I see in V1.1beta2 (Release date: 2016-07-20) the following guidance on Volume Control for the Apalis:
Description: Currently the audio driver uses only the main volume setting on the external audio chip to configure output volume, this leads to a low volume on the headset output used as audio output on the modules. The volume can be increase by setting the “HPVolume” dword value under [HKEY_LOCAL_MACHINE\Drivers\Builtin\Audio] to a value between 0 and 255. Increasing this volume above a certain value can lead to distortion on the output, depending on the configuration of the carrier board and speakers.
We’ve been trying different settings for HPVolume and we aren’t finding a linear relationship between the setting and the perceived audio coming out of the speaker. Here’s what we found:
HPVolume setting Dec Hex Perception 255 FF lowest 254 fe lowest 196 C4 med-low 143 8F med-high 129 81 loudest 128 80 loudest 127 7F silent 120 78 low 64 40 med-low 1 1 loudest 0 0 lowest
I imagine that this registry setting is read and then used to set the CHIP_ANA_HP_CTRL 0x0022 register in the SGTL5000 CODEC. That’s a 16 bit register with 2 reserved bits. How does the 8 bit HPVolume setting used to set this register? Or is there something else going on?