First of all it seems that the changes between the regular M8 and the M8 H&K Edition are only or mainly software related. We believe that the sound processor is the same in both units, however the firmware of that sound processor is probably different. To such conclusion led us the particular part of the M8 Sprint firmware.zip package called adsp.img (Advanced Digital Sound Processor) which is usually the same between each device variants and stays the same since the first device software release date, but in this case it was different. We found out that the adsp.img from the Sprint HTC One M8 was different to the others One M8 variants so it's probably needed for a proper H&K sound mod function.
The rest of the changes are located on /system partition:
- system/customize/ACC/default.xml
<item type="boolean" name="support_harman">false</item> has to be changed to
<item type="boolean" name="support_harman">true</item> to make the OS "think" that you're actually using the H&K M8 Edition. This boolean item wasn't present in the early HTC One M8 1.24.401.4 software version.
- system/etc/tfa/playbackHM.* / playbackHM_l.* files which are mostly related to the equalizer settings
- system/etc/audio_policy.conf tuned for higher sampling_rate values (up to 192000)
- system/lib and system/lib/hw libraries, mostly related to the part of the SoC responsible for the audio
This all might sound a little bit complicated, but in fact it was just an explanation about the changes that are required software-wise to enable the H&K support on the regular HTC One M8.
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