freeDSP - an open source 2-in 4-out digital crossover board - diyAudio
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Old 6th November 2014, 05:10 PM   #1
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Default freeDSP - an open source 2-in 4-out digital crossover board

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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Old 6th November 2014, 07:34 PM   #2
Julf is offline Julf  Europe
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Nice that the platform is open source - shame that SigmaStudio seems to only run on Windows.
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Old 6th November 2014, 07:59 PM   #3
Badge is offline Badge  United States
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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?
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Old 6th November 2014, 08:00 PM   #4
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Some more information on the project - a conference paper from DAFx-14:

Elektor Electronics magazine has a quite similar board they sell (the cheapest is a bare PCB with the ADAU1701A soldered for €21.95: ). 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):

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).

Last edited by mhelin; 6th November 2014 at 08:21 PM.
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Old 6th November 2014, 08:12 PM   #5
rdf is offline rdf  Canada
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Can't tell from the schematics, will the board permit routing a digital out to one of the headers?
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Old 6th November 2014, 08:20 PM   #6
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Originally Posted by Badge View Post
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?
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.

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Old 7th November 2014, 08:54 PM   #7
Boden is online now Boden  Netherlands
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Very interesting. It might be useful though to combine the efforts done here with the ones member Basreflex is currently undertaking in the very similar nanoDSP thread on DIYAudio.

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Old 15th November 2014, 10:36 PM   #8
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Any updates here?
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Old 16th November 2014, 12:00 AM   #9
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I suggest that you inquire at the freeDSP site... I'm just the messenger and the designers don't frequent this forum.
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Old 18th November 2014, 10:44 PM   #10
ejaouen is offline ejaouen  France
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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)
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