From eb1a6af39b70375d93ed25e7c916f64463e00614 Mon Sep 17 00:00:00 2001 From: Liam Girdwood Date: Fri, 6 Oct 2006 18:34:51 +0200 Subject: [ALSA] ASoC: documentation & maintainer This patch adds documentation describing the ASoC architecture and a maintainer entry for ASoC. The documentation includes the following files:- codec.txt: Codec driver internals. DAI.txt: Description of Digital Audio Interface standards and how to configure a DAI within your codec and CPU DAI drivers. dapm.txt: Dynamic Audio Power Management. platform.txt: Platform audio DMA and DAI. machine.txt: Machine driver internals. pop_clicks.txt: How to minimise audio artifacts. clocking.txt: ASoC clocking for best power performance. Signed-off-by: Liam Girdwood Signed-off-by: Takashi Iwai Signed-off-by: Jaroslav Kysela --- Documentation/sound/alsa/soc/pops_clicks.txt | 52 ++++++++++++++++++++++++++++ 1 file changed, 52 insertions(+) create mode 100644 Documentation/sound/alsa/soc/pops_clicks.txt (limited to 'Documentation/sound/alsa/soc/pops_clicks.txt') diff --git a/Documentation/sound/alsa/soc/pops_clicks.txt b/Documentation/sound/alsa/soc/pops_clicks.txt new file mode 100644 index 00000000000..f4f8de5a968 --- /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. -- cgit v1.2.3-70-g09d2