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Diffstat (limited to 'Documentation/sound/alsa/soc/pops_clicks.txt')
| -rw-r--r-- | Documentation/sound/alsa/soc/pops_clicks.txt | 52 |
1 files changed, 0 insertions, 52 deletions
diff --git a/Documentation/sound/alsa/soc/pops_clicks.txt b/Documentation/sound/alsa/soc/pops_clicks.txt deleted file mode 100644 index e1e74daa4497..000000000000 --- a/Documentation/sound/alsa/soc/pops_clicks.txt +++ /dev/null @@ -1,52 +0,0 @@ -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 noticeable on PCs 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 -currently, however future audio codec hardware will have better pop and click -suppression. 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 occurred. 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. |