Digital (DSP) filter

[magnus]

Hi,

I've been wanting to build a digital filter for some time. Basically I want a simple board that just accepts S/PDIF, puts it through a DSP with your own algorithms and then outputs an S/PDIF signal again.

Sounds so simple but I can't find info anywhere!

Even if I do 24/96 it shouldn't require a very fast DSP. They all seem to be 1000 MIPS these days. I'm pretty sure I want to do floating point as well. Seems to be the simplest way to get a good algorithm.

So does anyone have a layout or some info or maybe someone already did this?

TIA,
Magnus

 

[dwk123]

I can't help you too much on the hardware side in terms of current offerings. Motorola used to make EVM boards that would be perfect for what you want - I have 56007 and 56362 versions - they have spdif and analog ins/outs. They weren't cheap though - $400-500 if I remember correctly. somewhat limited in their overall processing power, though, if you ever want to do FIR filtering. More than adequate for IIR/biquad stuff, though.

Many 'purists' will cringe at the suggestion, but you should think about simply using a PC with a good spdif in/out soundcard. Using ASIO under windows or Jack under Linux you can get relatively low latency (more than good enough for A/V sync), and you get to use standard C/C++ dev tools and libraries.

I'm a big fan of the PC based approach, after having played with the DSP hardware boards. Since I'm not a DSP hardware expert, I spent all my time learning the chips/dev tools, and little on actual signal processing work. With something like Jack under Linux (what I'm using now), you get to focus entirely on the signal processing aspects inside a really simple callback framework.

 

[ebrewste]

You might look at the TI TAS300x or TAS 3103 (newer). I am using a TAS3002 in a project now. It's good for 6 biquads filters per channel.

 

[blu_line]

There is another cheap DSP also discussed in this forum before.
ohh, sh*t , why cant i remember the name !

I will come up with it !

And what about one of those PC18Fxxx things ???


grtz

Simon

 

[blu_line]

mail me

I have tried to mail you.
It seems you've disabled this function !
mail me instead.


grtz

Simon

 

[jackinnj]

Sharc boards for sale

you can buy the Analog Devices Sharc DSP EV kit cheaply on EBay -- these are the boards which are showing up:
http://www.analog.com/Analog_Root/productPage/productHome/0,,21061%2DHARDWARE,00.html

ADI also has an entire textbook on DSP on their website. They make convultion understandable. Even Zipped its a big file, however, and you might want to download it chapter by chapter.

 

[blu_line]

phew, that took a while to find

http://www.alesis-semi.com/products.htm


great stuff


grtz

Simon

 

[magnus]

Thanks for the info everyone.

I guess this is a tough little problem to solve (cheaply) with a DSP. I definately want to go FIR and maybe 50 coefs. So that requires some computing power.

The PC path is always there but it doesn't really fit in with the high end stuff. So I'm reluctant.

I'll look around some more and see what I find.

Magnus

 

[dwk123]

Thanks for the info everyone.

I guess this is a tough little problem to solve (cheaply) with a DSP. I definately want to go FIR and maybe 50 coefs. So that requires some computing power.

50 taps is nothing - any dsp will handle this no problem at 44 or 48 - the Motorola 56362 I mentioned previously can do 500-800 at 44.1 for comparison. You may want to think about your requirements, though, since a 50 tap fir may not really be what you want - you could do acceptable brickwall filters for example, but it wouldn't be much use for eq.

The PC path is always there but it doesn't really fit in with the high end stuff. So I'm reluctant.

I'll look around some more and see what I find.

Magnus

Not sure what you mean here - with spdif in/out, the quality will be uniform with any of these approaches. Since the clocks will be slaved from your transport, even jitter should be the same. The differences will be in form factor (small, quiet dsp board vs big noisy pc), and in programming environment.

 

[magnus]

50 taps is nothing - any dsp will handle this no problem at 44 or 48 - the Motorola 56362 I mentioned previously can do 500-800 at 44.1 for comparison. You may want to think about your requirements, though, since a 50 tap fir may not really be what you want - you could do acceptable brickwall filters for example, but it wouldn't be much use for eq.

You're right. I do need to find out exactly what I need in terms of performance. 500-800 taps sounds like more than enough. I checked the Mot website and that eval board with the DSP daughterboard looks good. But pretty expensive I bet.

Not sure what you mean here - with spdif in/out, the quality will be uniform with any of these approaches. Since the clocks will be slaved from your transport, even jitter should be the same. The differences will be in form factor (small, quiet dsp board vs big noisy pc), and in programming environment. [/B]

Quality will be unifom, yes. But the big PC case doesn't look so nice compared with the Krell stuff. I want a slick solution.

After looking some more I came up with the Linux/ARM route. Maybe that could be something? Possibly cheaper than the eval boards and loads more software for displays, keypads and whatnot.

/Magnus

 

[Mark Hathaway]

the pc path isn't so bad

I'm using a St audio dm3 digital i/o box (4 aes/ebu, spdif ins and the same number and style outs) www.staudio.com

Got the computer out of my listening room, running a few feet of aes/ebu

Software is Sounds Logical's Wavewarp package. http://www.soundslogical.com/

Generating my own filter coefficients in FIR Filter Design http://www.dspguru.com/sw/tools/filtdsn2.htm while I'm waiting for a compatable version of Matlab (most current version is not compatable)


I'm using 4 ad1896 eval boards running off batteries for external dacs.

So I can quite happily do a 3 way speaker and a sub, with room eq thrown in.

With a 733Mhz not much (ok none) real time work is possible, but I can quite happily pre process and then sequence from Cool Edit Pro 2


The FIRdesign application isn't that user friendly or option packed, but I can manage 1000th order.


Xover points are 60hz, 200hz and 5000hz.


Now just wish I could manage the same with a stand alone DSP box. I've no real dsp/programming knowledge, speaker/room design is my field.


Mark Hathaway

 

[hifiZen]

Hmm... well, I've had a pretty much complete hi-fi DSP design ready for almost two years now... based on Analog Devices ADSP-21065L. Tons of processing power and I2S in/out ports too! But, I've just never gotten around to finishing the layout and having the boards made... I bought all the parts ($$$) for two prototype boards. So many other projects to work on...

Gradually, I'm getting closer, though. So, with some prodding, I may get around to putting it together after all. Actually, the amount of work is growing, since I'm getting better at design over time, and new parts are coming out... so the list of things I'd like to change in the design keeps getting longer!

 

[magnus]

@hifizen:

Just let me know when you have that board ready! Sounds like exactly what I need.

I've looked at the Behringer UC 8024 too but of course you can't program it yourself. It's probably hard to beat for €219 though...

Magnus