Bias adjustment on a two head cassettedeck

A cassette deck is factory adjusted to give a flat frequency response for the different tape types it supports. This is mainly done by the internal settings record/playback equalizing and bias. On the front is a often a knob called "fine bias". With this you are able to fine tune the frequency response for the specific tape you are using. When high and low frequency response are not equal do the following. Increase bias to reduce high frequencies. Or reduce bias to increase high frequencies.

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