Home > General > On OSF Bypass, DSD, 352.8K and 384K

On OSF Bypass, DSD, 352.8K and 384K

December 17, 2012 Leave a comment Go to comments

I’ve settled (for now) on the Amanero interface with the reclocking mod and can manually change from the following options:

  • Normal bitclock straight out from the Amanero device (supports every sample rate including 384KHz)
  • Re-clocked non-inverted bitclock (supports sample rates up to 192KHz)
  • Re-clocked inverted bitclock (supports sample rates up to 96 KHz)
  • DSD 2.8 and 5.6 are supported by all configurations

With this board I decided to test oversampling bypass as indicated in the diyaudio thread [post 1061]

Previously using a Musiland Interface and with a Buffalo II DAC with the 80 MHz clock, bypassing the oversampling filter did not work for 352K material.


This time in this configuration, OSF bypass did work. The DAC played both 352.8 and 384K material perfectly. It was theorized that OSF bypass would work only with synchronous operation. Not so, it works even in “normal” asynchronous operation such as this case even with an 80 MHz clock


The oddest thing is that now, both 352.8 and 384K material works with the oversampling filter ON! Although occasionally it would cease to work and exhibit the same “stuttering” behavior I experienced before. Here (with OSF on), switching in and out of 352.8 and 384K material and between these sample rates would result in a loud noise and glitches.

Thus in general OSF does not work with 80Mhz clocks and 352/384K material. In such situations you can bypass the OSF.


If the source material is DSD, bypassing the OSF would result in no sound.


Not only does it work with the high frequency material, but the oversampling filter bypass also works with everything else. I tried the OFS bypass setting on 44.1K and it works. How can I tell?  It sounds different. To my ears, bypassing the oversampling filter removes the “sparkle” from the DAC. Is this the “NOS” sound some people prefer?


The Amanero board can issue I2C instructions to any slave device. It can for example (and as proposed in the diyaudio discussion thread) that when the sample rate is 352 or 385K, the Amanero board can send the instructions to the Sabre32 DAC to bypass the oversampling filter. Unfortunately, it is not so simple as the register for the OSF also takes care of other parameters as shown below:

 |1| | | | | | | | Mono Right (if set for MONO)
 |0| | | | | | | | Mono Left (if set for MONO) (D)
 | |1| | | | | | | OSF (Oversample filter) Bypass
 | |0| | | | | | | Use OSF (D)
 | | |1| | | | | | Relock Jitter Reduction
 | | |0| | | | | | Normal Operation Jitter Reduction (D)
 | | | |1| | | | | SPDIF: Auto deemph ON (D)
 | | | |0| | | | | SPDIF: Auto deemph OFF
 | | | | |1| | | | SPDIF Auto (Only if no I2S on pins) (D)
 | | | | |0| | | | SPDIF Manual (Manually select SPDIF input format)
 | | | | | |1| | | FIR: 28 coefficients (D)
 | | | | | |0| | | FIR: 27 coefficients
 | | | | | | |1| | FIR: Phase invert
 | | | | | | |0| | FIR: Phase NO invert (D)
 | | | | | | | |1| All MONO (Then select Mono L or R)
 | | | | | | | |0| Eight channel (D)

In order to send the correct register value, you need to know the current setting of the register (in the simplest configuration, you can assume that the values are fixed, but in a general configuration, the values would not be fixed).

One way to do this is for the Amanero board to send a value to another I2C device. For example a port expander, turning high or low certain pin. Then the Arduino can read these pins and turn the OSF on/off.


The ^ mark indicates that the oversampling filter is on. In select mode, you can turn-off the OSF and you will see a “.” in that position


Note: A reader reported a bug on the OSF bypass code. If you have a dual mono configuration, take a note at the following section of the code:

else {
  bitSet (reg17L,5);
  #ifdef DUALMONO
  bitSet (reg17R,5);
  bitClear(reg17L,5); //“reg17L” should be “reg17R” here.
  writeSabreLeftReg(0×11,reg17L); //“reg17L” should be “reg17R”
  #endif DUALMONO
  1. Bunpei
    December 17, 2012 at 23:11

    Your observations completely match our result of experiments using SDTrans in the last two years.

