All transformers inherently behave as low-pass filters. The characteristics of a filter depends on its type or “alignment.” A Bessel filter is optimized for uniform time-domain response. This means all the overtones of a musical instrument stay properly time-aligned, preserving the instrument’s true timbre. In square-wave tests, a Bessel response is free of overshoot or ringing in the waveform. In frequency response plots, a Bessel response produces an unusually gradual high-frequency roll-off. All Jensen transformers are intentionally designed to have Bessel response curve.
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