[Solved] Crap ! I seem to have a USB buffering issue.

Take a look at this video:

Because of the bad propagation i was trying to make some QSOs on JT65 and i was not able to get any response from anyone. So, because i don’t use WSJT-X a lot and because its CAT always interferes with RUMlog and CubicSDR who also want a CAT connection, i just went over the initial setup again.

At some point in the manual it says: “Click the Tune button on the main screen to switch the radio into transmit mode and generate a steady audio tone. Listen to the generated audio tone using your radio’s Monitor facility. The transmitted tone should be perfectly smooth, with no clicks or glitches.” So that’s what i did and the above video showed. So what’s next? How do i solve this?

I tried with FLdigi to send a long PSK31 signal and the same behaviour shows. I tried with my old MacBook Pro and that one works fine. Crap! Can i not use any digital modes anymore now??

So i sent the following message to the Apple forums and to the Silicon Labs Community:

USB buffering MBP 2001 vs 2015?

I am a HAM and i am using my Early 2015 MBP for data communications. I seem to have a problem where the USB ports are not able to handle the traffic going from my software to the radio.

I am using a USB cable running at 115200 between my radio and the MBP. You can see the behaviour in this video: https://www.youtube.com/watch?v=-cxr5axl_60

In this video i first put a continuous tone on the USB port. The effect should be that the radio sends out this continuous tone on the air. However, as you can see in the video, the audio is interrupted and gets worse over time up to the point that the USB port is not receiving any data anymore and the transmit signal gets interrupted.

I tried this with various USB cables and various different programs and the behaviour is the same with all.

In the video you can also see that i am sending out a CW signal not using the MBP and that signal is clean.

Why do i think it’s the MBP? Because i tried a Late 2011 MBP running the same OS as my 2015 one (Sierra) this morning and that MBP doesn’t have the issue.


Any idea what has changed in the USB handling between 2011 and 2015?

Any idea how i can manipulate the buffering if the USB port on the 2015 MBP?


Thanks for your input,



No answers yet…


When i set the audio preferences in WSJT-X like this i don’t have the issue:


I opened a ticket with Silicon Labs explaining the issue and they have sent me a previous version of the driver. This version doesn’t show the above behaviour. So i’m a happy camper again.