sound distortion

[Haines Brown]

I installed on Debian Wheezy (3.2.0-4-686-pae #1 SMP Debian
3.2.65-1 i686 GNU/Linux) an Asus Xonar DS PCI Express 7.1. It
played beautifully out of the box, but next day it played with
much distortion. I believe the only thing I did after the initial
success was to remove a line in /etc/modprobe.d/alsa/alsa-base.config
with which I tried to 
correct an old card priority problem.

Sound is hopeless distorted. When I play a CD disk with
alsaplayer the sound stutters: sometimes sound amplitude seems
modulated by a sinewave at about 8Hz/sec and sometimes it
stutters or is silent. What I find significant is that when
alsaplayer is stopped, the stuttering continues for a second or
two longer. Does this suggest feedback?

When I play a .wav file with aplay, the sound is a screech. I
installed pulseaudio and it produced no sound at all and so
removed it. Nevertheless pulse shows up:

  $ aplay -L
  null
      Discard all samples (playback) or generate zero samples (capture)
  pulse
      PulseAudio Sound Server
  default:CARD=DX
      Xonar DX, Multichannel
      Default Audio Device
  sysdefault:CARD=DX
      Xonar DX, Multichannel
      Default Audio Device
  front:CARD=DX,DEV=0
      Xonar DX, Multichannel
      Front speakers
  ...

The driver for the card is snd_virtuoso:

    # lspci -v
    06:04.0 Multimedia audio controller: C-Media Electronics Inc CMI8788 \
            [Oxygen HD Audio]
    Subsystem: ASUSTeK Computer Inc. Virtuoso 100 (Xonar DX)
    Flags: bus master, medium devsel, latency 32, IRQ 19
    I/O ports at d000 [size=256]
    Capabilities: <access denied>
    Kernel driver in use: snd_virtuoso

Nothing about the card or driver loading is reported by $
dmesg. This perhaps because its earlier portion was overwritten
by subsequent garbage, multiple repititions of:

    sr 4:0:0:0: [sr0]  Sense Key : Illegal Request [current]
    ILI
    sr 4:0:0:0: [sr0]  Add. Sense: Illegal mode for this track
    sr 4:0:0:0: [sr0] CDB: Read(10): 28 00 00 00 00 00 00 00 02 00
    end_request: I/O error, dev sr0, sector 0
    sr 4:0:0:0: [sr0]  Result: hostbyte=DID_OK driverbyte=DRIVER_SENSE

 However, that garbage ended and for a day I've not seen any more of it.
 So in place of dmesg I turn to /var/log/boot. A | grep snd returns:

  Thu Feb 12 14:23:18 2015: Loading kernel module snd-ctxfi.

This is strange. Last week I tried to install an Audigi X-Fi
Titanium before I relized it is not supported by Debian. This
snd-ctxfi sounds like its module is loaded for some reason.

  # lsmod
  ...
  snd_ctxfi              62598  0
  ...
  snd_hda_codec_hdmi     26352  1
  snd_virtuoso           33765  2
  snd_oxygen_lib         27905  1 snd_virtuoso
  snd_mpu401_uart        13299  1 snd_oxygen_lib
  snd_usb_audio          71436  0
  snd_usbmidi_lib        18801  1 snd_usb_audio
  snd_seq_midi           12744  0
  snd_seq_midi_event     13124  1 snd_seq_midi
  snd_rawmidi            22472  3 \
    snd_seq_midi,snd_usbmidi_lib,snd_mpu401_uart
  ...
  snd_hda_intel          21786  1
  snd_hda_codec          63477  2 snd_hda_intel,snd_hda_codec_hdmi
  ...
  snd_hwdep              12943  2 snd_hda_codec,snd_usb_audio
  snd_pcm                53461  7 \
  snd_hda_codec,snd_hda_intel,snd_usb_audio,\
    snd_oxygen_lib,snd_hda_codec_hdmi,snd_ctxfi
  ...
  snd_page_alloc         12867  3 snd_pcm,snd_hda_intel,snd_ctxfi
  ...
  snd_seq                39512  2 snd_seq_midi_event,snd_seq_midi
  snd_seq_device         13016  3 snd_seq,snd_rawmidi,snd_seq_midi
  snd_timer
  ...
  snd                    42761  19
    snd_timer,snd_seq_device,snd_seq,snd_pcm,snd_hwdep,snd_hda_codec,\
    snd_hda_intel,snd_rawmidi,snd_usbmidi_lib,snd_usb_audio, \
    snd_mpu401_uart,snd_oxygen_lib,snd_virtuoso,snd_hda_codec_hdmi,\
    snd_ctxfi

Don't know if this could be a problem, so unloaded it and
restarted alsa-utils. That had no effect on the problem.