freeDSP - an open source 2-in 4-out digital crossover board

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CharlieLaub

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Joined 2007
audio.claub.net
#1
I want to spread the news about freeDSP (freeDSP | An Open-Source Low-Budget Audio DSP)

This is an effort to develop an open-source hardware platform using the ADAU1701 DSP chip that is similar to the miniDSP 2x4. The main differences include:
  • ability to run at 44.1k, 48k, or 96kHz sampling rate
  • publicly available hardware design (I assume the board's Gerber files will be public)
  • programming done using the SigmaStudio interface instead of the miniDSP GUI
  • lower cost (50 Euro per board)
  • board comes as a DIY kit with thru-hole parts. Any SMD parts will already be soldered to the board.
What you get is a kit that requires assembly, that is less expensive than the equivalent miniDSP offereing, and has greater capabilities than the miniDSP offering (the 2x4). This is not only because it can run the board at a 96kHz sampling rate, but also because SigmaStudio offers a much wider range of DSP processing options compared those available via the miniDSP 2x4 GUI. MiniDSP chose the lower sampling rate and limited DSP architechture for the 2x4 so that it would sit at the low end of their product lineup. With the freeDSP board, all the possibilities that can be supported by the ADAU1701 DSP chip are unlocked through SigmaStudio.

This is a very exciting and superior alternative to the miniDSP 2x4, and I am embracing it 100%.

They are currently accepting names for the first run of these boards at the web site. They need only to reach 20 pcs before they place the first order. If you are at all interested in DSP, this is definitely worth trying.
 

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#4
Some more information on the project - a conference paper from DAFx-14:

http://www.dafx14.fau.de/papers/dafx14_sebastian_merchel_freedsp_a_low_budget_ope.pdf

Elektor Electronics magazine has a quite similar board they sell (the cheapest is a bare PCB with the ADAU1701A soldered for €21.95: http://www.elektor.com/adau1701-universal-audio-dsp-board-130232-72 ). It would be nice if the freeDSP project provided the analog measurements first before attempting to sell the board anyway.

Also if they are goin to manufacture the board (using production house with pick'n place machines) it would be better to select the ADAU1452 as DSP with some inexpensive multichannel DAC like WM8766 (2,26€/piece at Farnell - on the other hand something like PCM1690 would offer a little bit better performance for about €7 price). No ADC would be needed, the chip has got SPDIF input (and output as well): http://www.analog.com/en/audiovideo-products/audio-signal-processors/adau1452/products/product.html

Also you don't really need USBi but that's another story (just find what is common with USBi and EZ-USB FX2 boards available on ebay).
 
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#6
Badge said:
One of the rubs with the Mini DSP for me was the low output voltage for single ended applications. Something like .8 volts. Any idea what the output is for this item?
Click to expand...

I don't think that the freeDSP board does anything drastically different at the D-to-A end. It's probably limited to 0.9Vrms like the miniDSP 2x4.

This is a very common complaint (low output voltage) and I have developed a couple of solutions (coming soon) to address this:

I have developed and refined an analog volume control board that uses a 4-channel VCA for attenuation/gain. I hope to offer this as a board or parts kit. There are a couple of options for interfacing with the board to control the volume, which is done via a 5V control voltage. The user can connect a linear pot of 1k Ohm to the terminals of the control port (5V, control, ground) to control the volume. For remote applications or more sophisticated control, a PIC micro like an Arduino can directly supply voltage or (better) can interface with the board via an external DAC that supplies the 0-5V control voltage. I am working up an Arduino backpack and have some working code for this purpose. Trimpots on the board allow the user to set the volume range. The VCAs can give over 20dB of gain, although I have only tested it up to about 15dB of gain. For instance, 12dB of gain is 4x the output voltage so your 0.9Vrms becomes 3.6Vrms, plenty for any consumer amp. Attenuation of well over 80dB is easily possible. There is also an on-board low-noise power supply - just connect an appropriate transformer to the board.

The other solution is an analog fixed-gain board, also with on-board power supply. I am designing the board now.

(shameless plug): Feel free to contact me if you are interested in any of these.

-Charlie
 
#10
mhelin is so true : it would be MUCH more interesting with a ADAU1452 instead of adau1701. Price could be more expensive but interest would also be bigger... ADAU1452 is much better than all other sigma dsp previous chips including adau1445 ...ADAU 1452 is 2 generations newer with much finer process technology and better SIMD. efficiency is much increased.
With adau1452 I would buy one...
please consider ADAU1452 ... (or ADAU1451)
 
#11
I have been playing with and using the Elektor board for a while. It works just fine.
There is some goofy stuff that I wont populate when I build my next one such as zeners clamping IIC (I will just use a 3.3V arduino for programming), some extra headers, op amp buffers on the aux analog inputs, and so on.

The input caps are too small (0.1 uF resulting in -3dB @ 80 Hz) which is easily fixed by replacing or paralleling 1.0 uF caps.
The output circuit is wierd, but works OK. Quick and dirty measurements show flat response (with the input caps fixed), 5KHz square waves just fine, with a hint of ripplie on top. Distortion < 0.01%.
The output clips with 6V PP applied on the input, output is 2V PP at clipping.
All this with Sigma Studio configured for pass - through.
Noise is not a problem with my 96 dB W/M speakers.

No problems here that cannot be solved with a couple of op amps.
Sigma Studio is pretty nice.
 
#12
Julf said:
Nice that the platform is open source - shame that SigmaStudio seems to only run on Windows.
Click to expand...

My thoughts exactly.

One of my biggest gripes about miniDSP (which I own) is the fact I must use Windows to configure it.

When I saw this "FreeDSP" my first reaction was to get excited, expecting Linux support.

:headbash:

Looks like I might as well stick with miniDSP...

P.S. Why anyone designs software for nerds that only runs on Windows is completely mind-boggling to me.
 
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#16
Carl_Huff said:
The real issue is AD's Sigma Studio. It only runs on Windows boxes. The FreeDSP team has no control nor influence over that.
Click to expand...

Mostly correct. However, AD does offer "SigmaStudio Network Utility for Linux". SigmaStudio Network Utility for Linux [Analog Devices Wiki]

This allows a Linux box with DSP(s) connected to run a network service (sigma_tcp) which can be controlled by a remote Windows computer running SigmaStudio.

What this tells me is that the drivers for Linux are already there and functioning - the Linux box can communicate and "program" these AD DSPs. The only thing missing is a native GUI for Linux. How hard could that be?

I am just used to associating the terms "free" and "open" with "free" and "open" operating systems. To have a project named "freeDSP" which relies 100% on a non-free operating system seems contradictory and ironic.
 
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#20
I'm going to see if I can get SigmaStudio to run in WINE...

Perhaps WINE will cause some sort of issue since SigmaStudio will assume it is running in Windows and not use the right drivers for the DSP, however one way around this might be to run the native linux sigma_tcp service listening on 127.0.0.1 and then run SigmaStudio in WINE and use the "TCPIPADAU17xx" module to connect to localhost (127.0.0.1).

Worth a try! 🙂

Too bad I am at work, where I am forced to use a Windows machine. 🙁
 
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