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Message #01140
[Bug 513942] Re: truncated CW dah's on some audio devices
** Changed in: unixcw (Debian)
Status: New => Fix Released
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https://bugs.launchpad.net/bugs/513942
Title:
truncated CW dah's on some audio devices
Status in “unixcw” package in Ubuntu:
New
Status in “unixcw” package in Debian:
Fix Released
Bug description:
Binary package hint: unixcw
For some audio devices (soundcards) the 'cwlib' library generates
truncated Morse code elements (dah's and dit's) due to audio buffer
underruns.
'cwlib' works by assuming that it will be able to store at least one
second of audio in the audio card fragment buffers (given the 8192 Hz
DSP rate and 128 byte fragment size that it tries to set up). Audio
devices which do offer enough buffers to satisfy this condition do not
exhibit this bug.
But some audio devices do not offer enough buffers (at that particular
rate anyway) to hold that much audio data, or even enough for a whole
Morse code "dah" at the default 12 WPM Morse output speed. On such
devices, all the dah's get truncated when the audio buffer underruns.
Setting the Morse WPM speed to a higher rate alleviates the problem
(because the dit's and dah's are shorter so cwlib refills the audio
buffers frequently enough to keep up). Likewise setting the Morse WPM
speed to a lower rate exacerbates the problem.
TESTCASE:
A Morse code K should sound like "-.-" (dah-dit-dah)
echo K | cw # 12 WPM underruns: sounds like "- .-"
echo K | cw -w 20 # 20 WPM is fine: sounds "-.-"
echo K | cw -w 4 # 4 WPM underruns: sounds like ". . ."
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