kern/51760: audio playback sounds bad

[martin%NetBSD.org@localhost]

>Number:         51760
>Category:       kern
>Synopsis:       audio playback sounds bad
>Confidential:   no
>Severity:       serious
>Priority:       medium
>Responsible:    kern-bug-people
>State:          open
>Class:          sw-bug
>Submitter-Id:   net
>Arrival-Date:   Mon Jan 02 10:00:00 +0000 2017
>Originator:     Martin Husemann
>Release:        NetBSD 7.99.53
>Organization:
The NetBSD Foundation, Inc.
>Environment:
System: NetBSD whoever-brings-the-night.aprisoft.de 7.99.53 NetBSD 7.99.53 (WHOEVER) #69: Wed Dec 28 20:52:33 CET 2016 martin%martins.aprisoft.de@localhost:/ssd/src/sys/arch/sparc64/compile/WHOEVER sparc64
Architecture: sparc64
Machine: sparc64
>Description:

After the audio mixing changes, playback of CD quality music sounds .. "worse".
There is a tiny noise pattern overlayed to the signal, not always very 
noticable. Sounds like a few random values are output every ~20ms
(or whatever).

Not sure how to debug this, do we have some "audio tap" feature to trace
the data sent to the hw?

>How-To-Repeat:
Play music on sparc64 with mpg123 using autri:

autri0 at pci2 dev 8 function 0: Acer Labs M5451 AC-Link Controller Audio Device (rev. 0x02)
autri0: interrupting at ivec 7a4
autri0: ac97: Analog Devices AD1881A codec; headphone, Analog Devices Phat Stereo
audio0 at autri0: full duplex, playback, capture, mmap, independent

sysctl hw.autri0:
hw.autri0.frequency = 44100
hw.autri0.precision = 16
hw.autri0.channels = 2
hw.autri0.saturate = 1

>Fix:
n/a