Upsampling DAC and De-Emphasis flag?

pquadrat · 6th December 2002, 12:02 PM

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.

Thanks
peter

tiroth · 6th December 2002, 12:13 PM

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.

peranders · 6th December 2002, 01:45 PM

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.

tiroth · 6th December 2002, 02:01 PM

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.

6th December 2002, 12:02 PM	#1
pquadrat diyAudio Member Join Date: Oct 2002 Location: Hamburg, Germany	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. Thanks peter

6th December 2002, 01:45 PM	#3
peranders Electrons are yellow and more is better! diyAudio Member Join Date: Apr 2002 Location: Göteborg, Sweden Blog Entries: 4	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. __________________ /Per-Anders (my first name) or P-A as my friends call me

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6th December 2002, 12:13 PM	#2
tiroth diyAudio Member Join Date: Dec 2001 Location: Pittsburgh, PA, USA	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.

6th December 2002, 02:01 PM	#4
tiroth diyAudio Member Join Date: Dec 2001 Location: Pittsburgh, PA, USA	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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