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Old 13th January 2007, 09:15 AM   #1
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Default Using 20 bit data with a pair of old 16 Bit DAC

Hello All .

Is it possible to let a pair of TDA1543 play the 20 bit data from a DVD player . Can somebody help with a schematic ?

Thanks
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Old 13th January 2007, 03:59 PM   #2
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So long as the data is in the right format for the TDA1543, you do not have to do anything. The 4 LSB's will be ignored.
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Old 13th January 2007, 04:28 PM   #3
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..and cause an ugly truncation distortion due to undithered requantization
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Old 13th January 2007, 04:51 PM   #4
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Quote:
Originally posted by Glassman
..and cause an ugly truncation distortion due to undithered requantization
INFACT The distorsion goes away as the recording level goes down

The idea is to split the 20 bit data word in 2 words of say 10 bit , one for each 16 bit dac ....

but I need some help to realize it in practice ....


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Old 13th January 2007, 05:02 PM   #5
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Quote:
Originally posted by Glassman
..and cause an ugly truncation distortion due to undithered requantization
Thats only 4 bits lopped off. There are those that send 24/96 data to the TDA1543 and swear it is the greatest thing ever.
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Old 13th January 2007, 05:10 PM   #6
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doesn't matter at all how many bits it is, the damage is exactly the same whether you start with 20, 24 or even 32 bits.. luckily this gentleman does not attempt anything of this sort..

btw. good luck calibrating the two DACs to within half the 20th bit level..
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Old 13th January 2007, 05:19 PM   #7
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Digital filters often perform straight truncation. There is no way the the sonic effects of a 2 bit truncation are as bad as a 4 or 8 bit truncation.
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Old 13th January 2007, 05:24 PM   #8
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Why not just get a modern 24 bit pcm dac like the Ti PCM1794 or PCM1798 or the Analog Devices 24 bit AD1852 sigma delta dac?

The results are liable to be way better with any one of these than with two ancient 16 bit dacs used with a 20 bit word.

The point about calibrating the two is also valid, and I think this will cause a huge linearity issue..

The two chips are unlikely to have identical drift so it is unlikely that the two will hold their calibration over time and temperature either. Such things are regularly done in dc ATE applications, but are subject to frequent calibration and checking. AC I think would open a whole new can of worms.

Edit: fix typo
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Old 13th January 2007, 05:39 PM   #9
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Quote:
Originally posted by rfbrw
Digital filters often perform straight truncation. There is no way the the sonic effects of a 2 bit truncation are as bad as a 4 or 8 bit truncation.
Yes of course , that is true if I can use a 24 bit dac and start truncating bits to hear the effects .
The problem is that 18, 20 or 24 ( or more ) bits into a 16 bit dac simply doesn work properly .

Quote:
Originally posted by kevinkr
Why not just get a modern 24 bit pcm dac like the Ti PCM1794 or PCM1798 or the Analog Devices 24 bit AD1852 sigma delta dac?


Edit: fix typo
Yes Ok thats right . But I am getting rid of the AK 4365 (20 bit sigma/ delta) for a multibit DAC for personal taste reasons . I should try to find an old 20bit AD1862 , but I think it comes down to space matters inside the little DVD player .

EDIT :

.... more over ( and correcting myself ) the dvd player outputs I2S in Philips format , while both PCM and AD think want Sony format . SO ...
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Old 13th January 2007, 06:07 PM   #10
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Quote:
Originally posted by rfbrw
Digital filters often perform straight truncation. There is no way the the sonic effects of a 2 bit truncation are as bad as a 4 or 8 bit truncation.
such filters should be prosecuted by the law.. and yes, 2, 4 or 8 bits of truncation - no difference, it only depends on the level at which the truncation happens, not on the number of bits you're loosing..
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