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Old 6th December 2002, 12:02 PM   #1
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Question Upsampling DAC and De-Emphasis flag?

Question is: The receiver chip has an EMFLG (DIR1703) or /EMPH (CS8420) output, to indicate that the input data has the De-Emphasis flag set, and that de-emphasis has to be done on the data, analog or digital. Now I feed this data to an asyncronous sample rate converter (AD1896 or internal ASRC of CS8420) to upsample to 96kHz. No problem yet. But the digital filter df1706 (or df1706) can only handle digital de-emphasis on Data up to 48kHz. Is this related to the original sample rate? Can I use the EMFLG to drive the DEM input of the DF1706?

I know that there are very few CDs with Emphasis, but should work.

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Old 6th December 2002, 12:13 PM   #2
tiroth is offline tiroth  United States
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The coefficients change depending on the sample rate. So you may assert DEM at 96kHz, but either the response curve will be wrong or the filter will not acknowledge it if it does not support 96kHz.
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Old 6th December 2002, 01:45 PM   #3
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Note also that this flag is very unimportant in real life. In my CD collection I have only 10 CD's with emphasis and those CD's are från the stone age. My DAC has this filter and if you switch it on and off you will get a rather small change, only 2-3 dB( ?? not sure about the dB, slightly audioable) higher treble. This is possible to live with.

Deempasis is only on 44.1 kS and CD's.
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Old 6th December 2002, 02:01 PM   #4
tiroth is offline tiroth  United States
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Well, in some cases it would be nice to have DEM at 96kHz (e.g. we are upsampling 44k1). Otherwise we need to prefilter for deemphasis, then upsample. I came to the conclusion myself that I could live without it in my design though.
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