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Diffstat (limited to 'Documentation/sound/alsa/soc/pops_clicks.txt')
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diff --git a/Documentation/sound/alsa/soc/pops_clicks.txt b/Documentation/sound/alsa/soc/pops_clicks.txt new file mode 100644 index 0000000..f4f8de5 --- /dev/null +++ b/Documentation/sound/alsa/soc/pops_clicks.txt @@ -0,0 +1,52 @@ +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. |