Merge branch 'linus' of master.kernel.org:/pub/scm/linux/kernel/git/perex/alsa

* 'linus' of master.kernel.org:/pub/scm/linux/kernel/git/perex/alsa: (212 commits)
  [PATCH] Fix breakage with CONFIG_SYSFS_DEPRECATED
  [ALSA] version 1.0.14rc2
  [ALSA] ASoC documentation updates
  [ALSA] ca0106 - Add missing sysfs device assignment
  [ALSA] aoa i2sbus: Stop Apple i2s DMA gracefully
  [ALSA] hda-codec - Add support for Fujitsu PI1556 Realtek ALC880
  [ALSA] aoa: remove suspend/resume printks
  [ALSA] Fix possible deadlocks in sequencer at removal of ports
  [ALSA] emu10k1 - Fix STAC9758 front channel
  [ALSA] soc - Clean up with kmemdup()
  [ALSA] snd-ak4114: Fix two array overflows
  [ALSA] ac97_bus power management
  [ALSA] usbaudio - Add support for Edirol UA-101
  [ALSA] hda-codec - Add ALC861VD/ALC660VD support
  [ALSA] soc - ASoC 0.13 Sharp poodle machine
  [ALSA] soc - ASoC 0.13 Sharp tosa machine
  [ALSA] soc - ASoC 0.13 spitz machine
  [ALSA] soc - ASoC Sharp corgi machine
  [ALSA] soc - ASoC 0.13 pxa2xx DMA
  [ALSA] soc - ASoC 0.13 pxa2xx AC97 driver
  ...

1 files changed, 52 insertions, 0 deletions

diff --git a/Documentation/sound/alsa/soc/pops_clicks.txt b/Documentation/sound/alsa/soc/pops_clicks.txt
new file mode 100644
index 00000000000..2cf7ee5b3d7
--- /dev/null
+++ b/Documentation/sound/alsa/soc/pops_clicks.txt
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+Audio Pops and Clicks
+=====================
+
+Pops and clicks are unwanted audio artifacts caused by the powering up and down
+of components within the audio subsystem. This is noticable on PC's when an
+audio module is either loaded or unloaded (at module load time the sound card is
+powered up and causes a popping noise on the speakers).
+
+Pops and clicks can be more frequent on portable systems with DAPM. This is
+because the components within the subsystem are being dynamically powered
+depending on the audio usage and this can subsequently cause a small pop or
+click every time a component power state is changed.
+
+
+Minimising Playback Pops and Clicks
+===================================
+
+Playback pops in portable audio subsystems cannot be completely eliminated atm,
+however future audio codec hardware will have better pop and click supression.
+Pops can be reduced within playback by powering the audio components in a
+specific order. This order is different for startup and shutdown and follows
+some basic rules:-
+
+ Startup Order :- DAC --> Mixers --> Output PGA --> Digital Unmute
+
+ Shutdown Order :- Digital Mute --> Output PGA --> Mixers --> DAC
+
+This assumes that the codec PCM output path from the DAC is via a mixer and then
+a PGA (programmable gain amplifier) before being output to the speakers.
+
+
+Minimising Capture Pops and Clicks
+==================================
+
+Capture artifacts are somewhat easier to get rid as we can delay activating the
+ADC until all the pops have occured. This follows similar power rules to
+playback in that components are powered in a sequence depending upon stream
+startup or shutdown.
+
+ Startup Order - Input PGA --> Mixers --> ADC
+
+ Shutdown Order - ADC --> Mixers --> Input PGA
+
+
+Zipper Noise
+============
+An unwanted zipper noise can occur within the audio playback or capture stream
+when a volume control is changed near its maximum gain value. The zipper noise
+is heard when the gain increase or decrease changes the mean audio signal
+amplitude too quickly. It can be minimised by enabling the zero cross setting
+for each volume control. The ZC forces the gain change to occur when the signal
+crosses the zero amplitude line.