Developing a powerful digital looper project for the DIY community

[cardinalflyer]

You looking for something like this then?
http://focus.ti.com/lit/ds/symlink/dac714.pdf
http://focus.ti.com/lit/ds/symlink/ads7813.pdf

16 bit serial data in to DAC out in 16 pin DIP format.
16 bit serial data out ADC in 16 pin dip format.  40 KHz sampling, just what's needed for audio.

[scratch]

those are interesting ... I'll check out the price on Digikey, and see what is available in shift registers ...

[scratch]

You looking for something like this then?
http://focus.ti.com/lit/ds/symlink/dac714.pdf
http://focus.ti.com/lit/ds/symlink/ads7813.pdf

16 bit serial data in to DAC out in 16 pin DIP format.
16 bit serial data out ADC in 16 pin dip format.  40 KHz sampling, just what's needed for audio.

at Digikey the DAC goes for almost $47, and the ADC for $35 (cdn) ... going to be easier (and cheaper) to stick to the parallel ones.

[flo]

Imo designing both the hardware and software will be a large amount of effort (years probably).

Why not use:
- PC as computing platform. Its the most standardised computing platform with USB device support and user friendly OS environments.
- USB AD card. 16 bits AD with ASIO driver support go for 40 dollars or so these days, 24 bit AD for 100 dollar.
- Host software that support ASIO for low latency (a few ms is standard these days).

Then write the looper app in a nice high level language like C++ (like an ASIO plugin or VST-Instrument) or even graphically (for the non-programmers) using MAX/MSP or PD (pure data)?

But first find out that this has probably been done already by someone else, is readily available and probably freeware!

My advice:
Go laptop, or perhaps even a small netbook, install MAX/MSP or something and have loads of looping fun within a day!

[ExpAnonColin]

Maybe we should split this into a separate thread on good external A/D converters, but here's a very simple one, fast enough, and relatively cheap (~$9)
http://focus.ti.com/lit/ds/symlink/ads8320.pdf

And, it's also good to look at audio-specific ones, this one is stereo at about $5, and can do 48khz:
http://focus.ti.com/lit/ds/symlink/pcm1801.pdf

Unfortunately at this level of performance you have to start getting into smd.

-Colin

[cloudscapes]

yeah initially I didn't want to go with parallel converters because of all the pins they requie.
I guess I could use a port expander, though like the MCP23S17.

I tend to stay away from AD's surface mount stuff, because not only is it surface mount, it's the super tiny kind. I have one of their 8-pin DDS chips and it's almost too small for tweezers (grain of rice size)! no way can I solder those. not DIY friendly at all.


flo: I dont know, as far as I'm concerned, the point of DIY is to keep away from laptops
I like being limited and super-compact

I dont think it would take years to develop. I learned how to use dsPICs and how to input sound and output it again in just a few hours. add some storage and basic looping buttons and you've already surpassed most ISD-based loopers in a few more hours/days of R&D.

overdub is another story. the math in programming isn't hard, but in practice I'm eager to see how easily it'll clip.

[flo]

flo: I dont know, as far as I'm concerned, the point of DIY is to keep away from laptops

My suggestion was to use the PC/laptop as hardware+interfacing base. The actual looper software development part is still DIY, right?

[Taylor]

Hey guys, today I coded up a looper for the FV-1. The chip only has 32k of memory, which gives one second of recording time with 20hz-16khz frequency range - definitely not a looper. But, a clever guy at the Spin forum showed me a way to internally undersample the delay, which allows us to do some things I didn't think were possible with the chip.

Right now I've got it doing 8 seconds of delay at 4khz sampling (which means 2khz is the highest frequency it can represent cleanly). It's pretty aliased, ala chiptunes/Nintendo, but with 2 4-pole filters, one before and one after the delay, you can get it sounding more like an analog delay than bit crushed. I'm going to see how far I can stretch this - at 32 seconds, it would allow up to 500hz frequency response. This is known in audio circles as "completely f-ing terrible", but for the adventurous it might be fun.

