How do we start and please list some advantages to using digital circuits?

[aron]

Is this "affordable"?
Is it fast enough to handle our audio; i.e. can I make a digital stompbox?
Is there a kit?
Do I have to be a software programmer to do this?
Are there examples of source code?
Do I have to use a Windows Computer? 
Is this going to replace my analog pedals?

Thanks in advance!

[Roobin]

Is this "affordable"?
Is it fast enough to handle our audio; i.e. can I make a digital stompbox?
Is there a kit?
Do I have to be a software programmer to do this?
Are there examples of source code?
Do I have to use a Windows Computer? 
Is this going to replace my analog pedals?

Thanks in advance!

Sounds like a good idea. Possibly a Digital DIY FAQ from one of the guys (or gals) in the know.

[Peter Snowberg]

Is this "affordable"?

It is now.

Is it fast enough to handle our audio; i.e. can I make a digital stompbox?

Digital for control is not, but DSPs are. You can make a digital stompbox, but chances are that you will want to take advantage of places where digital can offer an advantage and leave the rest up to analog. The signals are analog after all.

Is there a kit?

There are many. For getting started with the Atmel AVR series of microcontrollers, I would recommend the Atmel supplied STK500 which I think you can get at Digikey for $79. It supports a lots of devices and makes getting going pretty easy. There are lots of kits for different chips out there and many programmers that you can build out of a handful of parts if you're on a serious budget.

Do I have to be a software programmer to do this?

I'm sure as time goes on there will be pre-programmed chips available from a number of people so you won't need to program in order to build cool things, but you will need to program if you want to design your own new things.

The Wavefront AL3201B DRE or Digital Reverb Engine is a perfect example of a pre-programmed chip. You just solder it in place and feed it a program number. The reverb processing is automatic beyond that.

There are lots of programming languages available from C to BASIC to assembly and many many more that are customized for particular types of control tasks. It's easy to get started and inexpensive these days. There are lots of getting started with microcontroller sites. We don't want to replace their functionality, but rather add a site that shows how to get started with digital and effects.

Are there examples of source code?

There will be many examples you can drop into place and use or modify. People give away microcontroller code just like they give away DIY effect schematics.

Do I have to use a Windows Computer? 

No, but Linux is the next best supported platform after Windows and most of the tools out there are windows based. We'll have to get some good tool lists together in a sticky post for all platforms.

Is this going to replace my analog pedals?

Never, but digital will sure add things we could only dream of 20 years ago. DSP is an additional option and not a replacement, that is unless it gets the job done better.


Thanks again Aron! This is going to be a great year for DIY! 

[SeanCostello]

As far as replacing analog, depends on the application:

DISTORTION: No. The cost efficiency of something like a Tube Screamer, compared to oversampled nonlinearities in the digital realm, makes your average analog distortion/fuzz/overdrive a real bargain compared to the digital version. The digital versions can select between different models, but for a DIY builder, it is still probably more cost effective to just build several distortion circuits and put them in a single box.

BOOSTER: No. Just use an op amp or something.

SIMPLE DELAYS (chorus, flanger, slapback): Not yet. The Chinese BBDs, plus the Princeton delay chips, makes the DSP solution a little more cumbersome and expensive.

COMPLEX DELAYS (multitap, reverb, looping): Yes. DSP starts becoming a more efficient option when you have multiple delay taps. Complex delay line modulation, unitary feedback, all sorts of good things.

AMPLITUDE MODULATION (ring mod, tremolo, frequency shifters): Maybe. Tremolo works fine in analog. Ring mod can work OK in analog, but is really smooth in digital, with all the carrier rejection you need. Single sideband amplitude modulation is a breeze in digital.

FILTER MODULATION (phasers, VCF): Maybe. For a simple 4 to 6 stage phaser, use analog. Voltage controlled filters are still cheap to build with OTAs, and the resulting tasty nonlinearities are difficult to simulate in digital, and need a lot of cycles. For highly parallel filters (bandpasses in parallel), or for complicated modulation, DSP can be useful.

PITCH SHIFTING: Yes. Even a simple overlap-add pitch shifter is made much easier in the digital realm. If you want to eliminate glitches, you need period tracking, which is best done in DSP.

HIGHER ORDER FILTERS (multiband, cabinet simulation): Yes. DSPs excel at this application. Getting several hundred cascaded or parallel biquads is no problem with the SHARC or Blackfin from ADI, and the same probably applies for the TI chips. The Motorola chips are a little less powerful, but probably have enough cycles for a fairly complex cabinet simulation.

FREQUENCY DOMAIN: Yes. Not really an option in analog. Last night, I got a 256-band distortion working on the SHARC. Crazy sounds - sort of a cross between a compresser and an aural exciter. Not necessarily useful for pedals, due to the inherent delay in FFT/IFFT processing, but still neat stuff.

These are the immediate pedal needs that come to mind. There is a world of digital algorithms that I have never seen in pedals, that might result in cools sounds.

Sean Costello

[puretube]

Is this "affordable"?
Is it fast enough to handle our audio...

yes - it is fast enough to make a CD quality copy of the guitarsignal,
and repeat that signal a good amount of milliseconds later...
nice for delay!
it can also store it in the same quality for more than just seconds...
great for looping!
it even can store it infinitely...
superb for sampling!

