Topic: Crackling Sound (1 replies)
#1     Sat Jan 09, 2010 11:24 pm
Stephens City, Virginia, USA
Join Date: Oct 2009
Posts: 57
Subject: Crackling Sound

While listening to the CW practice on 14040, I started to hear a crackling-type sound. This sound is intermittant, but occurs at least every 5 seconds. It is almost like there is a bad connection in a cable. Cables have been swapped out, with no change. This occurs through the SoundMax internal sound card.

I do not hear this sound through my USB headphones.

When I use FLDigi or MultiPSK to copy the CW, the crackling sound causes those programs to miss a letter or two. So, it seems to me, that the crackling is occuring in the sound card and not due to a connection problem from the sound card to the speakers.

My perception is that I don't hear the crackling sound during voice reception.

If I listen while sling the wave volume control up and down, I do hear a little bit of crackling sound, but not as load as the popping, static crackling sound that is causing me concern.

Does anyone have any thoughts on this particular issue? On my wife's XP computer, I do not hear this static type sound at all.

Has my sound card gone bad?

The computer is a Dell XP SP3.

Thanks for any help.

ADDITIONAL: When copying the W7TTY internet RTTY stream, the crackling sound is not heard while using Windows Media Player. It seems that this is only happening on this one computer, while copying the CW signal on CQ100.

#2     Tue Jan 12, 2010 4:34 pm
Join Date: Aug 2006
Posts: 724

Hi George,

Good question. I have noticed the same thing. The crackle happens when there is a gap in the incoming internet audio stream. It is more noticeable on CW tones than on voice.

When a crackle occurs, we increase the size of the audio buffer so the buffer won't go empty when the next gap occurs. This larger buffer increases the lag delay on the audio, so we are always trying to reduce the buffer size if no crackles are detected for a while. The buffer size is floating around, so the crackles come and go.

When you first tune in to the CW stations, the system starts with minimum buffer, then the buffer grows as a few crackles occur. So its normal to hear crackles for the first second or two when you tune to a new station. The buffer size quickly adjusts to the situation, but it's always hunting its way downward to the crackle threshold.

The problem can be at either the transmitter or at the receiver. Refer to the FAQ for advise about voice breakup.

73, Doug

P.S. I guess it could be a problem with your sound card. Try closing other programs that use the sound card. Some sound cards don't like to be shared among many programs. Try installing the latest driver for your sound card.

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