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LF: Soundcard issues

To: rsgb_[email protected]
Subject: LF: Soundcard issues
From: Joe Taylor <[email protected]>
Date: Thu, 01 Nov 2012 11:48:56 -0400
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No AC power at home, yet. My wife and I are essentially camping out, at
home. We have plenty of firewood and a good fireplace, but we are
bored. As you will have heard, we are among the lucky ones.
I am writing this message, once again, from my university office.

A few words for those reporting "too much audio" on input to WSJT-X.

On my development system the same input level is required to make both WSPR and WSJT-X happy. Likewise on my shack computer. For example, see the screen shot posted at
http://physics.princeton.edu/pulsar/K1JT/WSJTX_WSPR.png

Could it be that those who report having to move audio level sliders far downward are using 24-bit soundcards, and their drivers are sending the low 16 bits (via portaudio) to WSJT-X? I do not presently have another explanation. I do not find any level discrepancies here. Obviously, I cannot test hardware I do not have access to.
Perhaps I should put in a digital attenuator to handle this issue?

On a possibly related matter: I am aware that a wide variety of hardware is being used to generate and receive signals on our MF and LF bands. In due course it may be desirable for WSJT-X to use 48 kHz sample rate for input, as well as output -- and even to offer I/Q input and output for direct-conversion rigs. These features have been in WSPR 3.0 for a long time, and they work well. If there is sufficient demand they could be introduced in WSJT-X as well.
At present, my available time is being spend on the JT9 decoder. With
well-behaved signals and a clean noise background, the JT9 threshold
decoding sensitivities are those given in a table at the end of the
Quick-Start User's Guide,
http://www.physics.princeton.edu/pulsar/K1JT/WSJT-X_Users_Guide.pdf .

JT9 performance may be degraded in the presence of QRM, static crashes, plasma TV birdies, frequency drift, etc. Extensive experience with JT65 on both EME and HF paths shows that most of these annoyances can be minimized or eliminated by suitable optimizations in the receiving software. These optimizations have not yet been started, in part because I do not yet have suitable examples of *.wav files recorded in difficult receiving situations.
Nobody has yet sent me a file that, when opened, produces the result
"15P6715P67WCV".
Maybe we'll have power again by tomorrow?  Or maybe not.

        -- 73, Joe, K1JT


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