HaM5dsp - Another HW problem with M5Stack!
But with a quick fix!
Well, I wanted to have the input from the radio on the Tip of the 3.5mm TRS Jack.
This would be Left channel.
When Passthrough is selected, that should give a flat response (0 - 10 KHz); instead, a very strange octave filter was applied to the signal!
When the signal was on the Right channel (the Ring of the TRS connector) the audio response was absolutely flat!
After a day of trial and errors with all my M144 ES8388 Audio Module boards, I came to conclusion that ES8388 was, somehow, the result of a bad production run.
Untill I looked deep into the datasheet:
Can you see it?
Yup, that little “MIC_MONO_IN” is a circuit node and not a tag!
It goes directly into this multiplexer to let the microphone from the OUTPUT TRRS to go into the LEFT input from TRS connector!
Those components form a First‑order shelving (tilt) filter with approx. -6db at around 200 Hz and -17db above 500 Hz!
WTF???
WHY???
The solution is simple, albeit disturbing for my OCD: Line input on the Ring of the TRS Line Input.
