"So 0dB is OK?"

In my case yes. But I want to be clear. In my internal sound card (Motherboard), the mic input has a gain control

AND a level control. Its the gain control that makes the difference in WSJT-X receiver level floor as shown the 

the attached screen shots. 

The USB sound card has no gain control, just the level control. If the level control is set to 0, no RX audio gets

to the software to be decoded. Yet the receive level floor in WSJT-X is still 40db.

That is just plain strange.  Maybe its just a poor sound card except I don't hear the noise when I configure the

desk top speakers to listen to the mic input.

Derek

On Thursday, August 19, 2021, 08:46:18 AM MDT, Derek Toeppen <wa0zti@...> wrote:

Martin,

    Your comments turned up something.

    The cheap USB sound card input is in fact a mic input (not Line-in). I had checked earlier for a mic gain setting

as you suggested some mic inputs have. It did not have a mic gain setting, just a level setting. So I forgot all about

it.

     Prior to your comment, I had checked the behavior of the mic input on my internal (mother board) sound card. I found

the receiver signal floor was 10db (higher than the line-in of the same internal sound card that had a 5db floor). But more

importantly, that mic input does have a mic gain control. So after your comment, I adjusted it to see what would happen. 

When the gain is set to 0db, the WSJT-X signal floor is <5db (much like the line-in). At +40db (max), the WSJT-X signal floor is 40db ( just like the cheap USB mic input).

     I had previously measured the USB sound card mic input signal levels (gain) and did not think it was excessive. But 

clearly it is higher than the internal sound card line-in and that (plus maybe its general noise performance of the card) is 

effecting the WSJT-X signal floor. 

      Moral of the story, its best to use a line-in. If you must use a mic input, get one with a gain control.

Good suggestion, Thanks

Derek

On Thursday, August 19, 2021, 04:09:05 AM MDT, Martin G0HDB <marting0hdb@...> wrote:

On Tue, Aug 17, 2021 at 10:33 PM, wa0zti wrote:

I have been using wsjtx for months with the sound card built into my PC mother board. I decided I wanted to free it up
for other things so I purchased a simple USB sound card. It simply has a headphone/speaker port and a microphone
port. And I have run into something interesting with the receiver audio when I tried to use it.

[Snipped]

The 40db meter floor does not appear on the water fall display as noise and I have no trouble decoding FT-8 signals.
Any ideas why wsjtx is reacting differently to the two cards?

Have you checked the Windows settings for the new USB sound card and confirmed that the Mic gain is set to 0dB and also that there are no enhancements enabled?  I believe some sound devices can be set to provide an additional 20dB of mic gain, to accommodate low-output microphones, so you definitely don't want to have that enabled.

Also, once you've ensured that there's no Mic gain enabled for the USB sound device you might be able to reduce the audio output level from your rig (depending on the make and model of the rig) so that you get a low reading on the WSJT-X audio level 'thermometer' when there's no input whatsoever to the sound device.

--
Martin G0HDB