Entry
The interesting part of a biosignal system is rarely only the final classifier. The real work starts earlier, at the layer where electrode contact, cable routing, grounding, shielding, synchronization, and physical comfort decide whether the data is usable at all.
Working on an EEG/EMG helmet makes that obvious very quickly. Small mechanical choices change the noise floor. Convenience features become signal-quality decisions. A design that looks elegant in a block diagram can become unmaintainable the moment a person has to wear it for a full session.
That is why I treat hardware, firmware, and analysis as one system. Acquisition quality constrains the models you can train, the features you can trust, and the experiments you can repeat. A poor interface upstream creates ambiguity all the way down the pipeline.
The payoff is that once the physical system is disciplined, the modeling questions become cleaner. You can spend more time on dynamics, stability, and interpretation, and less time guessing whether a result is just a wiring artifact.