[Bug 513942] [NEW] truncated CW dah's on some audio devices

[Kamal Mostafa]

Public bug reported:

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 ".     .  ."

** Affects: unixcw (Ubuntu)
     Importance: Undecided
         Status: New

** Description changed:

  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 should 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: like ".     .  ."
+ 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 ".     .  ."

-- 
truncated CW dah's on some audio devices
https://bugs.launchpad.net/bugs/513942
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