Is it possible to reduce the hardware filters associated with ADInstruments’ bio-amplifiers?

Bio amplifiers supplied by ADInstruments, including ones associated with teaching PowerLabs, have pre-defined hardware high-pass & low-pass filters (HPF/LPF).This allows users to change filters and allow certain signal frequencies to be seen.In most cases these ranges are fine, but they may not be suitable for all applications.

There may be circumstances where these HPF don’t go low enough.You should first choose the most appropriate amplifier as they have different specifications.Alternatively, you can alter these, hardware HPF, with a “digital filter” using the Arithmetic function.

Some applications may need a very low, HPF (<0.001Hz) to acquire very slow osculating signals.This type of signal is common after traumatic brain injury which is often looked at by neuro researchers.These signals will be removed with the standard amplifier/software filter settings.

The document found here explains this in detail and has been developed from techniques described here, while the resultant LabChart signals can be seen here.

Simply; the Arithmetic function is used to reduce the distortion of AC coupled waveforms by applying a digital filter which approximates the inverse of the Bio Amp analogue High Pass Filter (HPF) used to perform the AC coupling. The resulting recorded waveform appears as if it was recorded using a HPF with a cut off frequency much lower than the analogue filter actually used.