• State Resolved
  • Locked Locked
  • Replies 2 replies
  • Subscribers 30 subscribers
  • Views 1298 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

DSD1794A: use of PCM or DSD output reconstruction filter?

FOTIOS ANAGNOSTOU
Prodigy 200 points
Other Parts Discussed in Thread: SRC4392, DSD1794A

Hi

With your support i finally led in the use of SRC4392 with two DSD1794A configured in monaural mode. I resulted in the DSD1794A because provides separate inputs for DSD and PCM data. I should remember you that will include in my project a USB2.0-Audio module that provides DSD and PCM data. Till now everything is going very well in the schematic drawing of project. Today, by looking in the DSD1794A datasheet the suggested analog low-pass filter for the output of DAC i got stuck again! The reason is that for PCM converted data the suggested filter (page 33) has a Fc=162KHz whilst for DSD converted data the filter (page 34) is totally different with Fc=38KHz.

I know that the out of band noise in DSD format, starts from lower frequency while in PCM format starts from a higher frequency.

My question is what i can do now? If i will implement the DSD suggested output filter with Fc=38KHz by sure will have a perfect response in DSD audio files, in the cost of strangling the high frequencies of PCM audio files? If i will implement the PCM output filter with Fc=162KHz then will have perfect response in PCM audio files but a lot of noise when DSD files will be converted?

Or if i will implement the DSD output filter the impact of Fc=38KHz on the high frequencies of PCM audio files will be negligible and so there is no reason to fear so much?

Or the inverse? I mean that the high frequency noise of DSD audio files will be negligible in the case of PCM output filter with Fc=162KHz?

What they do other constructors for this issue? Do they build special antialiasing filters suitable for both DSD and PCM audio files? Or they simply disregard the issue of PCM straggling by using the lower cut-off (38KHz) DSD filter having as priority the elimination of any noise? 

I came accross the internet for two days but i couldn't find anything about this issue.

Have you any experience on this issue? Is there a compromising output low pass filter with a cut off frequency which could satisfy the requirements of both DSD and PCM audio files? And this filter is different from those you present in DSD1794A datasheet?

Any help will be welcomed!

Thanks

Regards

Fotis

  • 0
    TI__Mastermind 27870 points
    Hi Fotis,

    You can go either way, either use one filter for both and use a lower Fc or use two different filters, one is a compromise on performance, but less cost and smaller size. One thing to consider is that the human ear can only hear up to around 20 kHz, therefore some argue that there is no reason to reproduce content over 22 kHz other will argue there is a difference.

    I think you would be fine with implementing a 38 kHz filter to output both PCM and DSD audio, but you can always build out a design with one filter as a prototype, and populate one with a 38 kHz filter, and another with a higher cutoff, and listen to both. Then decide which you like better.

    Justin
  • 0 in reply to Justin Bohr
    Prodigy 200 points

    Hi Justin and thank you very much again! 

    You should know that i already followed the way of the sharp roll-off 38KHz reconstruction filter in schematic drawing. From experience in audio i thought the same thing like you. Besides, on the actual PCB, you could remove some parts and replace some other to obtain the PCM filter of e.g. 162KHz. That is, you can use the same PCB for both filters, there is no reason to design two different boards for DSD and PCM.

    I will let you know the result after the audition test of actual models.

    Thanks a lot 

    Regards

    Fotis