Home > USB AUDIO > C-Media CM6631A Firmware Tool

C-Media CM6631A Firmware Tool

October 11, 2013 Leave a comment Go to comments

While testing a CM6631A interface, I discovered that for 44.1K/48K sample rate material, the bitclock was running at 128FS (rather than the more common 64FS). Thus when connected to a Sabre 32 DAC, it reported a sample rate of 88.1K/96K. I described the behavior as “2X bitclock” [link].


BLCK is the same for both 44/48K and 88/96K. This means that for 44/48K sample rate, the data is running at 128fs and for the rest of the sample rates, it is running at 64fs.

Even though the Sabre32 DAC specifies BCLK to be 64 fs, it appears that it also supports  128fs. Why? because when I play 44.1KHz material, the DAC reports 88.2KHz sample rate and it sounds perfectly fine. (The sample rate reported by the Sabre32 DAC is  based on the frequency of the bitclock, the DAC reports 88.2KHz for 44.1K material)

C-Media, announced the availability of a firmware tool that allows the selection of the bitclock frequency and other parameters [link]


It creates a hex file when you click “Generate FW”. The destination folder must be the folder where the file “UsbDac.bin” (which comes with the config tool) is located


In order to “fix” the “2X bit clock” issue, you need to select x64 BLCK. For the DIYinhk board, you also need to select “Speaker” for Terminal Type and “I2S Format”


Then you need the “Firmware update tool” to upload the s/w to the CM6631A-based interface.


There is instructions included with the FWUpdate tool. If you need a copy, you can ask user tdtsai at diyaudio [link]

Once you update the FW with the x64 BCLK rate, the 44.1K/48K sample rate will correctly display in the Sabre32 DAC.

Diyinhk has a new version of this board that also takes advantage of the config tool to generate different versions of the firmware [link]

  • The board has two I2S output is available. The diyer can flash the firmware and enable “Headphone I2S” (non-isolated) and “Speaker I2S”  (isolated) if needed.
  • The SPDIF (coaxial /optical) connection is routed out for diyer to mod (tap) if needed
  1. November 26, 2013 at 12:43

    I hope that you can help me. My CM from diyinhk with ES9023 board from him also acts weird: it is playing ok, buy suddenly it stops and only sound is a high freq. tone, i have no idea how to fix it. Best Regards

  2. November 28, 2013 at 13:55

    I’m looking for the configuration tool of CM6631A, and I have known that it’s provided by Mr. tdtsai but now I couldn’t contact with him. Could you send me a copy of it? My E-mail is ry900814@hotmail.com. Thanks for your enthusiastic help!

  3. Alexander
    December 20, 2013 at 22:59

    It is very intresting for tests…. can you send me this file? Email on click an icon

  4. Peter
    January 21, 2014 at 10:05

    could you please email me this tool?
    Thanks a lot!

  5. May 4, 2014 at 19:59

    Thanks for useful info, i’m trying to get my CM6631A based card to play with raspberry / RaspyFi player and need to enable s/pdif output in firmware (Is done in the driver when used with PC) – Is it possible to get you to e-mail the Configuration tool described in this article? Thanks in advance! /best regards! /Goran

  6. Roberto
    October 3, 2014 at 19:15

    I have a CM6631A based PD04 DAC that doesn’t work at 176/192. Can I have the firmware configuration and update tools?
    Thanks a lot in advance

    • Gabriel
      October 23, 2014 at 20:42

      I have also CM6631A based PD04 DAC. It is new with 1.01 firmware and plays only up to 96kHz, so 176/192kHz doesn’t work too. Did you Roberto find any solution?
      Thanks a lot

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