#11422 HIGH 1.75-so: G-streamer sine tone test does produce 'humm' over the sound

Zarro Boogs per Child bugtracker at laptop.org
Fri Nov 18 01:32:36 EST 2011

#11422: G-streamer sine tone test does produce 'humm' over the sound
           Reporter:  erikos    |       Owner:  saadia                            
               Type:  defect    |      Status:  new                               
           Priority:  high      |   Milestone:  1.75-software                     
          Component:  kernel    |     Version:  Development source as of this date
         Resolution:            |    Keywords:                                    
        Next_action:  diagnose  |    Verified:  0                                 
Deployment_affected:            |   Blockedby:                                    
           Blocking:            |  
Changes (by Quozl):

  * owner:  Quozl => saadia
  * next_action:  test in build => diagnose
  * component:  distro => kernel
  * version:  1.75-B1 => Development source as of this date


 Tested in kernel e3f598e, which includes Jon's a4143f4, on a test bed of
 six units, four B1, two C1.  Results:

  * the left and right speakers are equally loud,
  * at one less than maximum volume, the sine tone sounds normal, and looks
 perfect on oscilloscope,
  * at maximum Master volume of 100%, there is a distortion still.

 The distortion, or buzz, varies by laptop, and sounds like speakers being
 overdriven, or resonance of nearby parts.

 But when connecting the headphone signals to an oscilloscope the buzz is
 seen to be caused by a flat line on the lower half of the sine wave, as if
 the signal cannot go negative enough, ... on expanding the flat line
 section a (roughly) 25kHz sawtooth waveform can be seen imposed.

 My guess is that the buzz or humm is from the sudden change to the
 gradient of the curve, and not the sawtooth wave, 'cause I think I can't
 hear at 25kHz.  ;-}

 Unrelated to B1, so changing version.

Ticket URL: <http://dev.laptop.org/ticket/11422#comment:4>
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