XO3: The 1/2/3-way Active Crossover/filter PCB. Design suggestions welcome! - Page 4 - diyAudio
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Old 30th January 2011, 09:39 AM   #31
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As long as there are 24-bit DACs on the outputs, the dither shouldn't make difference - the lower bits will be lost in DAC's noise floor anyway. At least i hope so
16bit DAC's performance will suffer from the dither tho... Still, most of 16bit DACs require upsampling DF on their input - maybe their DF will do the dither job...
Ahh, that means i couldn't use TDA1541 in NOS for midrange output

This device uses the TAS:
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Old 30th January 2011, 10:13 AM   #32
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Seems a little odd to me that a $4k box would use a $5 DSP. They've paid a fair bit of attention to various implementation details but not to dither. Many years back, when I was working amongst a team of pro audio guys designing a digital console, they were concerned about dither and devoted a significant area of silicon in their custom processor to getting it right. I doubt one feedback shift register really cuts the mustard. For a start, TPDF dither (the kind that doesn't introduce noise modulation) is created by summing together two noise sources.

The notion that the dither is beneath the noise floor might have some merit, but I'd not want to bank on it.

I guess I'm just conservative in my engineering instincts, I wouldn't feel comfortable investing development effort into something based on just hoping it will sound fine
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Old 30th January 2011, 11:51 AM   #33
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Yes, they use the TAS3108:
http://www.groundsound.com/dcn24.php

The $4k price tag is made from nice case, ADCs, DACs,PSUs, volume reg, propertiary software, pro assembly and "High-End" thing...

Well, one of the I2S inputs could be used as dithering noise input And then mixed with a processed signal...
L/R input and bitclock will be sourced from the WM8804, and data signal could be generated externally and then processed in the DSP to become 1-bit "noise"...
The problem as i see it is to make this noise uncorrelated with audio signal and other noise sources - we are going "analog" on this input, and proper function should be applied to normalize the noise source...

I've choose this chip just because it is easy to implement, cheap, and wouldn't require much development efforts/time/costs. In addition, it's clocking scheme seems nice and flexible (could work as slave for the DACs, could take it's clock from the I2S input, could be master for all other components...).
WM8804+TAS+EEPROM+4xWM8804 - and viola, you've got the cheapest DSP board ever

By the way, it could do FIR too - going down to ~400Hz of filtration at 44.1kHz.
Too bad it doesn't have sample rate converter inside - then i could use it as DF for the TDA1541/PCM63/58/etc. I could use some ASRC on it's input, and then do all the filtration at 4xFs rate... Seems pretty flexible for it's 5$. No analog inputs - doing ADC is always wrong.

Still, the project is "for fun", fully opensource e.t.c.

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Old 30th January 2011, 12:04 PM   #34
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Quote:
Originally Posted by s3tup View Post
Well, one of the I2S inputs could be used as dithering noise input And then mixed with a processed signal...
Yes Good thinking!

Quote:
Too bad it doesn't have sample rate converter inside - then i could use it as DF for the TDA1541/PCM63/58/etc. I could use some ASRC on it's input, and then do all the filtration at 4xFs rate... Seems pretty flexible for it's 5$.
Its about twice the price but given that it includes 8 channels of ASRC, this one might be better if you're really hankering after SRC:

Analog Devices ADAU1445
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Old 30th January 2011, 12:11 PM   #35
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The SigmaStudio seemed to me less DIY-friendly, so i've discaded AD DSPs from the wishlist Practically AD's requirement to buy a dev board to get the studio...
I'm not a fan of ASRCs unless they are synchronus and stable.
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Old 30th January 2011, 12:24 PM   #36
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I'm planning to do something similar to your idea, but neither of those chips appeals to me owing to proprietary lock-in. So I'm eagerly awaiting the LPC4000 series from NXP to kick start my ideas. In the meantime I do have an LPC1768 board to get me some way along the learning curve with the tools.
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Old 30th January 2011, 12:39 PM   #37
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Wow, LPC's are nice - ethernet/usb stack + real MCU + DSP in single chip - looks like pretty sophisticated network/usb transport/crossover/room EQ could be made.
Lots of coding tho... Not that i'm afraid of coding, but i hate C language

Another interesting option for DSP xover/room correction is a plain FPGA with full-sized FIRs.
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Old 30th January 2011, 12:52 PM   #38
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Wow, LPC's are nice - ethernet/usb stack + real MCU + DSP in single chip - looks like pretty sophisticated network/usb transport/crossover/room EQ could be made.
Yes, and remarkably low power too. Oh, you forgot the LCD

Quote:
Lots of coding tho... Not that i'm afraid of coding, but i hate C language
Me too, so there's only one solution - Thumb-2 assembler Assembly coding is so much more fun even though it takes longer. If I used C I'd be wanting to find out why it ran so slowly anyway, so why not miss out that step?

Quote:
Another interesting option for DSP xover/room correction is a plain FPGA with full-sized FIRs.
Yes, pretty much subject to proprietary lock-in there too. So ARM's the way to go for me.
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Old 30th January 2011, 12:58 PM   #39
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You're not going to write the TCP/IP stack in ASM, aint you?
Inline is the way to go, leaving the "boring" parts to C and "fun" to fingers...
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Old 30th January 2011, 01:03 PM   #40
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Wasn't planning on doing anything with the ethernet in the first instance, no. My idea is to start out as a battery powered FLAC SD card player with built-in XO for two-way active speakers. Then grow it incrementally from there.
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