162306a36Sopenharmony_ci===================== 262306a36Sopenharmony_ciAudio Pops and Clicks 362306a36Sopenharmony_ci===================== 462306a36Sopenharmony_ci 562306a36Sopenharmony_ciPops and clicks are unwanted audio artifacts caused by the powering up and down 662306a36Sopenharmony_ciof components within the audio subsystem. This is noticeable on PCs when an 762306a36Sopenharmony_ciaudio module is either loaded or unloaded (at module load time the sound card is 862306a36Sopenharmony_cipowered up and causes a popping noise on the speakers). 962306a36Sopenharmony_ci 1062306a36Sopenharmony_ciPops and clicks can be more frequent on portable systems with DAPM. This is 1162306a36Sopenharmony_cibecause the components within the subsystem are being dynamically powered 1262306a36Sopenharmony_cidepending on the audio usage and this can subsequently cause a small pop or 1362306a36Sopenharmony_ciclick every time a component power state is changed. 1462306a36Sopenharmony_ci 1562306a36Sopenharmony_ci 1662306a36Sopenharmony_ciMinimising Playback Pops and Clicks 1762306a36Sopenharmony_ci=================================== 1862306a36Sopenharmony_ci 1962306a36Sopenharmony_ciPlayback pops in portable audio subsystems cannot be completely eliminated 2062306a36Sopenharmony_cicurrently, however future audio codec hardware will have better pop and click 2162306a36Sopenharmony_cisuppression. Pops can be reduced within playback by powering the audio 2262306a36Sopenharmony_cicomponents in a specific order. This order is different for startup and 2362306a36Sopenharmony_cishutdown and follows some basic rules:- 2462306a36Sopenharmony_ci:: 2562306a36Sopenharmony_ci 2662306a36Sopenharmony_ci Startup Order :- DAC --> Mixers --> Output PGA --> Digital Unmute 2762306a36Sopenharmony_ci 2862306a36Sopenharmony_ci Shutdown Order :- Digital Mute --> Output PGA --> Mixers --> DAC 2962306a36Sopenharmony_ci 3062306a36Sopenharmony_ciThis assumes that the codec PCM output path from the DAC is via a mixer and then 3162306a36Sopenharmony_cia PGA (programmable gain amplifier) before being output to the speakers. 3262306a36Sopenharmony_ci 3362306a36Sopenharmony_ci 3462306a36Sopenharmony_ciMinimising Capture Pops and Clicks 3562306a36Sopenharmony_ci================================== 3662306a36Sopenharmony_ci 3762306a36Sopenharmony_ciCapture artifacts are somewhat easier to get rid as we can delay activating the 3862306a36Sopenharmony_ciADC until all the pops have occurred. This follows similar power rules to 3962306a36Sopenharmony_ciplayback in that components are powered in a sequence depending upon stream 4062306a36Sopenharmony_cistartup or shutdown. 4162306a36Sopenharmony_ci:: 4262306a36Sopenharmony_ci 4362306a36Sopenharmony_ci Startup Order - Input PGA --> Mixers --> ADC 4462306a36Sopenharmony_ci 4562306a36Sopenharmony_ci Shutdown Order - ADC --> Mixers --> Input PGA 4662306a36Sopenharmony_ci 4762306a36Sopenharmony_ci 4862306a36Sopenharmony_ciZipper Noise 4962306a36Sopenharmony_ci============ 5062306a36Sopenharmony_ciAn unwanted zipper noise can occur within the audio playback or capture stream 5162306a36Sopenharmony_ciwhen a volume control is changed near its maximum gain value. The zipper noise 5262306a36Sopenharmony_ciis heard when the gain increase or decrease changes the mean audio signal 5362306a36Sopenharmony_ciamplitude too quickly. It can be minimised by enabling the zero cross setting 5462306a36Sopenharmony_cifor each volume control. The ZC forces the gain change to occur when the signal 5562306a36Sopenharmony_cicrosses the zero amplitude line. 56