Home > Embedded Computing > BBB DAC DEVELOPMENTS


As many know, the BeagleBone Black I2S audio implementation is in a way superior to the I2S audio implementation of the Raspberry Pi primarily because the audio clocks can be derived from the on-board 24.576MHz clock and also through off board oscillators through an I/O pin. It its current implementation, the BBB supports the 48KHz family of sample rates with the on-board oscillator and can support the 44.1KHz family of sample rates with an off-board oscillator.

The current method of generating the clocks for digital audio in the Raspberry Pi are far from perfect. The best clocks are obtained by integer division of the on-board 19.2 MHz clock and works for 48K and 96K sample rates and only if the DAC can accept 40fs or 80fs. For anything else, the clocks are derived from the 500MHz PLL through fractional division as explained above. It has been reported that the 500MHz clock itself is derived from the on-board 19.2MHz clock through a clock multiplier.

Even with a “superior” audio clock implementation, I2S DAC development for the BBB has been painfully lagging that of the Raspberry Pi (so painful that there are no products shipping). The reason is because that there is a lot, lot more community development in the Pi than the Beagle. The RPi has just shipped its 5 millionth device [link] whereas the BBB has only shipped about 220K devices [link].

No longer.


Twistedpair Audio has been busy designing and testing external components to allow the BBB access to lower jitter off-board oscillators and data reclocking for ultimate I2S signal fidelity. These boards are almost ready for general sale [link]

Update 3/26/15: they are available for sale [link], and pretty reasonably priced given the components. (The store says “introductory pricing” though)

The mockup photo below shows (from right to left) BBB, “Hermes”, “Cronus”, and Buffalo III DAC. The board on the top is the Hermes board for the Amanero interface. With Hermes-Cronus, Amanero can use better off-board clocks if so desired.


These links explain the functionality of these boards [link], [link]

  • BBB as the source of I2S/DSD digital audio, it needs external clocks in order to support all sample rates
  • Hermes as the two-way signal isolator (clock signal into BBB, audio data signals out of BBB, and I2C in-out) and I2S/DSD switch. Hermes also has connections for a volume pot, push buttons, etc. that interfaces to I/O pins in the BBB -more details below  (priced at $40 or $16 for the board only)
  • Cronus is the clock board which can accommodate two clocks: one for 44.1KHz sample rate family and one for 48kHz sample rate family. Cronus also provides data realigning of the I2S signals (as opposed to FIFO reclocking) – more details below. (Priced at $50)
  • Clock modules. The clock modules are available separately from the Cronus board with a choice of frequencies and are priced at $35 each. You need two.
  • Total is $160 for Hermes+Cronus+Clocks. You don’t really need the Hermes if all you are interested in are the clocks, so the minimum investment is $120

Here is a photo of the updated Hermes board (the interface/isolator board between BBB and Cronus)


  • Provides isolation for audio signals with 1 -8 channels of PCM – 1 – 4 channels of DSD output
  • Provides I2C isolation
  • SPDIF output is possible.
  • Lots of headers: for Switches/Rotary encoder and drivers for indicator LEDs; USART header, ADC header for analog control; headers for external power/reset switches.
  • Prototyping area (for fun!)
  • Provision for backup battery to protect the BBB on shutdown by providing a soft shutdown(self regulating battery not included in the kit – but very easy/cheap to obtain).

Here is a photo of the updated Cronus


  • Ultra low noise low impedance power supply for clocks (adm7150)
  • A clock selection multiplexer to switch between 44.1 and 48Khz time bases (this means the source must output a clock selection signal). The clocks are isolated from each-other and the rest of the circuit by utilizing L/C filtering
  • A selectable/bypassable ultra low phase noise clock divider to supply 1:2 or 1:4 clocks to a source
  • A synchronous reclocker that re-clocks the audio from the source back to the master clock. This brings all signals back into alignment with the actual master clock regardless of source jitter. Uses Potato Semi flip-flops. To learn more, here is my crude attempt at reclocking [link]
  • SMA and uFL connectors for external clock signals (both in or out), uFL connectors for PCM/DSD output.