    You can have a normal play of DXD sources by applying a MCLK higher than 90.3168 MHz.

    As for DSD, OSF is essential. I infer OSF does a sort of 1 bit -> multi bit conversion for DSD sources.

    • BlgGear
      December 18, 2012 at 17:14

      Thanks Bunpei, as I often say, I am a year behind your experiments. Yeah, I know increasing the clock speed would allow me to play 352/384 with OSF on. The strange thing is that some times it plays fine and other times I get the “stuttering” as though the DPLL needs some tweaking before it can lock to these high frequency sources. “Tweaking” meaning what sample rates you play prior to playing the high frequency material.

  2. Bunpei
    December 17, 2012 at 23:29

    As for the sonic impression of NOS conversion, I guess a sign magnitude type multi-bit DAC and a delta-sigma modulation type DAC might bring different effects though this is merely my assumption. In the case of delta-sigma modulation DAC, an upsampling operation is an indispensable stage.

    • BlgGear
      December 18, 2012 at 17:16

      I guess when the spec says that the DAC expects 8x external oversampling if turning OSF off, they really mean it.

  3. David Quayle
    December 21, 2012 at 10:00

    What type of sound card do you use to play your computer music?

    • BlgGear
      December 21, 2012 at 19:29

      I suppose this question is aimed at Mr Bunpei? Yeah. I would like to know too…

  4. David Quayle
    December 21, 2012 at 21:55

    BlgGear :
    I suppose this question is aimed at Mr Bunpei? Yeah. I would like to know too…

    No actually it was aimed at you🙂 but having said that I would also be interested in knowing what sound card Mr Bunpei uses as well.
    I was suprised to see my sound card says it will play 24/192, I guess times are a changing

    • BlgGear
      December 24, 2012 at 10:04

      It is not obvious what I have been using?

  5. Bunpei
    December 22, 2012 at 06:38

    I’m sorry I could not understand what the word “sound card” meant. Does it mean a sort of “Sound Blaster”?

  6. wktk_smile
    December 24, 2012 at 21:52

    Sorry my explanation was imperfect.

    writeSabreLeftReg(0×11,reg17L); //“reg17L” should be “reg17R”

    and “writeSabreLeftReg” should be “writeSabreRightReg” here.

  7. David Quayle
    December 25, 2012 at 08:58

    BlgGear :
    It is not obvious what I have been using?

    I was hoping your weren’t going to say that🙂

    • BlgGear
      December 25, 2012 at 18:54

      OK, These are the ones I’ve used long term (like months/years) in chronological order: Apple Airport Express, Musiland MINI and Musiland 03 US. I am using the Amanero board right now. Merry Christmas…

  8. David Quayle
    December 26, 2012 at 00:48

    Yes, I did some reading as I had not read all of your Blog & still haven’t, in my past reading through your blog I thought the Musiland & the Amanero where just USB interfaces & there was still a sound card in the background supplying the interface. My knowledge of exactly how computers work is very limited but I am always up to learn. Basically the Musiland must be feed by some board/interface/card or whatever from the originating computer, that’s what I was interested in, whether it matters how the music leaves the computer. I assume by what you are saying the Musiland is just like an external soundcard & the inbuilt sound card in your computer is either being ignored or is part of the chain but it doesn’t matter to the end result.

    Merry Christmas

    • Bunpei
      December 26, 2012 at 14:21

      Hi, David,

      This web page might be helpful to you.
      In my case, I use no “sound card” and use a SD memory player mainly.

  9. David Quayle
    December 26, 2012 at 21:09

    Bunpei :
    I’m very sorry that I missed inserting the link into my previous post.
    This page might be helpful to you.

    Thank you

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