CS4396 DAC, Can the filter be changed??

primalsea · 21st January 2008, 01:09 PM

I have a DAC with the CS4396 chip and would like to modify the analog filter frequency and order.

The CS4396 has the analog filters built in. Even though it is a oversampling device it still seems to follow the odd trend of having the filter immediately after 20Khz.

If anyone can explain why DACs have this please do. I thought the whole point of over / up sampling was so that the filter cutoff could be higher?

Is it possible, by hook or crook, to change the internal filters frequency?? There are some filter pins but 'm not sure if these relate to the analog filter or the digital filter used in the oversampling process.

Anyone help????????

leadbelly · 21st January 2008, 05:13 PM

Quote:

Originally posted by primalsea
If anyone can explain why DACs have this please do. I thought the whole point of over / up sampling was so that the filter cutoff could be higher?

http://en.wikipedia.org/wiki/Nyquist_rate

primalsea · 21st January 2008, 08:07 PM

Thanks for the link, but I don't think thats the answer to what I asked.

I thought the point of oversampling was that the aliases were pushed higher up in frequency so brickwall filters at 20Khz were not needed.

This was just a side question anyway, the main one is if the frequencies of the built in filters can be changed.

leadbelly · 21st January 2008, 08:13 PM

Quote:

Originally posted by primalsea
I thought the point of oversampling was that the aliases were pushed higher up in frequency so brickwall filters at 20Khz were not needed.

Assuming that the original analog signal was digitised at 44 kHz (CD), you can do all the hocus pocus you want in the digital domain, but you cannot extract more than 22 kHz of bandwidth out out of that signal without aliasing.

SoNic_real_one · 21st January 2008, 11:34 PM

Yes, but his question was probably about the 96kHz and 192 kHz sampling.
My guess is that the oversampling is done in order to use simpler filters (low order) with a nicer phase carcateristic and sound. Brick walls are a pain to make.

From the datasheet , I see that at 96kHz you have 40kHz bandwidth and at 192kHZ you have 73kHz bandwidth with your DAC.
Look at page 6, 23, 24 in data sheet.

primalsea · 22nd January 2008, 12:05 PM

At the moment I'm looking at just 44.1Khz. I've had success just using a 2nd order 50kHz filter after a dac.

I was hoping to push the filter freq out on this dac to as far as possible.

SoNic_real_one · 22nd January 2008, 10:02 PM

It is useless to push it over 20kHz... it is actually bad for sound.

21st January 2008, 01:09 PM	#1
primalsea diyAudio Member Join Date: Apr 2003 Location: Suffolk UK	CS4396 DAC, Can the filter be changed?? I have a DAC with the CS4396 chip and would like to modify the analog filter frequency and order. The CS4396 has the analog filters built in. Even though it is a oversampling device it still seems to follow the odd trend of having the filter immediately after 20Khz. If anyone can explain why DACs have this please do. I thought the whole point of over / up sampling was so that the filter cutoff could be higher? Is it possible, by hook or crook, to change the internal filters frequency?? There are some filter pins but 'm not sure if these relate to the analog filter or the digital filter used in the oversampling process. Anyone help???????? __________________ Primalsea

21st January 2008, 08:07 PM	#3
primalsea diyAudio Member Join Date: Apr 2003 Location: Suffolk UK	Thanks for the link, but I don't think thats the answer to what I asked. I thought the point of oversampling was that the aliases were pushed higher up in frequency so brickwall filters at 20Khz were not needed. This was just a side question anyway, the main one is if the frequencies of the built in filters can be changed. __________________ Primalsea

22nd January 2008, 12:05 PM	#6
primalsea diyAudio Member Join Date: Apr 2003 Location: Suffolk UK	At the moment I'm looking at just 44.1Khz. I've had success just using a 2nd order 50kHz filter after a dac. I was hoping to push the filter freq out on this dac to as far as possible. __________________ Primalsea

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21st January 2008, 11:34 PM	#5
SoNic_real_one diyAudio Member Join Date: Jan 2008 Location: Virginia	Yes, but his question was probably about the 96kHz and 192 kHz sampling. My guess is that the oversampling is done in order to use simpler filters (low order) with a nicer phase carcateristic and sound. Brick walls are a pain to make. From the datasheet , I see that at 96kHz you have 40kHz bandwidth and at 192kHZ you have 73kHz bandwidth with your DAC. Look at page 6, 23, 24 in data sheet.

22nd January 2008, 10:02 PM	#7
SoNic_real_one diyAudio Member Join Date: Jan 2008 Location: Virginia	It is useless to push it over 20kHz... it is actually bad for sound.

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