Frequently Asked Questions

Filters - Possible to shed more light?
We have a presence on Head-fi which we post a few technical pieces. You can find information regarding the filters in more detail:

http://www.head-fi.org/t/711217/idsd-micro-crowd-designed-phase-2-iclub-video-announcement-page-127/1050#post_10662147

&

http://www.head-fi.org/t/711217/idsd-micro-crowd-designed-phase-2-iclub-video-announcement-page-127/615#post_10591026

Furthermore:

What does the iDSD Micro filter settings in DSD actually do?

DSD must use a very high filter, in order to avoid sending twice as much noise as maximum signal from 1/2FS to FS downstream. For standard DSD, this means the 1.4MHz to 2.8MHz band.

To deliver that we use:

1) A fixed, 2nd order low-pass at 80kHz after the DAC.

2) For DSD an analogue FIR filter is built into the DAC. This allows very strong filtering.

3) The different filters provide alternative trade-offs between removing unwanted high frequency noise, transient response and signal levels.

4) The respective FIR analogue filter frequencies (-3dB) selectable are (IIRC) 77kHz, 95kHz and 185kHz or thereabouts.

So the most narrowband filter doubles attenuation of frequencies around 80kHz compared to the 185kHz filter, while the 185kHz filter is so high that for most things, the 80kHz analogue filter dominates. The final one is inbetween.

Generally speaking, steeper/more attenuated filters have worse transient (squarewave) response and better filtering of the high frequency noise.

What should I ideally use?

3 Digital filters (for PCM)

  • Bit-Perfect
  • Minimum Phase
  • Standard
The Standard filter measures the best.

The Minimum Phase filter reduces the unwanted pre and post ringing of the digital signal and produces a more natural sound. A lot of high end DAC's have this one.

The Bit-perfect filter originated in CD-77(called Digital Master Mode) then on AMR DP-777 (Bit-Perfect mode) and should ensure unaltered transmission of the data at its original bit-rate and sampling frequency.

3 Analogue filters for DSD:

  • Ultra-wide Range
  • Extended Range
  • Standard Range


 Last updated Thu, Jul 6 2017 2:26pm

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