53 lines
2.1 KiB
Plaintext
53 lines
2.1 KiB
Plaintext
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.
|