Without filtering, 500hz will probably sound ridiculously aliased, beyond 8-bit NES stuff (yes, I know there's a difference between sample rate reduction and bit reduction). but with heavy filtering (which is easy in the FV-1) it will be able to represent the fundamental frequencies of most of the notes on a guitar.

So, it'll come out either crazy, ugly, or without any harmonics, but the amazing part is just that it's possible to get something like 30 seconds of delay time out of so little memory. This is far from what I had envisioned when I started this thread, and it will never be anything like a clean commercial looper, but if you're cool with lo-fi sounds, I think you'll enjoy this. "What makes this different from a LoFi Loop Junky/Payback-type looper?" you ask. Answer: even worse sound quality, and infinite layers of overdubbing.  

If anybody thinks they'd be interested in building this (perhaps after I can do some sound clips), let me know and I'll think about how to make it happen (at its simplest, you could build the Tonepad FV-1 board and I could send you an EEPROM chip with the looper code on it). Does that sound interesting to anybody?

[pazuzu]

i would try it.

[Strategy]

I would try this to.

Taylor, can the code be written so that the user could alter the amount of downsampling, from short, hi-fi loops to zonked, low fi, long loops?

This might just be the project to push me into checking out FV1. 

A short loop has its uses, too, like the "hold" on old digitech double pedal digital delays- very musical on the 2-second delay for instance. And those are NOT hi-fi, full bandwidth digital delays, they have their alias-hiding filtering, and its' very musical.

- Strategy

[Taylor]

Taylor, can the code be written so that the user could alter the amount of downsampling, from short, hi-fi loops to zonked, low fi, long loops?

A short loop has its uses, too, like the "hold" on old digitech double pedal digital delays- very musical on the 2-second delay for instance. And those are NOT hi-fi, full bandwidth digital delays, they have their alias-hiding filtering, and its' very musical.

- Strategy

Yep. Coding it as a continuously variable control would be a bit hard, but what we could do is use the switch inputs to select between some preset sample rates. Depending on whether we need a switch for anything else, there could be up to 8 different sample rates.

Keep in mind I just did the first code and tested it today, so the concept isn't all that fleshed out, but I was thinking a knob for delay time, a knob for filter frequency, and a knob for feedback/repeats. Then a rotary for sample rate. Ideally I'd like to do a stomp switch to set time like a real looper if I can figure it out, but at least for now it just works like a really long delay - you set loop length with the delay time knob.

I really recommend the FV-1. It opens up a ton of possibilities outside the reach of analog DIY. There's definitely a learning curve, but it's actually pretty easy to get into.

[Strategy]

Preset sampling times is good. If you develop the project more, I might be into trying it, but my backlog is mighty. That said, Where's The Party At and Tau Pipe Phaser are both almost done (for reals this time) so who knows, maybe I'll be able to start digging into this.

Will keep watching for updates on this

- Strategy

[wavley]

I would try this to.

Taylor, can the code be written so that the user could alter the amount of downsampling, from short, hi-fi loops to zonked, low fi, long loops?

This might just be the project to push me into checking out FV1. 

A short loop has its uses, too, like the "hold" on old digitech double pedal digital delays- very musical on the 2-second delay for instance. And those are NOT hi-fi, full bandwidth digital delays, they have their alias-hiding filtering, and its' very musical.

- Strategy

I still use an RDS-900 (rack version)  I've tweaked it so it will go to about 1.5 seconds, it has it's uses.  I have a boomerang+ and 16 sec in my rig and I still use the RDS for a lot of stuff.  It gets a grainy/pixilated sound at longer delays that I like, not to mention the built in LFO and the voltage control delay time, it can get real fun!

[Taylor]

Preset sampling times is good. If you develop the project more, I might be into trying it, but my backlog is mighty. That said, Where's The Party At and Tau Pipe Phaser are both almost done (for reals this time) so who knows, maybe I'll be able to start digging into this.

Will keep watching for updates on this

- Strategy

One cool thing about the FV-1 is that the hardware doesn't need to change to build a completely different effect. So if you build this looper, you can also download tons of other programs and have other interesting effects available without having to build a new pedal. It's also way simpler to build than WTPA or any Juergen Haible stuff. Definitely interested to hear about those two builds, BTW.

