TOPIC:

I am looking for a way to synchronize the I2S clocks to an external clock oscillator. I have just measured the I2S clocks and the 13MHz crystal oscillator output. They do not seem to be locked together. This is consistent with what you stated on DIYAUDIO:

"It's using a 13Mhz oscillator but that 13MHz is only for the USB Phy though. Not for the audio signal."

Is there another clock which can be controlled from outside and which is used to derive the audio clocks? Or how are the audio clocks generated?

In the same post on DIYAUDIO it was also stated:
"Future firmware rev will have the ability to input a MCLK if those of you want to input their own MCLK>"

Is that still the plan?

The clocks on the I2S simply aren't clean enough for critical applications. Therefore I am interested to find a way to synchronize to a very clean external master clock. I think I have a way to do this for the Toslink interfaces, but it would be better if the I2S interface could be used, to get more channels and simplify the interface design.

At this point of time, no plans to enable an external clocking on the USBStreamer I'm afraid since we have quite few things on our plate and is a bit of a low requirement feature based on the use of the module with our OEM. If you want to use a device as Master combined to the USBStreamer, the easiest path being to use an ASRC in between the 2.

DevTeam

I'm looking for the ability to use an external clock also.
I have a 10 channel DAC with local ultra-low jitter clocks. I'm looking for a way to make my DAC the word clock source for the USB Streamer.
I'd also like to know if the SPDIF output is in sync with the I²S or a sample or more behind and what pahse relationship it has to the FCLK. To get 10 channels from this device I need all 4 I²S ouputs plus the SPDIF. I'm happy enough to remove the Toslink from the board and take the TTL directly to a SPDIF receiver. Likewise, I could remove the SPDIF Toslink input and send TTL SPDIF directly to the reciever input and use this input to create a word clock. Whether everything will remain in relative phase sync is the real question though...

Any chance of the circuit diagram of the USB streamer so I can work out how and if it can be modded? Is the driver source code available to modify to create a word clock input and GPIO output to control the external clock selection of 24.576MHz / 22.5792MHz clock source for changing sample rates?

I managed to do it with a special interface that I made for this purpose. See:
Master clock and isolator for the MiniDSP USBStreamer

I have designed and built the simplified version as well, but I have not tested it yet. I am confident that it will work though, since I basically just removed the crystal oscillators and and some circuits related to these. The basic principle is the same. I hope to be able to test it within a week or so.

I have not implemented the Toslink part, since I have no use for it at the moment. But the PCB is prepared for an add-on board with Toslink/SPDIF receiver and/or transmitter.

I don't know the the timing of the data signals being sent out from the USBStreamer on the Toslink relative to the I2S channels. But an added Toslink receiver will add some delay, perhaps 1 to 4 samples, depending on the type used. The LRCK and SCLK can be synchronous to the I2S channels though. The data would just be delayed a few samples. For most applications I don't think that will be a problem. I we imagine that there is a delay of 5 samples, it would be around 100us at 48kHz sample frequency. For playback via speakers this would be equivalent to moving the delayed speaker channels approximately 3.4cm.

Perhaps devteam could help us with information about the relative timing of Toslink versus I2S? (Just assume that the internal clock is the clock master in this case, not the Toslink input).

Thanks for your reply - looks like you've already done a fair bit of work.
I hadn't thought about just detecting the on-board clock output and replacing it with an off-board one, excellent idea!

I think I can easily implement this in a simple logic array and use some high speed isolators to the DAC's. I already have the clocks on my DAC board so it's a simple job to buffer similarly to what you've done and send the select MCLK back to the USBStreamer.

I'm using 5 x PCM1794 DACs which feed differential LPF output I/V filters using 4 x AD797 op-amps each and 5 x PGA4311 volume controls on the balanced outputs. This means the DACs through to the output is fully diferential. Yes, 20 x AD797 was quite pricey but this is a failry non-compromise design. The 5 stereo channels feed a 5-way active speaker.

Your comment about the SPDIF being 1-4 samples delayed won't be a problem as it only feeds the low frequency 20-70Hz. If a 1-4 sample delay is an issue I can just delay all the I²S channels by whatever the delay turns out to be.

Thanks for your input - maybe there needs to be a USBStreamer modding section added to the forum (is it allowed)?

@ Jens,

That's a great setup which we weren't aware off! By all means do keep us updated of your progress... Neat setup.

To those of your thinking about "modding" your USBStreamer. Do pay attention as you may not all have the knowledge (soldering/electronic) that Jens has this being said. I'd just want to make sure we don't imply that tweaking a board with a BGA module (XMOS) is trivial. Heat up the board too much and you will create permanent damage to the BGA ball, i.e. no connection and not something you can "rework". We do have software here able to run test on each BGA pin.. So you're all warned.

Devteam

I have just made a modified version of the isolated interface. It is now possible to use other MCLK frequencies than the usual 24.576 MHz / 22.5792 MHz. The new version accepts inputs of half or double of these frequencies. A jumper option selects between x0.5, x1 and x2. See:

Master clock and isolator for the MiniDSP USBStreamer

The tweaking of the USBStreamer is not that hard. You don't need to solder the BGA (which I would certainly not recommend to anyone), but you do need a small soldering iron and some soldering skill.

Wow... Great progress Jens! Is that a board that you're selling separately?
How do you connect to it? Any little app note?

Devteam

In Mac's Audio/Midi setup, there is a choice of Clock Source. However, the deceive only passes audio when 'USBStreamer Internal Clock' is selected. If external doesn't work, why is there a choice? PS: I would like to clock the USBStreamer from my RME.

@ Niko,

Mmmh, not sure what could be the case here.. Is your RME already configured for clocking out? (i.e. both device in Slave maybe the issue?)
We can investigate here to see what could be the cause. Works fine under Windows so much be something specific here.

DevTeam

The RME is set to Internal Clock and therefore should send word clock via ADAT. Not sure why the USB Streamer is not receiving it (I assume). I read through the RME manual (it is an RME ADI-8 Pro) and can't find anything that would indicate a particular setting. I will see if another device will clock from the RME via ADAT. Please let me know if you find anything out that in the meanwhile. Regards

Did you set the Optical out to be the SPDIF Out in the RME HDSPe settings? If you don't do that SPDIF will default to the COAX output only. SPDIF won't lock to an ADAT clock, only to a SPDIF clock; they are different.

After several tries it worked. It had to do with the order of changing settings. From memory: The settings in the Audio/Midi preferences have to be changed/set BEFORE opening Logic. Will try it again and confirm. The MiniDSP worked flawlessly!

@ Niko,

Thanks a lot for the update and glad to hear that it worked! We'll investigate the sequence to see if that's related and document the good info you've suggested to the user manual. Have fun,

DevTeam

Hello,

I would like to use my RME ADI-8 DS with a new macbook pro. Will the USBStreamer B work? I see Niko got it to work with an RME ADI 8 Pro which is very similar.

-Thanks,
Fabricio

P.S. Where can I buy a unit in Spain/Europe?