IQAudio’s main products to date are audio boards for the Raspberry Pi. As I wrote here [link] their DAC board is one of my favorite for the Raspberry Pi. The DAC boards for the RPi are also very popular, often sold out at the Tindie store [link]

The IQAudio BBB DAC is aimed at a full I2S DAC solution for the Beagle. A photo of a prototype is shown below.As can be seen in the photo, there are no external clocks that can be fed to the BBB. Normally a DAC operates in Slave Mode. The DAC locks to the master clock or bit clock of the source and receives the data from the source device. In the IQAudio solution, the DAC instead is running in Master mode. The DAC generates the appropriate bit-clock frequencies in accordance to the sample rate of the track being played and it “pulls” the data from the BBB. You may follow its development here [link].

According the manufacturer, the board will be available in May at a target price of $45-$60. Please send your queries and comments to IQaudio at Gordon@iqaudio.com.

Notice also the I2S headers. Possibly you can use this board and tap the I2S signals and use them for another DAC board.


Comparing with the RPi DAC which is shown below, it seems the BBB DAC uses almost the same components. The innovations are in software: drivers in the BBB side and firmware to setup and control the DAC chip.


There is also an advantage of buying a product from iQAudio (and other similar companies such as HifiBerry) in that they invest in software development (drivers) and provide many ready-to-run software distributions for your embedded computer.


Acko is also planning to release a BBB cape that is derived from their current clock/isolator board which is already a working solution for the BBB. A nice photo from this post [1828]:


The “supercape” adds battery management to the capabilities of the current clock board in an integrated package. It will provide:

  • UPS kicks in when external power is removed. On-board PWR_MON will continue to power the BBB (~1hr) or options to safely shutdown BBB immediately. Same shutdown action if battery level goes below operational level [1088]
  • High Speed Galvanic Isolation with -Synchronous or Asynchronous re-clocking.capability
  • Ultra-low jitter Dual Synchronous Audio Clock (98.304MHz/90.3168MHz or 49.152MHz/45.1584MHz options) – Master Clock
  • All buffered outputs with high drive capability
  • GHz rated switching components

The following diagrams show the work-in-progress for this cape, starting with adding a USP and interface for the BBB and the clock board to the current configuration of a fully integrated cape.

From: [1088]




From [1587]:




The Soekris R2R DAC supports the BBB in synchronous slave mode by providing the required master clock frequency as selected by the BBB. BBB is in master mode, but the DAC provides the clock

  • I2S MCLK OUT pin: Master clock output: 45.1584 and 49.152 Mhz (which can also be divided)
  • I2S FSEL IN pin: Input signal at this pin selects between 45.1584 MHz and 49.152 MHz master clock output

It works in a similar fashion as the TwistedPair and Acko solutions but it has been incorporated into the DAC.

I have yet to experiment with it myself but has been reported to work: [link]

  1. lintweaker
    March 3, 2015 at 17:10

    The twistedpear board combo has been in development, for what feels like, ages. Hopefully it will be available soon. Did not know about the IQAudio option, good to see more options.
    There is also ACKO’s ‘supercape’ in development, very interesting. Now let’s see who makes it to production first…

    • BlgGear
      March 4, 2015 at 15:48

      Thanks for sharing about Acko’s effort. I’ve added what I could find to the post. For me, I am waiting for the IQAudio implementation because it will be the lowest cost one. Not enough money for all the audio diy projects out there (which is a real good thing)…

  2. Anonymous
    March 14, 2015 at 12:11

    Twisted pear and acko look quite similar in concept, TPA being modular looks more versatile to use with other products. I’l also curious about IQaudio’s solution for secondary sistem use.

