Clicking-type noise on transmit audio on FT8

[VK4ADC]

I have just replaced the shack PC - which of course has different ports to the original machine. This necessitated adding another 4-port USB hub that has the USB/serial interface to feed CIV to the Icom transceiver, a USB/audio sound card device (ie FT8 audio in/out) and the USB/serial connection for my rotator control device, all connected to it.

The WSJT-X software worked with the USB sound interface, my transceiver was keyed by VOX, frequency was software controlled, and I still wasn't getting QSOs stacking up as quickly as before the hardware changeover. 

Fortunately my IC-7400 has an audio monitor button active on transmit and that was a great revealer : there were random audible clicks affecting the transmit audio quality.  
First step was to replace the USB sound card interface device - different audio levels but click sounds still there.  
Plugging the USB interface device into a different (and powered) hub just in case the original total current draw was too high : no, still clicking sounds on the TX audio.  
Found a short USB male/female extension lead so the USB sound device could plug directly into a USB port on the front of the PC (extra cable length needed) : NO CLICKING sound.

No real explanation as to why it only happened on a USB hub - powered or unpowered - but there is a lesson here. If you are re-configuring your station for digital modes , or replacing the shack PC/laptop, then have a listen to your transmit audio (eg using the Tune button in WSJT-X) and check for extraneous noises on a suitably-tuned receiver. It could save you a bit of time, and maybe heartache, because it "isn't working like it's supposed to".

The fix : Connect the USB / sound interface directly to the computer's USB port and then put other peripheral devices on the hub(/s).

[VK5PJ]

Hello Doug,
 both USB 2 and USB 3 support a fixed number of 'end points'  if you exceed or get close to exceeding the number of end point then strange things happen.

USB 3 supports less end points than USB 2 does so if you have sound devices, probably best to be on a USB 2 port.

On some motherboards the rear and front ports are on different part of the internal USB architecture so its will distribute the end points across the system for you and avoid crush points.   On some Windows systems you will see warning about the number of endpoints being exceeded, I see this on one of my SDR's (ELAD) if I connect the RX audio / data feed to an USB 3 port.

As strange as it sounds, i have CAT on USB 3 and TX / RX audio on the USB 2 ports for best performance, not exactly the logic most would expect as we would naturally think USB 3 = Better but not always.

regards,
Peter