I've got it working fairly well in both UAC1 and UAC2 now. To the
extent that it's supported by the OS, volume controll commands arrive
as expected from iOS, OS X and Windows. Android just doesn't seem to
Windows of course doesn't do UAC1. And a bit unexpectedly, Linux
forwards volume control commands in UAC2 but applies an internal soft
volume in UAC1. I'm no Linux audio expert, and I don't know if this is
due to driver limitations or a Pulse Audio setting. So the UAC2 logic
for now is only verified in the two Apple OSes.
On Mon, Mar 21, 2016 at 4:27 PM, Matthew van Eerde
Looks like you’re advertising a hardware volume control with a range of -128******************
dB to +127.996 dB.
Channel 0 volume, -128 dB to 127.996 dB in steps of 0.0390625 dB:
Channel 1 volume, -128 dB to 127.996 dB in steps of 0.0390625 dB:
From: Børge Strand-Bergesen
Sent: Friday, March 18, 2016 4:59 PM
To: Matthew van Eerde
Subject: Re: [wdmaudiodev] UAC1 driver sends volume:0000
Report is attached. It's the Henry Audio USB DAC 128 mkII.
I ran the 64-bit version of the program while music was playing just
fine. I haven't used KsStudio before. Please let me know what to
enable there to give you the debug info.
At present the slider goes from 0% to 100%. Moving it generates a lot
of set_cur_volume activity, all with 0x0000 as the volume.
On Sat, Mar 19, 2016 at 12:46 AM, Matthew van Eerde
Is the volume control being presented by usbaudio.sys to Windows at all?
not, Windows will inject a volume APO in software.
Please run the devicetopology.exe attached this blog post and send the
Alternatively, a screenshot from KS Studio would work.
Or you can go into the Levels tab for the device in the Sound control
right-click the slider; choose “decibels”; then drag it all the way to the
left and the right to discover the minimum and maximum decibel values for
From: Børge Strand-Bergesen
Sent: Friday, March 18, 2016 4:43 PM
Subject: [wdmaudiodev] UAC1 driver sends volume:0000
I'm debugging a UAC1 interface to make the Device respond to volume
control signals from the Host. Could you help me figure out why
Windows doesn't seem to alter the volume setting it sends out? Beside
the volume control issue the Device is a fully functional DAC.
Mute control works in Windows. The device receives 0x01 for mute on,
0x00 for mute off. But for the volume setting I keep receiving 0x0000
from Windows 7 when I pull the volume control bar for the device up
and down. Windows is clearly conveying a volume setting for each user
interaction, just not the right one. I'm trying to figure out why.
Repeating a similar action on iOS and Linux I receive a variable
volume setting into the device. iOS does give out a variable volume
setting, it just does not seem to be in accordance with the min and
max values. So Windows and iOS are confused in different ways by what
is perhaps the same bug.
Linux is the most forgiving of the three and gives out variable volume
within the min and max bonds. I haven't yet tested with OS X.
The volume control system is based on Atmel mcu code which responds to
such things as
#define BR_REQUEST_GET_CUR 0x81
#define BR_REQUEST_GET_MIN 0x82
#define BR_REQUEST_GET_MAX 0x83
#define BR_REQUEST_GET_RES 0x84
#define BR_REQUEST_SET_CUR 0x01
#define BR_REQUEST_SET_MIN 0x02
#define BR_REQUEST_SET_MAX 0x03
#define BR_REQUEST_SET_RES 0x04
With a debug terminal in place it's clear Win7 connects to the Device
with a sequence of get_cur_mute, get_cur_volume, get_min, get_max,
get_res, get_cur_volume, get_min, get_max, get_res, set_res,
set_cur_vol, set_cur_vol etc. From what I can see in the debug
terminal the Device seems to be outputting reasonable values.
Importantly, Windows doesn't attempt any set_min, set_max or set_res.
When I pull the volume slide up and down in Windows there is no
get_cur, only a lot of set_cur_volume with a parameter stuck at
0x0000. Pulling the slide in Linux produces a lot of set_cur_volume
with a variable parameter. For each volume change with the button of
an iPhone, iOS performs a sequence of get_min, get_res,
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