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Old 11th April 2006, 02:14 PM   #1
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Question Oversampled TDA1541(a) I2S format?

This may well be a crazy one, which serves only to demonstrate my ignorance of digital formats. But please be patient, particularly if Iím covering old ground Ė It maybe I dont have the vocabulary to search for the right thread.

So Iím trying to figure out my first DAC-from-scratch project. Unfortunately Iím 6000miles away from my soldering iron so this has to stay on the theoretical level.

Iím thinking of using (read want to) the TDA1541(a) with the DF1704 filter and there in lies the rub. Output from the DF1704 is quoted as Ďníbit, MSB first, twos compliment, which I understand rules out using the simultaneous mode of the TDA1541(a)

But what happens if the data from the filter is supplied to the TDA1541(a) in I2S mode? I need two DAC chips I suppose, one for left one for right, but what, if anything, is going to come out of the iout pins?

If this IS just doomed to failure is there an alternative to the SAA7220 that can be set manually? (being able to source it would be a plus too)

Thanks in advance for any advice

Andy
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Old 11th April 2006, 02:57 PM   #2
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I'm also trying to design my first DAC. Good luck to you! Anyway, my question for you is why do you want to use the filter? It kind of defeats the purpose of using the non-OS chip, doesn't it?
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Old 11th April 2006, 03:40 PM   #3
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Default I wondered when that'd come up.

thanks - I have a feeling I'll need all the luck I can get

I want to use the filter because I cant get past the theory of oversampling. vs Non-oversampling.

But I'll probably do both, I'm curious about the Non-OS sound, theoretically it should be a disaster - but I guess its really not.

Anyway the TDA1541 has 3 things going for it for this application

1 Theres LOTS of information about what it likes in terms of installation
2 Its regarded as a good Multibit dac (not Bitstream or Co-phase)
3 I have some.
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Old 11th April 2006, 04:22 PM   #4
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Andrew, I'm also thinking of a design that sounds a little unorthodox, at least, as far as I can tell from these forums. Here it is:

CS8416 (standard S/PDIF receiver) ->
AD1896 (upsample 44.1 to 96) ->
PCM1704 or PCM1794 (bypassing internal DF) ->
I/V conversion

So, I want to use the AD1896 to upsample (and minimize jitter), and then convert to analog, but bypass the digital filtering on the DAC. To me, this seems like a hybrid between OS and non-OS. Whether it is the "best" way, I have no idea, but at least, it should be interesting to find out how it sounds.
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Old 11th April 2006, 05:08 PM   #5
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Default Re: Oversampled TDA1541(a) I2S format?

Quote:
Originally posted by andrew_whitham

<snip>
Iím thinking of using (read want to) the TDA1541(a) with the DF1704 filter and there in lies the rub. Output from the DF1704 is quoted as Ďníbit, MSB first, twos compliment, which I understand rules out using the simultaneous mode of the TDA1541(a)
The pair will work together in simultaneous mode, so long as you convert the two's complement data from the DF1704 into offset binary data.

Quote:

But what happens if the data from the filter is supplied to the TDA1541(a) in I2S mode?
I2S data into an I2S-capable device............

Quote:

I need two DAC chips I suppose, one for left one for right, but what, if anything, is going to come out of the iout pins?
Why ? The I2S bus is a two channel serial bus and the TDA1541A is a 2 channel device.

Quote:

If this IS just doomed to failure is there an alternative to the SAA7220 that can be set manually? (being able to source it would be a plus too)
<snip>
DF1700/SM5813
PMD100
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Old 12th April 2006, 05:32 AM   #6
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Default Thanks,

rfbrw, I'm a little overwhelmed by the conversion from i2s to offset binary, you appear to have to delay the data by one clock cycle. and to be brutal I dont think I kave the knowledge to do that

I expected you'd need 2 DAC chips because the DF1704 outputs bit clock, word clock and Data left / right. But In I2S mode the TDA1541A is accepting bit clock, word clock and Data.

Can you just connect the L/R data streams at the TDA1541A?

Andy
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Old 12th April 2006, 06:34 AM   #7
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The I2S bus can carry 2's comp or offset binary data. Whether the data format is I2S, MSB justified, LSB justified, Sony, Sony/BB or packed is different from whether the number format of the data is 2s comp or offset binary.
The TDA1541A has three modes. I2S with 2's comp data, I2S with offset binary data and simultaneous with offset binary data. In the first two modes 2ch data is input serially and is demultiplexed in the dac, hence the need for only three input pins. In the third mode 2ch data is input simultaneously, requiring separate L and R input pins. The DF1704 will connect to the TDA1541A using the third mode but the data will have to be converted from 2's comp to offset binary. The DF1700/SM5813 and the PMD100 will also connect using the third mode but conversion is unnecessary as the choice of 2's comp or offset binary is pin selectable.
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Old 12th April 2006, 01:11 PM   #8
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Default Easily the most useful thing I learnt today

Thanks rfbrw,

That makes a bit more sense now. so I just spent an (another) hour or so staring at the datasheets and I see the problem - it just wont work! (well not as you say without conversion)

Obviously there's a choice to be made, either I can accept more complexity in the transfer & conversion of data than I want to. Or I need to use different components, either the filter or the DAC.

I think I'll look for one of the PMD100 (or PMD200) chips, the datasheets for those seem to indicate that anything's possible. Hmm.... HDCD requires a 20 bit dac though

Incidentally I cant find a data sheet for the DF1700, even at BB. I take it that means its rare?

Oh well Back to the drawing board - its only electrons.

Thanks again its nice to get some expert guidance.

Andy
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Old 12th April 2006, 01:44 PM   #9
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The DF1700 is a re-badged SM5813, a device long discontinued.
www.datasheetarchive.com have both datasheets.
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Old 13th April 2006, 01:43 PM   #10
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Default Re: Easily the most useful thing I learnt today

Quote:
Originally posted by andrew_whitham
That makes a bit more sense now. so I just spent an (another) hour or so staring at the datasheets and I see the problem - it just wont work!
Donít give up. I think the DF1704/TDA1541 combo would be very interesting. All you have to do is delay the data Ĺ cycle, with respect to BCK, invert the MSB of each sample and generate the LE strobe at the falling edge of WCKO. It could be done with a few flipflops and xor gates.
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