Dragonfly USB DAC under 9.1-RELEASE

[Craig Leres]

Has anybody tried a Dragonfly USB DAC with FreeBSD 9.1-RELEASE? I picked
up one last week can't quite get it to work

My streamer is a Barix instreamer. I normally feed it with 48 KHz PCM
from a Sirius Satellite radio receiver via toslink. I can also feed it
directly with 44.1 KHz from VBR MP3s downloaded from amazon.com or 48
KHz RIFF/WAVE files.

I'm using the multimedia/xmms port with the OSS plugin. I use mpg123 to
play MP3s. I think it uses OSS too. And obviously ossplay uses OSS.

The DACs I have previously used are Realtek ALC883 and ALC888's on the
motherboard of my desktop machines. With the Dragonfly plugged in,
/dev/sndstat says:

    ice 327 % cat /dev/sndstat
    FreeBSD Audio Driver (newpcm: 64bit 2009061500/amd64)
    Installed devices:
    pcm0: <ATI R6xx (HDMI)> on hdaa0  (1p:1v/0r:0v)
    pcm1: <Realtek ALC883 (Analog 7.1+HP/2.0)> on hdaa1  (1p:2v/2r:1v)
default
    pcm2: <USB audio> at ?  (1p:1v/0r:0v)

(The Dragonfly is pcm2.)

The first issue was a pop every 5 seconds. I noticed the LED was magenta
which indicated the DAC was running at 96K so I looked at
/sys/dev/sound/usb/uaudio.c and found that thd driver was defaulting to
the highest sample rate the DAC reports. This meant my 48K input source
was being upsampled.

Looking at the driver a bit more I changed:

    sysctl hw.usb.uaudio.default_rate=48000

and removed/inserted the DAC and that fixes it at 48K (confirmed by a
blue LED) and the 5 second pops are gone.

Now I have noticeable audio glitches about ever minute or so. I don't
think it's source material related. For example, if I play the same
sound file over and over and note the number of seconds into the song
when a glitch happens, it rarely happens at the same time.

I tried to attach a short wav file of an example glitch but got a funny
bounce ("550 5.7.1 Size too green"?) so I put a copy here:

    http://xse.com/leres/scratch/glitch.wav

Thinking it might be a ground loop problem, I got an Olimex USB-ISO USB
isolator. It works ok but the glitches are still present.

The Dragonfly sounds very nice so I hate to send it back; does anyone
have suggestions for me? I called Audio Quest but the tech I talked to
admitted he had only been trained for Windows and OSX.

		Craig