How to suppress pop sound from HPH speaker

96boards

#1

I want to suppress pop sounds generated from HPH speakers at the end of audio output.
The HPH output has 500mV offset and the pop sound happens when it is turned off for power saving.
What is the easiest way to suppress the pop sounds?

Power consumption is not an issue.
I am working with DragonBoard 410c and Debian 17.09.


#2

The HPH speaker outputs have a 500mV offset because they are intended to drive a floating speaker, if you are using them single-ended you will hear a pop.

Since power consumption is not an issue for you, then I suggest that you simply leave it turned on all the time.

Full Disclosure: I am currently an employee of Qualcomm Canada and any opinions I may have left in this or any other post do not necessarily match the opinions of my employer. As of May 22nd/2018 I will no longer be employed by Qualcomm Canada. Currently looking for new opportunities, you can contact my personal email through the forums at 96Boards.


#3

Thanks for your suggestion.
Yes, I want to leave it turned on all the time, but still can’t find out how to do it.

My hardware configuration is:
An external power amp is used for loud speakers, and HPH_R/L outputs are connected to it with AC coupling via capacitors. HPH_REF and AGND are connected.
Is this configuration correct?


#4

Hi @Xen:

I had noticed the loud pop even with headphones attached to the headphone jack on the Audio Mezzanine board. I haven’t had a chance to go back and retest this with the Android build on the board, but I don’t remember this being a problem under Android.

I suspect that the Android builds do something different when powering up the headphone jack to avoid the pop noise. Maybe @srini or @nico in the Linaro team can take a look at this.

In the mean time, can you file a bug report on this at bugs.96boards.org so that the problem can be tracked through to a conclusion. Thanks.

Full Disclosure: I am no longer an employee of Qualcomm Canada and any opinions I may have left in this or any other post are my own. Currently looking for new opportunities, you can contact my personal email through the forums at 96Boards.


#5

Hi ljking,

Thanks for your suggestion.
I filed this issue as a bug report as Bug 736 on at bugs.96boards.org.