Does anyone have any thoughts about other modes or features that would be fun with this? My plan has already used up the 3 available pots, however I have worked out a trick to get a 4th pot, so what else could we add? A vibrato ala the LoFi Loop Junky is possible, but it would have to have either the speed or depth preset, or else have them controlled by the same knob (giving you slow shallow vibrato, or fast deep vibrato, or the other way around). Or if I do work out a solution for a record/play stomp switch, it would probably use this 4th pot.

Any interesting suggestions welcome.

[Strategy]

Vibrato is good- I was thinking filter cutoff freq controllable by potentiometer. On the other hand, it seems like a pedal like this could have analog stages in the same box, even a simple tone control would be useful or the Escobedo Q&D VCF...

I plan on doing comprehensive build reports for the mega projects WTPA and Tau!

- Strategy

[Strategy]

I'm curious about this? Do you mean Digitech RDS-1900? And it has voltage control - like a CV input for delay time?!?

- Strategy

I still use an RDS-900 (rack version)  I've tweaked it so it will go to about 1.5 seconds, it has it's uses.  I have a boomerang+ and 16 sec in my rig and I still use the RDS for a lot of stuff.  It gets a grainy/pixilated sound at longer delays that I like, not to mention the built in LFO and the voltage control delay time, it can get real fun!

[Taylor]

Vibrato is good- I was thinking filter cutoff freq controllable by potentiometer. On the other hand, it seems like a pedal like this could have analog stages in the same box, even a simple tone control would be useful or the Escobedo Q&D VCF...

I plan on doing comprehensive build reports for the mega projects WTPA and Tau!

- Strategy

Yep, I've already got the filtering controlled by a pot right now. A tone control or simple analog filter really won't do here - you need a very steep filter to cut the aliasing while allowing the instrument to come through. Right now I have two 4-pole filters, one before the delay and one after.

BTW, any pot on the FV-1 is a CV input, so (with some caveats) you could have CV control over delay time, filtering, and feedback if you wanted to, without any real modding.

Oh boy, my next post will be the mythical 1337! I think that's the post # after which DIYers become men.

[Strategy]

CV inputs? Well that is badass. FV-1 is now really really appealing. Is there a noob guide or how-to-get-going thread?

What are the caveats for CV input?

- Strategy

Yep, I've already got the filtering controlled by a pot right now. A tone control or simple analog filter really won't do here - you need a very steep filter to cut the aliasing while allowing the instrument to come through. Right now I have two 4-pole filters, one before the delay and one after.

BTW, any pot on the FV-1 is a CV input, so (with some caveats) you could have CV control over delay time, filtering, and feedback if you wanted to, without any real modding.
[/quote]

[Taylor]

Well, one is that there is about 100ms delay on the pot inputs. This makes no difference when adjusting them with your fingers, but if you were sending a time-synced LFO or something into the pot inputs, it would be delayed by a 10th of a second, which might be a problem. The "4th pot" trick, which uses one of the audio inputs as a pot input, does not have this delay, but you can't send a regular CV into it, unfortunately.

The other thing is that the CV needs to range between 3.3v and 0v, so for most things you'd probably need to attenuate the CV if it's 0-5v.

The best noob guide is to check out the knowledge base at the Spin Semi website, and read through the forums a bit. I would be happy to help out with any questions you have about getting started with it.

[Rectangular]

my favourite "loopers" are japanese sampling delays from the 1980s.  they provide a maximum of 1 second sampling time, but there was always a good selection of different overdub and truncate features, depending on the make/model. also, because they were pre-midi, there were inputs for realtime control of sample length and speed.  it is my goal to one day reverse engineer one of these, so that I can make them myself, possibly with more sampling time.. you simply cannot beat the sound. I don't like any of these new 24bit samplers... as far as I'm concerned, nothing beats that 12-bit punch.

the best ones tend to be the most rare/esoteric, but check out the Boss RSD-10 and Arion DDS-1, you can still find them occasionally.