Which of the following is not useful in digital EEG recordings?

Bio calibration is not typically considered useful in the context of digital EEG recordings because it primarily relates to establishing a baseline measurement of a biological system, which is more relevant to analog systems. In digital EEG recordings, the focus is on the clarity and accuracy of the digital data being collected, rather than baseline calibration of instrumental equipment.

Digital EEG techniques emphasize the importance of system reference, which helps in noise reduction and improves signal quality, as it allows for a comparative reference point for the signals being recorded. The balance of electrode imbalances is crucial in ensuring that the recorded signals accurately represent the brain's electrical activity, minimizing artifacts from uneven electrode impedances. Filters are integral to digital EEG as they help to eliminate unwanted frequency noise and enhance signal quality, allowing for clearer analysis of brain activity.

Each of these elements plays a vital role in enhancing the performance and reliability of digital EEG systems, making bio calibration less relevant in this specific context.