DIY DSP Engine

[Paul Ebert]

I'd like to educate myself on DSP by making a DIY digital equalizer and loudspeaker crossover. So far, in my research into getting started, I've run across the TI TMDSDSK6713 development board (see http://focus.ti.com/docs/toolsw/fold...dsdsk6713.html) as a good and affordable DSP hardware platform I've also found a board that plugs into the TI board (see http://www.mds.com/Products/product.asp?prod=ADK) that provides for audio input and output.

Is anyone else doing this sort of thing? Does anyone have other suggestions for hardware? Lastly, what would it take to build something like the MDS board? I have an BSEE degree, but I've been a software guy for the last 20 years. What does it take to do DIY board design and assembly these days?

The MDS product costs around $1000, so building something would have to be cheaper enough to make it worth the while.

Thanks.

Paul Ebert

[Mark25]

There was a guy doing just that sort of thing at the Dutch DIY audio day, sorry i can't remeber his name. He had got analogue and digital active X-overs in the same box. He could switch between the two from his pc/listening seat and alter the digi parameters from there too. Driving some pretty high class drivers from it too, although, the digi side of things wasn't fully operational yet. Very impressive!
Mark

[mhelin]

I'm going to use Alesis (Wavefront) 1 KS DSP with Alesis DAC's and Crystal receiver. Also a microcontroller is needed to upload the firmware (size is just 1024 x 3 bytes) - maybe you could use the parallel or even serial port (control lines) of PC for the job. I wish someone could desing the PCB (for DSP, S/PDIF receiver and DAC's, with a header for DSP serial port to wire to external MCU card / parallel port etc.) and arrange a group order for them. These are really inexpensive chips and easy to use. The 1 KS (1 KM, the parallel interface version) DSP has 1024 instructions / sample to process, so it's possible to implement a decent FIR xover with them. For EQ like BSC (baffle step compensation) an analog circuit suits much better (to conserve the dynamic ration of DAC's).

Alesis Semiconductors

[Paul Ebert]

Let me see if I understand your point. If digital EQ is applied, say to provide some bass boost or bsc, then, for those frequencies that are boosted at least, the DAC is 'biased' toward higher bits. This then reduces the dynamic range for those frequencies. Is that what you are saying?

Seems like a good point that hadn't occured to me before. I'll have to think about that some. Probably wouldn't stop me from using digital EQ, though.

Paul Ebert

[mhelin]

Yes, but of course you could apply the BSC just to the lowpass channels so you loose some (6 dB with full BSC, that's one bit of resolution) dynamic range from the f-6 point (like @450 Hz with 25 cm wide baffle) up till crossover frequency. Sadly that's the area where the human ear is most sensitive. Anyway, as a hybrid filter you could implement the analog BSC and a digital allpass with opposite phase response to keep the phase as linear as possible (if you think the phase linearity is important). The AL1201 DAC's have 107 dB SNR so 101 dB is still pretty good, still above 16-bit performance (shouldn't propably matter).

[DSP_Geek]

Originally posted by mhelin
I'm going to use Alesis (Wavefront) 1 KS DSP with Alesis DAC's and Crystal receiver. Also a microcontroller is needed to upload the firmware (size is just 1024 x 3 bytes) - maybe you could use the parallel or even serial port (control lines) of PC for the job. I wish someone could desing the PCB (for DSP, S/PDIF receiver and DAC's, with a header for DSP serial port to wire to external MCU card / parallel port etc.) and arrange a group order for them. These are really inexpensive chips and easy to use. The 1 KS (1 KM, the parallel interface version) DSP has 1024 instructions / sample to process, so it's possible to implement a decent FIR xover with them. For EQ like BSC (baffle step compensation) an analog circuit suits much better (to conserve the dynamic ration of DAC's).

Alesis Semiconductors

I'd recommend the TI c671x series. The chip is somewhat more expensive at $22 ($5 for Alesis), but the DSP starter kits are not far off (TI=$395 vs Alesis=$250). TI wins on CPU power - they claim from 600 to 1350 MFLOPS vs 49 MIPS for the Alesis, so for a 60 % increase in prototype system cost you get at least 10x performance. The TI chip, by the way, does 32 bit floating point as well as 24 bit integer. 32 bit integer is also available, but I haven't checked to see whether that involves an efficiency hit.

http://focus.ti.com/docs/toolsw/fold...320006711.html
http://focus.ti.com/docs/toolsw/fold...dsdsk6713.html


Francois.

[DSP_Geek]

I forgot: I *like* mhelin's idea of a daughtercard design & group buy. Momentum Data Systems wants a grand for their 4-in 8-out card; that's a bit pricy for something hanging off a $400 dev board. I'd be all over putting together a DIY board but my analog days are way behind me. Hmmm. Now how do we get some of that fancy mixed-signal design talent on the other boards to show up here?


Cheers,
Francois.

[tiroth]

DIYing the BGA package is a bit...impossible.

What we could also really use is some software. There are a lot of people that could assemble the working hardware, but a bare handful who have the skill to write the software.

[DSP_Geek]

Originally posted by tiroth
DIYing the BGA package is a bit...impossible.

What we could also really use is some software. There are a lot of people that could assemble the working hardware, but a bare handful who have the skill to write the software.

No no no no, not the DSP in BGA. We can buy the DSKs for $400, I'm happy with that. I was talking about DIYing DACs hanging off the daughterboard connector. I have enough mixed-signal chops to make vague recommendations but the heavy lifting, well, I'd be really pleased to admire someone experienced.

And I've been doing DSP code for a while now, so:

WILL PROGRAM FILTERS FOR FOOD, er, DACS.


Francois.

[Paul Ebert]

I'd be quite satisfied with the TI DSK as well. The price seems fine for the hardware and development software provided. What I'd like to see on the daughterboard would be two channels of high quality ADC, six or eight high quality DACs and some sort of high powered (24/96 would be nice) digital I/O as well.

BTW, what is JTAG (can you tell I'm a DSP newbie)?

I have no DSP software experience, but loads of rather intense embedded software experience (medical devices). I'm looking forward to writing the software, if I can get the hardware together.

I'm fairly new to this board. Where do those mixed signal gurus hang out?

Paul