Yellow-gold dye media are the easiest to write but the least readable. Green dye media are somewhat harder to write and somewhat easier to read. Second, fields may be either induced into loops or dipoles, the effects of each type of field is different as are the remedies. Common mode v. differential mode and loop v. dipole are discussed below. Common mode voltage is that induced voltage present at both the plus and minus inputs of a channel referenced to ground.
Real amplifiers do pass common mode voltages.
60 Hz at the inputs can be minimized by dressing the ground lead close by the other electrode leads and choosing a ground site that is nearby all the other sites, e.g., AFz. The deleterious effects of common mode noise are specified by the amplifier manufacturer as a logarithmic ratio. CMRR also deteriorates with greater impedance mismatch between the plus and minus inputs, a specification rarely reported by bioamplifier manufacturers. 60 Hz is that induced voltage that presents a potential difference between the plus and minus inputs of a channel. Amplifier design can not change this voltage.