FT-8 WSJT audio output fluctuation on Windows, but not on Mac

[F4LHZ]

Hello,

I'm doing FT8 since a few weeks without any problem, with an Icom IC-705 linked via WiFi (with the IC-705 in Access Point mode) to my MacBook that runs wfview and WSJT-Z (and VB-Audio Cable's virtual cable to link wfview and WSJT-Z).
Here's an exemple of the audio output modulated by WSJT-Z :



It's nice and clean, no issue

But the MacBook is my main computer, and I don't want to take it with me on occasional trips where I could work some FT8 away from the QRA.
So I installed VB-Audio, wfview and WSJT-Z on a PC laptop that I have, running Windows 10.
I configured everything exactly the same as on the MacBook.

But when transmitting, the power output is not stable... it varies constantly on the Po-meter, from about 50 % to 100 %, and when I check the Audio view like above, I can see that the audio output is indeed not clean at all : there's a spike at the main frequency, but the transmission is spread on 4 kHz around it
The output level is going up and down of course, so I took different screenshots during the 15 seconds of TX, to give an idea of some of the phases it goes through :



I tested many things to try and correct this, but to no avail :

• Changing the TX codec in wfview
• Changing the sampling rate in wfview
• Changing the audio system in wfview
• Changing the power output level in WSJT-Z
• Changing the sampling rate in VB-Audio's Control Panel
• Sending a single tone of say 1500 Hz by entering @1500 in WSJT-Z's Tx6 field (same result)
• Installing the same version of WSJT-Z than the one used on the MacBook (which is a bit older than the Windows version)
• Disabling "exclusive mode" in VB-Audio's properties in Windows' sound properties
• Rebooting everything multiple times since I'd had the problem, of course

I don't understand why the PC can't TX a simple tone like the Mac... that shouldn't require a lot of power after all (nothing else is running on the PC, anyway).

If somebody has an idea...

Thanks and 73

 

[merlin]

Hmm, could your TX audio level be too high ?
Only thing I can think of off the top of my head.

 

[F4LHZ]

Actually I found a fix while waiting for the post to be validated, but I kept the post open in case it's useful to somebody with the same issue in the future :

In Windows' sound settings, I edited the advanced properties of each VB-Audio's Cable virtual interface and forced them both to use a sampling rate of 48 kHz in 16-bit.
When I did this for the "output" cable interface, Windows warned me that this interface was currently in use by an application (but I don't know which one, since I had wfview and WSJT closed before) and that it had to stop this app.

Since then, everythings works fine.
I've made some QSOs using the PC since, so it seems ok now

73