Re: clicking in cw program
Joop,
I had an email exchange with Simon after my mail to this group yesterday.
His response follows.
--
Eric Krohn KC0CAV
To: Eric Krohn <krohn@ekrohn.com>
From: Simon Baldwin <simonb@sco.com>
Date: Wed, 07 Jan 2004 12:49:50 -0800
Subject: Re: clicking in cw program
Eric,
Thanks for your interest in the program, and your email.
The click you refer to is caused by something which is called, IIRC,
the Gibbs effect. For speed and accuracy, Unixcw is actually gener-
ating tone data all the time, and to get its keying effect, relies
instead on gating the tone data through the soundcard by setting the
PCM sound volume to either zero (silence) or to the set volume level.
Unfortunately, gating sound like this causes 'hard' edges where the
gating happens anywhere except on a sine wave zero crossing, and the
harshness of the effect depends somewhat on where in the sine wave
the on/off gating happens. These hard edges to the audio stream are
what cause the popping effect.
I've tried to get round it, but it's hard to do given the fundamental
way that Unixcw works. There's no way to query the soundcard to see
when a sine zero crossing occurs; awaiting this would have been the
best way to resolve the issue, but it's closer to real-time computing
than Linux will allow.
It seems that the problem is worse on some soundcards than on others.
My own isn't too bad at all, but it is affected. Adjusting volumes,
to use more speaker amplification and less soundcard drive, or vice
versa, might help, and you may also get some mileage out of varying
the tone frequency (higher/lower probability of getting a hard edge
when gating the tone). But fundamentally, I haven't yet found a sol-
ution, nor is there any update to Unixcw beyond the one you're using
from Debian.
Given that someone else recently asked about this too, I'll see if I
can take a second look, to see if anything can be done about it, when
I get the chance. I'm not sure what, though, at the moment, as the
current demands of the program verge on timings that the Linux kernel
may not be able to deliver, at least, not without resorting to device
driver code and tweaks. If I do happen to come up with some clever
way around this, I'll drop you a line.
Thanks again for your interest in the program, and best regards,
--S
--
-----Original Message-----
Eric Krohn wrote:
> I've been using the cw program from sarge (2.2-7) with sound card output.
> Every dit and dah sounds with a bit of a click at the beginning and end.
> It gets very annoying as the wpm increases (dits and dahs get shorter
> relative to the duration of the clicks).
>
> I don't notice it with the console output, but my builtin PC speaker is
> far away and muffled by the fan noise, so I'd rather get the sound card
> output working better.
>
> Has anyone else run into this problem? Is there a fix?
>
What about contacting simon baldwin, the author of unixcw? I have worked
with him in the past on beta versions of unixcw and he has always been
very helpful fixing things.
Simon's homepage is at http://www.geocities.com/simon_baldwin/ where you
can find his e-mail address.
Maybe a low-pass filter between the sound-card and your amplifier could
also eliminate clicking.
> --
> Eric Krohn KC0CAV
> who needs only to pass the 5wpm code test to upgrade to Extra!
>
>
Regards,
Joop PG4I
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