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Subject: kern/1637: mss driver causes feedback (squeal) on some laptops
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>Number:         1637
>Category:       kern
>Synopsis:       mss driver causes feedback (squeal) on some laptops
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    freebsd-bugs
>State:          open
>Class:          sw-bug
>Submitter-Id:   current-users
>Arrival-Date:   Wed Sep 18 11:20:06 PDT 1996
>Last-Modified:
>Originator:     Nick Sayer
>Organization:
Just me
>Release:        FreeBSD 2.2-960801-SNAP i386
>Environment:
 
Zenith Z-NoteFlex, possibly others.
 
>Description:
 
Using the audio devices causes feedback howl when mic is left near  
speaker. This happens even if only audio output is being used.

>How-To-Repeat:

The built in mic on a Z-NoteFlex is close enough to the speaker that
unless headphones are used any audio playback will include a terrible
howling.

>Fix:

The default mixer setting for 'record monitor' is full on instead of full
off. This is because the "polarity" setting is wrong.

*** ad1848_mixer.h.orig	Tue Nov 14 01:58:28 1995
--- ad1848_mixer.h	Tue Sep 17 13:23:26 1996
***************
*** 95,101 ****
  MIX_ENT(SOUND_MIXER_LINE,	18, 1, 0, 5,	19, 1, 0, 5),
  MIX_ENT(SOUND_MIXER_MIC,	 0, 1, 5, 1,	 1, 1, 5, 1),
  MIX_ENT(SOUND_MIXER_CD,	 	 2, 1, 0, 5,	 3, 1, 0, 5),
! MIX_ENT(SOUND_MIXER_IMIX,	13, 1, 2, 6,	 0, 0, 0, 0),
  MIX_ENT(SOUND_MIXER_ALTPCM,	 0, 0, 0, 0,	 0, 0, 0, 0),
  MIX_ENT(SOUND_MIXER_RECLEV,	 0, 0, 0, 0,	 0, 0, 0, 0),
  MIX_ENT(SOUND_MIXER_IGAIN,	 0, 0, 0, 4,	 1, 0, 0, 4),
--- 95,101 ----
  MIX_ENT(SOUND_MIXER_LINE,	18, 1, 0, 5,	19, 1, 0, 5),
  MIX_ENT(SOUND_MIXER_MIC,	 0, 1, 5, 1,	 1, 1, 5, 1),
  MIX_ENT(SOUND_MIXER_CD,	 	 2, 1, 0, 5,	 3, 1, 0, 5),
! MIX_ENT(SOUND_MIXER_IMIX,	13, 0, 2, 6,	 0, 0, 0, 0),
  MIX_ENT(SOUND_MIXER_ALTPCM,	 0, 0, 0, 0,	 0, 0, 0, 0),
  MIX_ENT(SOUND_MIXER_RECLEV,	 0, 0, 0, 0,	 0, 0, 0, 0),
  MIX_ENT(SOUND_MIXER_IGAIN,	 0, 0, 0, 4,	 1, 0, 0, 4),
	
It is unclear whether this problem is an undetected epidemic
among mss users under FreeBSD or just another localization issue.
Perhaps this patch should have an #ifdef MSS_FIX_HOWL around it?

>Audit-Trail:
>Unformatted: