DIY DSP around the corner this time

DavidS · October 27, 2005, 01:08:27 AM

Hey Peter, is this project still in the works? Any news?

I'd love to build one of these!

Primus · February 20, 2006, 02:49:19 PM

Bump! Where is this going?

Peter Snowberg · February 20, 2006, 03:52:17 PM

Right after posting that my life went somewhat to hell. Actually it was a long decline, but that's another story.

Last year my available time went from abundant to about zero overnight while stress went from mild to excruciating at the same time. That really stopped things almost cold and I went a couple months without even posting here. Things are much better now but I still don't have the time I want yet.

There were a couple problems with the wavefront designs. My use of +5V logic next to audio made for too much noise (it was just too small a form factor) and that was solved mostly through layout and a switch to 3.3V digital stuff. The next problem was not so easy... that was the lack of good modulation waveforms. Triangles... easy. Sawtooth... no sweat. Sinusoid anything? Nope. The LFOs are provided by hardware so you get what you get and it isn't what I wanted.

The chips are really cool for some effects like delays, reverbs, and EQ. They're also capable of lots more but not with the flexibility that would cause me to jump for joy for too long. Reverb and EQ were the two top uses so it was a good compromise. The ability to access these chips on a DIY basis was what pushed things in their favor.

This basic design has existed for years before the Wavefront chips were made, so do look at that stuff as the "specification de jour"

. Chips have advanced and the weaknesses of existing parts have been flushed out. The bulk of the DIY DSP stuff is still very much alive, evolving, and consuming 4 to 6 hours a day for me, but it's a bit different now. Details will follow some time in the future, but no comments at this time.

I may still release a Wavefront based design to the DIY world, but it's going to be fairly limited as far as firmware support goes, in fact I've going to leave it all up to somebody else. If it happens, the chip complement would probably drop to one DSP1K and one DRE and would be functionally very similar to the Ms. Parker+ project. I do keep thinking about a digital routing box around a single DSP1K with 8 inputs and 8 outputs as well as a simple programmable DRE based reverb, but other projects are taking priority right now.

Thanks for asking.

Primus · February 20, 2006, 05:03:29 PM

Peter,
Sad to hear about the problems you ran into w/ the wavefront design and life in general. Still, I'm glad to hear that your new project is moving along well and that you have ironed out some of the problems with noise on the digital logic side.

Right now I don't want to press you on your new project, since you have declined to comment on it in two recent threads and I respect your privacy, but I was curious about the amount of labor and parts costs in general for making a do it yourself DSP system like this as opposed to trying to find an evaluation board. Can you give me a ballpark in these two areas? The miss parker project looks hella complicated.

troubledtom · February 20, 2006, 05:23:04 PM

i and dann green{SSSHHHHAND OTHERS} are gonna start a new clubhouse.
ooooooooooohhhhhhhh no, i hear someone coming!
- tom

danngreen · February 21, 2006, 11:11:17 AM

this is very intriguing! often it's the last 10% that takes 90% of the time/effort.
for the waveforms, what about external chips (XR2206) to generate sinewaves, fed into a cheap ADC (even an 8-pin AVR)? I need to spend more time with the datasheets to see if external modulation is possible.....

I'm all ears, keep us posted to progress, and/or if there's anything we can do to help!

Peter Snowberg · February 21, 2006, 11:56:15 AM

Hi Dan.

It's great to see you posting here!

Unfortunately the Wavefront chips are not true DSPs; they're more like MAC cores with a sequencer tied onto the side so they don't even have things like branching. The registers that provide buffer offsets are auto-incremented and not available for program viewing. You can add an FLO to index those pointers, but I don't know if you can get the audio data in channel 1 to affect the index of channel 2 without a serous kludge like presetting an LFO with input data on each cycle and then indexing with that LFO.

In the end I don't think it's a nut worth cracking as there are too many other options in the same price range that give much more performance and flexibility. These chips are great for EQ and delay/reverb applications and that's just where their strength lies. Ask the guy who just picked up the back of the truck what the square root of 4 is and you may not get an answer.

Fun DSP stuff is around the corner and 2006 I think will be the year digital control and DSP finally break into DIY effects.

I know you and Tom will have a part in that process.

Primus, eval boards are a great way to go. I've got three of them from Motorola and they are often worth their weight in gold. This isn't always the case. I did my own boards for the wavefront chips (rather than just buying their boards and figuring out months ahead that it wasn't the direction I wanted) and now I'm counting all that layout time as "practice". Hmmm... maybe they are all worth their weight in gold.

If you've never built a DSP system or high speed digital hardware in the past, I would go the eval route. If you have ample time and budget to spare, have fun with DIY.

troubledtom · February 21, 2006, 08:05:27 PM

Quote from: danngreen on February 21, 2006, 11:11:17 AM
this is very intriguing! often it's the last 10% that takes 90% of the time/effort.
for the waveforms, what about external chips (XR2206) to generate sinewaves, fed into a cheap ADC (even an 8-pin AVR)? I need to spend more time with the datasheets to see if external modulation is possible.....

I'm all ears, keep us posted to progress, and/or if there's anything we can do to help!

that 10% thang you stole from mike both ......... i'm tell'n

your bro,
- tom

danngreen · February 22, 2006, 10:41:42 AM

thanks Peter!

OK I checked out the AL3101 and the reverb chip datasheets. I see what you mean about the simple straight instruction RAM, basically it seems to be set up for effects that have a straightforward algorithm... hmm unless another processor could load instructions in as it reads/responds to the digital out? ayyyy, by then it's best to go with a real DSP.... Which you must have already figured out!

but how's the pitch shifting? A (moderately) accessable pitch shifter with 4 LFOs is enticing!

Peter Snowberg · February 22, 2006, 12:42:15 PM

Let's just say Eventide has nothing to worry about.

The pitch shifting you can do on more capable processors is just too superior to use the 1970s technology available here.

I still do have some plans based on Wavefront chips, but they're more special use devices; one mainly for routing and EQ, and another for reverb.

Have you looked at http://www.axoris.be/ ?

Download the AgALag effects ZIP (actually download everything) and check out the AL3101 code for sine generation. It can be done in math so I was really copping out earlier, but the flexibility just isn't there that I would like for modulation effects.

They have drag and drop effects generation happening. The only downside is that coefficients are computed in the Wavefront chips which takes serious overhead since they're made for in-line processing. I also worry about any PC interface with music gear where you could easily get a big ground loop. Still, very cool stuff!

They have also mentioned working with hardware other than Miss Parker

.

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DIY DSP around the corner this time