Hum Bug Reference Manual Page 3
Quest Scientific
INTRODUCTION
This manual describes the operation, connections and normal use of the Hum Bug in the
neurosciences and related fields of research. The original Hum Bug was developed in the
electrophysiology laboratory of Dr. Tom Richardson in response to problems with electrical
interference during intracellular studies. In theory, proper attention to grounding and appropriate
shielding can eliminate 50/60
1
Hz noise induced by electrical wiring, power supplies, and lights.
In practice, this noise remains a frequent and distressing problem in the daily operation of many
electrophysiology laboratories. Even with diligent attention to detail, noise may come and go for
no apparent reason and may appear during critical phases of data collection. The effort required
to maintain noise at an acceptable level is time consuming and frustrating.
Notch
or
Comb
filters are sometimes used to attenuate 50/60 Hz noise and related
harmonics. Unfortunately, the composition of many biological signals includes these
frequencies. As a result, critical components of the signal are filtered along with the noise. This
distortion and loss of information is usually unacceptable for scientific investigation.
The Hum Bug is a simple and hassle free solution to these problems. It will eliminate
electrical interference from physiological recordings without altering your signal of interest.
Simply insert it into the signal path of your recording system and it will automatically eliminate
noise without any need for adjustment.
The Hum Bug is not a filter. It is a new
class
of instrument capable of eliminating
electrical interference from analogue signals without creating phase shifts, frequency loss,
amplitude errors, DC shifts, time delays, or digital distortion. It effectively eliminates 50/60 Hz
2
noise and harmonics
3
without altering the frequency characteristics of the desired signal
4
even
when frequencies within the signal overlap with noise components. It uses an advanced signal
processing circuit to continuously construct a replica of noise present on the input and to subtract
this replica from the original signal. The end result is a clean signal which is free from
distortion. It performs this function in the presence of biological activity even when the shape,
amplitude, and harmonic content of the noise evolves over time.
The Hum Bug can eliminate 50/60 Hz noise from virtually any analogue signal. It is
equally effective at removing noise associated with inadequate grounding, ground loops, and
electrical pickup. Common applications include noise elimination from signals recorded using
microelectrodes, skin electrodes (EKG, EMG, EEG), high gain amplifiers, magnetic sensors, and
audio equipment.
1
The frequency depends on the AC frequency of the power mains. This frequency is 60 Hz in North America and
50 Hz in many other regions of the world.
2
Each Hum Bug is internally configured for either a 50 or 60 Hz fundamental.
3
Electrical interference is usually composed of a variety of frequencies which are harmonics of the 50/60 Hz
fundamental. Frequencies as high as 1 kHz are not uncommon. The Hum Bug will eliminate harmonics with
frequencies up to 4 kHz.
4
For frequencies up to at least 500 kHz