#11334 NORM 1.75-so: XO-1.75 audio sounds terrible in some configurations

Zarro Boogs per Child bugtracker at laptop.org
Fri Nov 18 02:09:10 EST 2011

#11334: XO-1.75 audio sounds terrible in some configurations
           Reporter:  dsd     |       Owner:  saadia                            
               Type:  defect  |      Status:  new                               
           Priority:  normal  |   Milestone:  1.75-software                     
          Component:  kernel  |     Version:  Development source as of this date
         Resolution:          |    Keywords:                                    
        Next_action:  design  |    Verified:  0                                 
Deployment_affected:          |   Blockedby:                                    
           Blocking:          |  
Changes (by Quozl):

  * owner:  Quozl => saadia
  * next_action:  test in build => design
  * version:  not specified => Development source as of this date


 Tested in kernel e3f598e, with volume set one step down from maximum due
 to the distortion reported in my comment to #11422.  Results:

  * regardless of channel=1 or channel=2, the output is driven to both
 speakers, and they sound equal,
  * at sample rate of 8000, and to a lesser extent at 11025, an aliasing or
 stepping tone is overlaid over the test tone, which on an oscilloscope
 shows as a stepped sine wave,
  * at sample rates of 16000 and higher, an aliasing tone is not easily
 heard, but is present according to the oscilloscope, and will be audible
 to children,
  * at a sample rate of 44100, then from 64000 to 192000, there is a
 gradual increase in random interruptions apparently caused by system
 activity, and especially wireless network activity.

 ||8000||ok aa||
 ||11025||ok a||
 ||44100||ok n||
 ||64000||ok n||
 ||88200||ok inn||
 ||96000||ok iinn||
 ||176400||ok iiin||
 ||192000||ok iiiin||

 Letter key:
  * a = aliasing tone heard,
  * n = predicted network activity (ssh keystrokes) triggered interrupts to
  * i = unpredictable interruptions were heard.

 It is important that the aliasing is avoided, or at least tested by a
 child, by preference one with musical experience.  Adults can't easily
 assess the impact of this effect.  Connecting an oscilloscope to the
 headphone output is one way to check for the presence of aliasing.

 These results show that the hardware is being driven at incorrect sample
 I recommend that the resampling be done in software, with the hardware
 driven at 48000.

Ticket URL: <http://dev.laptop.org/ticket/11334#comment:10>
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