SM5816A ( DSD to PCM ) - diyAudio
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Old 13th December 2002, 11:19 PM   #1
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Default SM5816A ( DSD to PCM )

I have some sample ( and the evaluation board ) of this interesting IC for convert to PCM the DSD stream ( so i can have a digital interface from any source for the my project of multichannells digital room equalization processor ).

The problem is that the pcm outputs of this IC are six discrete pcm signals at 2fs ( 88 Khz. ) 32 bit and ( or ) six discrete pcm signals at 8fs ( 352 Khz. ) 24 or 32 bit of resolution.

Have anyone some idea for convert/adapt these exotic signals for be used with normal SRC ( AD1896 for example ) ?

Thanks and regards

Marco
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Old 14th December 2002, 01:32 AM   #2
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The SM5816AF's 8fs interface has six discrete mono data outputs, one for each channel (plus a left and right subwoofer output).

The 2fs interface has only three non-exotic stereo data outputs: one for front left / front right, one for surround left surround right, and one for center / subwoofer.

These 2fs outputs will interface directly to the AD1896 inputs.
(I'd suggest using the 'standard' IIS mode).

You'll need three AD1896s configured in phase-matching mode (so they'll all have the same group delay): One configured as a ratio master, the other two as ratio slaves.

I've got both of these parts and am planning to set up a circuit along the lines of what you're discribing. At this point it looks like it will be at least a couple of months before I can start working on this. I think it'll be a great way to listen to surround SACD's.

Brian.
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Old 14th December 2002, 01:51 PM   #3
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Brian,

Thanks for your reply.

I have read with more attention the document of the evaluation board ; it is right that the 2FS are 3 PCM outputs ( for the six channells ) and that is selectable in IIS format but only at 32 bit ( the other format for 2fs is MSB-first left justified and always at 32 bit ).

Is this 88 Khz. IIS 32 bit pcm format ok for the AD1896(5) ?

The 24 bit are only for the six 8fs discrete channells :

8fs MSB-first left-justified 32 bit pcm format or 8fs MSB-right-justified 24 bit pcm format.

Regards
Marco
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Old 14th December 2002, 03:54 PM   #4
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Brian,

Using three of the AD1896's sounds like a great start to a multichannel DD/DTS DAC system that many have been interested in on the forum.

I wonder if using this method (3 separate stereo DACs) off of 3 AD1896's would reduce any crosstalk problems, compared to using an AKM AK4357 or Cirrus AK4362 multichannel DAC. Any comments anyone? Pros? Cons?
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Old 14th December 2002, 06:33 PM   #5
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Default Truncation before the ASRC

Quote:
Originally posted by Microfast

I have read with more attention the document of the evaluation board ; it is right that the 2FS are 3 PCM outputs ( for the six channells ) and that is selectable in IIS format but only at 32 bit ( the other format for 2fs is MSB-first left justified and always at 32 bit ).

Is this 88 Khz. IIS 32 bit pcm format ok for the AD1896(5) ?
Yes.
Even though the largest input word size the AD1896 can handle is 24 bits, the input frame size is still 32 bits. The AD1896 will simply ignore the 8 least significant bits.

Normally, it would be desirable to add dither to round the data from 32bit to 24bit, instead of just truncating it. Because the AD1896 performs a 'curve fitting' operation on the incoming data, pre-dithering it is less important.

I suppose having dither between these parts might conceptually provide a minute improvement, but I believe this will be below other rounding errors that are likely to occur in the data path.

BTW,
The AD1895 isn't suitable for multi-channel, because it doesn't support matched-phase mode. It will work for stereo. If you want to do multi-channel, you'll need the AD1986.

Brian.
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Old 14th December 2002, 06:49 PM   #6
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Quote:
Originally posted by Tieftoener
I wonder if using this method (3 separate stereo DACs) off of 3 AD1896's would reduce any crosstalk problems, compared to using an AKM AK4357 or Cirrus AK4362 multichannel DAC. Any comments anyone? Pros? Cons?
It seems to me that, everything else being equal, a two channel DAC wouldn't have any inherent crosstalk advantages over a six or eight channel DAC. I suppose using six mono DACs might offer an advantage, although this is normally done to improve dynamic range rather than for crosstalk issues.

I've been focusing on using digital amps, so I don't have as strong of an opinion of the relative merits of different line-level DACs as I might otherwise have.

You wouldn't need AD1896s to switch from a multichannel DAC to multiple DACs. The DACs you mention normally use three separate stereo data inputs to begin with.

Brian.
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Old 14th December 2002, 08:27 PM   #7
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Quote:
You wouldn't need AD1896s to switch from a multichannel DAC to multiple DACs. The DACs you mention normally use three separate stereo data inputs to begin with.
I realize you don't need the 1896s, but assuming that the designer wanted to use it anyway to upsample, it's nice to know that you have the option of using upsample for more than two channels (i.e. using the two other 1896s in slave mode). That's all I was getting at.
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