This is a Magisk module to fix
Microphone quality of the FP4 when using Signal (low volume).
It simply overlays mixer_paths_lagoon_fp4.xml with a modified version.
The effective patch is
--- mixer_paths_lagoon_fp4.xml 2022-01-05 09:31:56.000000000 +0100
+++ mixer_paths_lagoon_fp4.xml.dec0_100 2022-01-08 09:10:08.000000000 +0100
@@ -3431,6 +3431,7 @@
<path name="handset-mic">
<ctl name="TX_CDC_DMA_TX_3 Channels" value="One" />
+ <ctl name="TX_DEC0 Volume" value="100" />
<path name="amic1" />
</path>
This modification will let the HAL raise ALSA control "TX_DEC0 Volume" from 81to 100
whenever a recording with input device set to "handset-mic" happens and take it back afterwards.
Original file was sampled from A.094.20211213. Be careful when applying to newer FP4 versions.
If they changed mixer_paths_lagoon_fp4.xml, you would still see the old sampled version.
Eventually the issue should be fixed by Fairphone in their stock ROM, rather than in a community reverse engineering attempt. Please consider opening a request at support.fairphone.com to raise importance.
The low volume bug happens because FP4's audio HAL sets up the bottom microphone for audio recordings just like it would during a regular phone call. That doesn't make sense:
- during a regular phone call, we're typically 10 cm or closer to the bottom mic
- during a audio recording we're likely more distant, say 0.5 m to 5 m
Because p ~ 1/r, a much lower signal is to be expected in the audio recording case.
To get a reasonable recording level anyway one can e.g. increase gain, or route the audio input to
signal processing stages like AGC or
compressor.
To reason about bug and fix, we need some understanding of the FP4's audio stack. It's roughly like below. No warranty, I've no access to restriced Qualcomm material and just combined public sources and findings from debugging sessions.
+---------------+
| recording app |
+---------------+
| import android.media.MediaRecorder
+-------------------------+
| Android Media Framework |
+-------------------------+
| Binder IPC
+-------------------------+
| AudioFlinger |
| inside mediaserver |
+-------------------------+
| load library
+-----------------------------+
| Qualcomm specific audio HAL | --- /vendor/etc/audio_platform_info_lagoon_fp4.xml,
| audio.primary.lito.so | mixer_paths_lagoon_fp4.xml, ...
+-----------------------------+
| load library | load library
+----------------+ +------------------+
| tinyalsa | | ACDB Loader | --- /vendor/etc/acdbdata/*/*.acdb
| libtinyalsa.so | | proprietary |
+----------------+ | libacdbloader.so |
| +------------------+
| ioctl, mmap | ioctl
| 34 PCM devices |
| 3189 controls |
___________________________________
| Linux kernel 4.19 | --- Device Tree Blob and Overlay,
| | including qcom,msm-audio-apr subtree
| Out-of-tree ALSA SoC layer driver | handed over by bootloader
| kona.c, module_platform_driver( |
| kona_asoc_machine_driver); |
|___________________________________| _____________
| runs on | QuRT OS |
| | proprietary |
| |_____________|
| | runs on
____|____________________________________|____
| | Qualcomm Snapdragon 750G SoC | |
| | aka SM7225 Mobile Platform | |
| | | |
| +----------------+ | |
| | CPU Kryo 570 | | |
| | Cortex-A77/A55 | | |
| +----------------+ | |
| +--------------------+ +-----------------+ |
| | Audio Codec WX938x | | DSP Hexagon 694 | |
| +--------------------+ +-----------------+ |
|__|_____|_____|_______________________________|
| | |
MEMS MEMS MEMS
Mic1 Mic2 Mic3
References: