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Date: Wed, 16 Dec 2009 16:10:02 GMT
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To: freebsd-multimedia@FreeBSD.org
From: Marcin Wisnicki <mwisnicki+freebsd@gmail.com>
Cc: 
Subject: Re: kern/140453: [sound] No sound inside Virtualbox on 50% volume
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The following reply was made to PR kern/140453; it has been noted by GNATS.

From: Marcin Wisnicki <mwisnicki+freebsd@gmail.com>
To: Ariff Abdullah <ariff@freebsd.org>
Cc: bug-followup@freebsd.org
Subject: Re: kern/140453: [sound] No sound inside Virtualbox on 50% volume
Date: Wed, 16 Dec 2009 17:03:12 +0100

 On Wed, Dec 16, 2009 at 02:57, Ariff Abdullah <ariff@freebsd.org> wrote:
 > Virtualbox (QEMU too) default to 5bit volume resolution, but it
 > appears through the volume resolution calibration process as
 > 6bit. Clearly, it is a "hardware" bug. Virtualbox doing
 > slightly a better job by "clamping" the results (the lower bits
 > written as '1') whenever there is a write attempt on 5th (or
 > 13th) bit, but _without_ resetting those high bit. As such, it
 > appears as a full 6-bit resolution result on the next codec
 > read. FreeBSD try to be honest here by doing supposed to be
 > correct calibration process and see/measure the result as is.
 > Others <insert whatever..> probably have their own static
 > mapping (think about vendor specific driver) or depends on
 > whatever magic marker, etc.
 >
 > You have two choices:
 >
 > 1) Fix virtualbox ac97 codec emulation (probably not for you
 >   given the fact that your vbox runs on Windows).
 >
 
 Good to hear it's a known problem. Is there any reason why this patch
 was not submitted to virtualbox (at least I couldn't find a ticket
 there) ?
 I don't really care about it since workaround is so simple, but it
 would be nice to have it working correctly out of the box.
 
 > or
 >
 > 2) "Fix" FreeBSD ac97 volume resolution calibration by
 >   accepting certain lower bits magic marker, ignoring the high bit.
 >
 >