    • BlgGear
      March 14, 2015 at 18:31

      Yes. About the IQ audio, the DAC chip may be programmed for master mode, and the BBB as slave mode (because I don’t see any clocks on the board). If a separate DAC is used, it may be possible to tap onto the I2S signals because it would treat the whole system (the BBB and the IQ board together) as a master device and synch to it. (At least I think how it would work)
      The Acko and TPA boards would treat the BBB as a master device and provide the two required external clocks.

  3. March 17, 2015 at 23:36

    New bbb DAC+ sounds great – but how many should we produce? Say at £45 each with headphone amp too?

    It’s based in the hugely successful pi-DAC+ but in master rather than slave mode.


    • Anonymous
      March 20, 2015 at 07:58

      The pcm5122 is in master mode and the bbb is acting as a i2s slave. (This is opposite of the pi setup).

      We’re still testing at the moment and there will be a board spin too before release. May availability is the plan.

  4. Anonymous
    March 19, 2015 at 23:41

    Gordon, so your DAC+ solves the clock issue of the BBB? will it feed the BBB the dual clocks necessary for all sample rates from 44.1 to 192?

    If yes, then at 45 you have a great alternative to the raspberry pi based systems and might sell quite a few.

    • BlgGear
      March 20, 2015 at 04:29

      I think the way it is solved is by running the DAC in master mode. The DAC is programmed to “pull” data from the BBB by driving it with the bitclock and LR clock.

  5. March 24, 2015 at 15:47

    Another one is developed by brian on dangerousprototypes.com: http://dangerousprototypes.com/forum/viewtopic.php?p=60446#p60446

    • BlgGear
      March 25, 2015 at 03:34

      Oh, yes. I was following that blog…

  6. March 24, 2015 at 15:56

    Quick update – been playing back various formats and frequencies up to 192/24 this past few days on the BBB-DAC+. I can’t say I’ve systematically tested every frequency but the common ones all appear fine. The design is very similar to the Pi-DAC+ other than the PCM5122 is I2S master on BBB.

    More details when we have them.

    • BlgGear
      March 25, 2015 at 03:35

      Thanks for the update…

  7. March 31, 2015 at 21:16

    maybe a little off topic but I was wondering what was your favorite reasonalbe dac board so far soundwise? I understood that you liked the berry dac and iqaudio, but what about ess9018mk2 or the “veritas one” for exemple. I’m looking for a reasonnable good sounding dac board. best regards. Dookie182

  8. Simon
    July 20, 2015 at 14:46

    Just to say I spoke to Gordon at IQaudio and he said that the BBB-DAC+ is now stalled. He doesn’t think that with the advent of the Raspberry Pi2 there will be any commercial attraction for buyers to go with the BBB

    • BlgGear
      July 22, 2015 at 02:42

      Seems like a prudent business decision. I checked the latest numbers of BBB shipped and it seems to be going down…


      Too bad….

  9. October 16, 2015 at 11:32

    Just a small correction regarding the Soekris R2R DAC and the MCLK and FSEL pins. The DAC provides with a 24.5764MHz/22.5792MHz but up to firmware 0.99 the FSEL does not seem to work. So MCLK is always 24.5764MHz whatever the FSEL is set.

    • BlgGear
      October 16, 2015 at 18:23

      Thanks. It was reported working in the old firmware, but I have not tested it.

  10. Frank
    April 2, 2016 at 09:36

    One question: In order to make the BBB work with the external masterclocks: Is the Frequencen select- Output Signal always needed ?…so, if a DAC or a Fifo or a Masterclock not having a fs_sel-Input: It cant be used to provide both frequencies 22.x and 24.x ?

  11. amix
    May 27, 2016 at 23:29

    Check this out: http://www.streamunlimited.com/products/wifiaudiocape.html

    Is a BBB audio cape by a commercial OEM manufacturer. They were the Philips streaming division, as it seems.

  12. September 14, 2016 at 14:49

    Modern sofas

  13. September 14, 2016 at 16:10

    Terrible Spanish School in Buenos Aires

  14. September 14, 2016 at 18:10

    wideofilmowanie lublin

  15. September 14, 2016 at 18:30

    Ink Cartridges

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