with this. 12bit is nice.

I guess it's also the surface mount stuff that puts me off. I haven't found any SPI 16bit converters in DIP

[cardinalflyer]

There's these, both 16 bit in DIP
http://www.newark.com/linear-technology/ltc1605cn-pbf/16bit-adc-1605-dip28/dp/38K4125
http://www.newark.com/texas-instruments/dac715p/16bit-dac-pdip28-715/dp/61M5731

Not inexpensive ...
Robert

[cloudscapes]

There's these, both 16 bit in DIP
http://www.newark.com/linear-technology/ltc1605cn-pbf/16bit-adc-1605-dip28/dp/38K4125
http://www.newark.com/texas-instruments/dac715p/16bit-dac-pdip28-715/dp/61M5731

Not inexpensive ...
Robert

thanks Robert
unfortunatelly they're in parallel interface. not bad for speed and simplicity, but I see that more as a last resort since it'll use so many MCU pins.

I'll still write them down, in case....  

and I havent checked neward before, guess I'll browse a bit