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Old 12th January 2011, 01:10 AM   #161
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I'd be far more interested in a USB in/I2S in/I2S out crossover board than a 8 channel USB 'sound card'. There are already plenty of multichannel sound cards available. Of course if it can do both that's the best of both worlds.

The world needs more DIY aimed DSP crossover solutions.....

If this board has more 'grunt' than the miniDSP boards it would be very popular.
 
Old 12th January 2011, 01:37 AM   #162
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I would have thought that the multichannel support would be handled entirely with the USB2 standard audio driver.

You might need a micro to configure the Xmos chip so that it is flagged as 8 channel capable or something though. I'd have thought, however, that besides software, the only added hardware complexity, in going from 2 channel to 8 channel, would be the addition of 3 more I2S data lines on the header. Ditto for a data input. I'd want 8 channels for going surround sound eventually.

RE DSP, the sigmaDSP chip that the minidsp is built around is fully capable of handling 24bit/192 khz. What happens though is that the number of computations it can process per time frame decreases proportionally as the sample frequency increases. So if you're pushing the limits with a 48khz system, you'd need something 4x more powerful to handle 192.

The minidsp chip uses one of the lower power sigma chips, the advantage is that it comes with A/D D/A conversion built in, so makes for a very affordable 2 way stereo DSP. Although in absolute terms the A/D D/A converters are very low quality as far as top notch converters go. But then the basic minidps board only costs $99, so you can't expect ESS sabre or PCM1792/4 quality converters.

I've been experimenting with the daddy of the chips, the ADAU1442, in analogue devices purpose built software allowing you to program the DSP without any coding knowledge. Currently I am using about 1/3 its processing power running 24/192 over 4 stereo channels. As you can see in the attached image this uses quite a lot of xover building blocks too so there's plenty of power left available for other things.

I am currently designing a PCB for the ADAU1442 and intend on seeing just what it's like. If the TPA USB interface ends up being what I want I'll probably be buying one to feed into the DSP board.

It might be worth TPA considering such a board themselves. I think there'd probably be a decent amount of interest in a similar ADAU1442 DSP board, with I2S inputs and outputs. Just another board to add to the mix

In the interest of quality though, the ADAU1442 has an extremely flexible way of handling the various clocks, so I'd imagine very low jitter should still be on the cards, if it's configured right. That however I will try and find out for myself.

fb, I sincerely doubt that the Xmos chip is more capable then the minidsp.
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Old 12th January 2011, 03:16 AM   #163
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Sigmastudio certainly looks great. Is it possible to use it with 'retail' boards, or just the eval boards?

Having recently ordered 3x Opus, I'm in the market for a I2S based DSP.

miniDSP isn't powerful enough for the price (I'd need 2 boards for stereo 3 way), and this project is progressing slowly due to the firmware development process, something the SigmaDSP platform seems to make obsolete.
 
Old 12th January 2011, 04:02 AM   #164
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Quote:
Originally Posted by 5th element View Post
I would have thought that the multichannel support would be handled entirely with the USB2 standard audio driver.

You might need a micro to configure the Xmos chip so that it is flagged as 8 channel capable or something though.
Yep, I am investigating supporting 8 channel right off the bat. But the problem is that with the L1 chip there are (surprisingly) very few open 1bit IOs.

I am seeing what I can do though.
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Old 12th January 2011, 10:48 AM   #165
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Originally Posted by lauret View Post
Wouldn't that be possible using software (and hoping on multi-channel outputs for this module)? Or are you referring to a seperate hardware DSP?
I would think hardware a better approach. The model I had in mind, and I've only recently started researching this, is to USB a stereo stream from the PC (or SPDIF from a transport) and then use a DSP to run the crossover algorithms (a la miniDSP). This would output separate I2S or SPDIF streams to individual high quality dacs, creating a fully separate stereo pair for above and below the cross over point.

Of course this gets expensive for a 3 way speaker system but isn't too bad for a two way speaker (such as mine).
 
Old 12th January 2011, 10:58 AM   #166
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Originally Posted by 5th element View Post
I would have thought that the multichannel support would be handled entirely with the USB2 standard audio driver.

You might need a micro to configure the Xmos chip so that it is flagged as 8 channel capable or something though. I'd have thought, however, that besides software, the only added hardware complexity, in going from 2 channel to 8 channel, would be the addition of 3 more I2S data lines on the header. Ditto for a data input. I'd want 8 channels for going surround sound eventually.

RE DSP, the sigmaDSP chip that the minidsp is built around is fully capable of handling 24bit/192 khz. What happens though is that the number of computations it can process per time frame decreases proportionally as the sample frequency increases. So if you're pushing the limits with a 48khz system, you'd need something 4x more powerful to handle 192.

The minidsp chip uses one of the lower power sigma chips, the advantage is that it comes with A/D D/A conversion built in, so makes for a very affordable 2 way stereo DSP. Although in absolute terms the A/D D/A converters are very low quality as far as top notch converters go. But then the basic minidps board only costs $99, so you can't expect ESS sabre or PCM1792/4 quality converters.

