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