I`ll never forget the day, that the designer of the first <300$ sampler visited my home
in the early 80`s, and sold me one of his last handsoldered ZX81 based 8bit machines.
I rightaway built me a hardware-sequencer out of xxx diodes, to replace the cassette-based boot-sequence for my DIY souped-up to 64k RAM "computer"...
This thingy proudly enabled me to record a rap-tune with a now 79 year old artist (actually a painter/bongoplayer/violinist/teethless "singer")...

That first guy went to design the Hex-pickups for Shadow, the Blue-Chip (Axon) git-synths, before heading over to AKAI`s sampler adventures...

Yes, I bought an S612 for my studio later - to find out both devices were easier to work with, than the tape-splicing experiences in the 60`s...
(only missing the "natural" fading/phasing, and through-zero-pasteing of the tapes).

Yes - somebody please "build" an algorithm for diagonally cut tape-loops! 

[The Tone God]

I'll throw my $0.02 in. I'll gear my answer towards those looking into entry level microcontrollers e.g. PIC, AVR, STAMP, Rabit, etc. Others can reply for their preferred platform or DSP.

Is this "affordable"?

It depends on what you want to do. This defines what hardware and software tools you need. If you want to do simple things like blink LEDs then this is fairly cheap. If you want to build a full featured switcher then it will cost more. There is also the cost of YOUR time YOU will need to put into learning. YOU have to decided that cost.

Is it fast enough to handle our audio; i.e. can I make a digital stompbox?

Depends on what you are doing and what is "it" meaning the uC in question. Do not expect to make a cheap and easy one chip stereo chorus using a single little 8-bit uC. It will not happen as it is not the right tool for the job.

Is there a kit?

Most manufactures offer evaluation/development kits. Many third party options exist as well.

Do I have to be a software programmer to do this?

No but you will have to become one so starting with a programming background does help. Even the knowledge of basic programming techniques like loops, decession statements, the ability to translate between decimal, hex, and binary helps a great deal. The rest become an exercise in language nomenclature.

Are there examples of source code?

Yes. There is quite an abondence of source code and libraries of common functions available to the public. The amount of course depends on the popularity of the platform.

Do I have to use a Windows Computer? 

No but it does help. There is software available on other platforms like open source GNU/Linux and BSD but windows still has the major share of the desktop resulting in the majority of the tools, particularly those from the manufacture like software emulation, are windows based. Fortunantly it does not need to be the latest and greatest version of windows nor does your computer hardware have to be top of the line so you can find an old machine and load an older version of windows that you can buy cheap for your development.

Is this going to replace my analog pedals?

NEVER!!!! So saith...

Your Tone God,

Andrew

[MartyMart]

That first guy went to design the Hex-pickups for Shadow, the Blue-Chip (Axon) git-synths, before heading over to AKAI`s sampler adventures...

Yes, I bought an S612 for my studio later - to find out both devices were easier to work with, than the tape-splicing experiences in the 60`s...
(only missing the "natural" fading/phasing, and through-zero-pasteing of the tapes).

That's great Ton, S612 and it's "Quick disk" was my first sampler !! all of 1.3 seconds available  ..
...... man, you had to be "creative" with it   !!

Marty.

[Transmogrifox]

This is very interesting to me that just 2 months ago I got my PIC programmer and started programming uC's...and just about that time, the interest was getting increasingly great in the forum.  It's just about that time that the simplicity of using and programming these things is really catching on for the DIY community.

Things I see uC's useful for immediately is in the realm of digital control for analog circuits.  There is so much circuit overhead in a good analog envelope follower or good LFO module, flip-flop switching for bypass, etc.  I can use the same MCU to do bypass switching, LFO, and envelope follower to take care of all my circuit utility needs, then use the analog signal processing to get the sounds.

Right now i have a digital LFO working in PWM mode on my breadboard.  Pretty neat.  Triangle right now with programmable slope to come (variable between triangle and ramp)

[R.G.]

...and just about that time, the interest was getting increasingly great in the forum.  It's just about that time that the simplicity of using and programming these things is really catching on for the DIY community.

Yeah. I flogged them here for a few years and thought no one was ever going to pick it up.

[Dave_B]

Right now i have a digital LFO working in PWM mode on my breadboard.  Pretty neat.  Triangle right now with programmable slope to come (variable between triangle and ramp)

Someone was attempting that awhile back and couldn't keep the noise out of the signal path.  Have you run into that?  Assuming you're using a chip with ADC's, have you tried putting a pot on one of the ADC channels to vary the rate or slope? 

I wish I had time to do all this stuff.   

[Transmogrifox]

Truth be known, I haven't connected it to my filter yet--just testing the programming side right now.  I expect that sufficient filtering will do the trick.  For an 8-bit LFO the output sample rate is definitely going to fall into the audio frequency range.  Each step on a 5V range will be 5/256 V = 20 mV.   Unfiltered, this is annoyingly audible if fed directly onto the signal path.  I'm using a 512 sample/period triangle wave and varying the sample rate to change the speed.  My longest sample period is about 12 ms, so the frequency is about 83 Hz.

I think a 1rst order low pass cut-off at 8 Hz would make it "not annoying", and a simple 2-pole RC filter w/ cutoff at 20 Hz will pretty well curb it.  I may end up lowering my PWM rate and increasing to the full available 10-bit resolution.