I've been experimenting with the daddy of the chips, the ADAU1442, in analogue devices purpose built software allowing you to program the DSP without any coding knowledge. Currently I am using about 1/3 its processing power running 24/192 over 4 stereo channels. As you can see in the attached image this uses quite a lot of xover building blocks too so there's plenty of power left available for other things.

I am currently designing a PCB for the ADAU1442 and intend on seeing just what it's like. If the TPA USB interface ends up being what I want I'll probably be buying one to feed into the DSP board.

It might be worth TPA considering such a board themselves. I think there'd probably be a decent amount of interest in a similar ADAU1442 DSP board, with I2S inputs and outputs. Just another board to add to the mix

In the interest of quality though, the ADAU1442 has an extremely flexible way of handling the various clocks, so I'd imagine very low jitter should still be on the cards, if it's configured right. That however I will try and find out for myself.

fb, I sincerely doubt that the Xmos chip is more capable then the minidsp.
5th E

An excellent and informative post - thanks. It echoes my thoughts regarding the current miniDSP offering. I am not interested in doing digital analogue conversion at the DSP (unless it's a Sabre32 dac!) just want to get the crossover implemented in the digital domain and use downstream dacs to handle the conversion.

Mark
 
Old 12th January 2011, 11:18 AM   #167
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I agree, that would be such a great thing to be able to do. I've been thinking along these lines for sometime but haven't seen a solution that really cuts the mustard yet. Just think of what you could do with a really high quality USB Transport - USB DSP crossover that outputs I2S - DACs - Poweramps. Not sure where would be optimum point to incorporate volume control.
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Old 12th January 2011, 12:06 PM   #168
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Originally Posted by simon dart View Post
I agree, that would be such a great thing to be able to do. I've been thinking along these lines for sometime but haven't seen a solution that really cuts the mustard yet. Just think of what you could do with a really high quality USB Transport - USB DSP crossover that outputs I2S - DACs - Poweramps. Not sure where would be optimum point to incorporate volume control.
Dual/triple-ganged Volumite pots at the DAC or incorporate into the DSP - miniDSP allows that.

I want to keep a balanced signal out from the DACs as my Hypex amps sound noticeably better fed a balanced diet and balanced preamps are more complex and costly than they're worth most of the time.

Mark
 
Old 12th January 2011, 02:36 PM   #169
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Sigmastudio certainly looks great. Is it possible to use it with 'retail' boards, or just the eval boards?
It depends on how handy you are with the DIY and how the retail implementation has been designed.

AD manufacture a board specifically for interfacing the DSP evaluation modules with sigmastudio. The board is basically a USB to I2C/SPI converter. If you could modify the retail unit so that you could get access to the control pins, then I am sure you could directly control the chip via ADs USB-I2C board.

SigmaStudio is free on request from AD, but they didn't want to release the firmware programmed into the USB to I2C converter. Naturally this means I'd have to buy theirs, if I want to guarantee success. It isn't outrageously expensive @ $99. Note that AD don't allow a company to provide SigmaStudio along with their product, the company would have to write their own software.

Sigmastudio will output the code that's actually used to program the DSP chip, in both hex and binary. So I am sure it wouldn't be too much trouble for someone competent at micro controller programming to write their own program that could upload the hex file to the DSP chip. Currently I know zero about programming, but I have a project coming up where I intend to learn!

The brilliant/interesting thing about the sigmadsp chips is that they aren't hugely expensive. I think the ADAU1442 will cost me something like 15 each? And to make a board with I2S inputs/outputs would require nothing more then the DSP chip, a few caps and resistors, a crystal, a voltage regulator, a E2PROM and the headers. So it's cheap and small seems perfect for TPA board

If you're intending on buying a retail product, to use with ADs USB-I2C module I will say a couple of things.

The 1442 can operate either with a micro controller sending it the code, or on boot it can grab the code from some E2PROM memory. The E2PROM memory isn't built into the chip and has to be provided separately, but once in place it will allow the chip to self boot, without the need for a micro controller. (Instead of the micro sending the 1442 the code on boot up, the 1442 grabs the same code from the memory instead. You have to select what boot mode you want to use by altering the state of one of the 1442s pins.)

You would have to make sure that the retail product is configured in the correct way, or that you could modify it to be, otherwise it'd be a pain to use. Do you know of any retail products that work around the sigma chips besides the minidsp?
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Old 12th January 2011, 02:41 PM   #170
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Originally Posted by Goto View Post
I would think hardware a better approach. The model I had in mind, and I've only recently started researching this, is to USB a stereo stream from the PC (or SPDIF from a transport) and then use a DSP to run the crossover algorithms (a la miniDSP). This would output separate I2S or SPDIF streams to individual high quality dacs, creating a fully separate stereo pair for above and below the cross over point.

Of course this gets expensive for a 3 way speaker system but isn't too bad for a two way speaker (such as mine).
That's what I've been looking for a long time.

Exactly, my aim is to find a surround decoder that outputs NOT 6 analog outputs, but 6 spdif outputs (or even I2S). That way I can use 3 external high quality dacs.
Nowbody looks for this solution, but it doesn't seem an strange thing. Are any of you using a Home cinema sorround at home? Are you using the crappy integrated dacs of the receiver?

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