1 ===================== 1 =====================
2 Audio Pops and Clicks 2 Audio Pops and Clicks
3 ===================== 3 =====================
4 4
5 Pops and clicks are unwanted audio artifacts c 5 Pops and clicks are unwanted audio artifacts caused by the powering up and down
6 of components within the audio subsystem. This 6 of components within the audio subsystem. This is noticeable on PCs when an
7 audio module is either loaded or unloaded (at 7 audio module is either loaded or unloaded (at module load time the sound card is
8 powered up and causes a popping noise on the s 8 powered up and causes a popping noise on the speakers).
9 9
10 Pops and clicks can be more frequent on portab 10 Pops and clicks can be more frequent on portable systems with DAPM. This is
11 because the components within the subsystem ar 11 because the components within the subsystem are being dynamically powered
12 depending on the audio usage and this can subs 12 depending on the audio usage and this can subsequently cause a small pop or
13 click every time a component power state is ch 13 click every time a component power state is changed.
14 14
15 15
16 Minimising Playback Pops and Clicks 16 Minimising Playback Pops and Clicks
17 =================================== 17 ===================================
18 18
19 Playback pops in portable audio subsystems can 19 Playback pops in portable audio subsystems cannot be completely eliminated
20 currently, however future audio codec hardware 20 currently, however future audio codec hardware will have better pop and click
21 suppression. Pops can be reduced within playb 21 suppression. Pops can be reduced within playback by powering the audio
22 components in a specific order. This order is 22 components in a specific order. This order is different for startup and
23 shutdown and follows some basic rules:- 23 shutdown and follows some basic rules:-
24 :: 24 ::
25 25
26 Startup Order :- DAC --> Mixers --> Output 26 Startup Order :- DAC --> Mixers --> Output PGA --> Digital Unmute
27 27
28 Shutdown Order :- Digital Mute --> Output P 28 Shutdown Order :- Digital Mute --> Output PGA --> Mixers --> DAC
29 29
30 This assumes that the codec PCM output path fr 30 This assumes that the codec PCM output path from the DAC is via a mixer and then
31 a PGA (programmable gain amplifier) before bei 31 a PGA (programmable gain amplifier) before being output to the speakers.
32 32
33 33
34 Minimising Capture Pops and Clicks 34 Minimising Capture Pops and Clicks
35 ================================== 35 ==================================
36 36
37 Capture artifacts are somewhat easier to get r 37 Capture artifacts are somewhat easier to get rid as we can delay activating the
38 ADC until all the pops have occurred. This fol 38 ADC until all the pops have occurred. This follows similar power rules to
39 playback in that components are powered in a s 39 playback in that components are powered in a sequence depending upon stream
40 startup or shutdown. 40 startup or shutdown.
41 :: 41 ::
42 42
43 Startup Order - Input PGA --> Mixers --> AD 43 Startup Order - Input PGA --> Mixers --> ADC
44 44
45 Shutdown Order - ADC --> Mixers --> Input P 45 Shutdown Order - ADC --> Mixers --> Input PGA
46 46
47 47
48 Zipper Noise 48 Zipper Noise
49 ============ 49 ============
50 An unwanted zipper noise can occur within the 50 An unwanted zipper noise can occur within the audio playback or capture stream
51 when a volume control is changed near its maxi 51 when a volume control is changed near its maximum gain value. The zipper noise
52 is heard when the gain increase or decrease ch 52 is heard when the gain increase or decrease changes the mean audio signal
53 amplitude too quickly. It can be minimised by 53 amplitude too quickly. It can be minimised by enabling the zero cross setting
54 for each volume control. The ZC forces the gai 54 for each volume control. The ZC forces the gain change to occur when the signal
55 crosses the zero amplitude line. 55 crosses the zero amplitude line.
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