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Combating electrical hum with HumSilencer technology

Electrical hum is the most common source of background noise in electrophysiology experiments. It is unwanted electrical activity detected by your recording equipment, which interferes with or hides the activity you are trying to measure. Electrical hum is caused by the alternating current of the electrical grid, which interferes with biological signals. Hum occurs not only at the powerline frequency (usually 50 or 60 Hz, determined by mains power) but also for high-frequency harmonics.

Eliminating background noise from the final output is one of the largest and most constant challenges to electrophysiologists, especially when fine recordings are being made. For example, single channel recordings used to explore individual ion channels can be overwhelmed by high levels of background noise.

Scientifica’s electrophysiology systems have internal shielding and high-quality motors that ensure minimal (or zero) noise. However, electrical noise can originate from almost any electronic device, within or outside of the lab. Ensuring your rig is properly grounded will also ensure there is minimal noise picked up in your recording.  

Reducing electrical hum

To reduce electrical noise, including hum, in systems researchers often use homespun approaches, such as wrapping up electrophysiology system components and possible sources of electrical noise in aluminium foil. However, this approach is becoming less common due to it being unlikely to fully eliminate electrical noise and can carry the risk of introducing additional noise to the system.

There are more reliable noise reduction technologies on the market that are becoming increasingly used by researchers, including the HumSilencer™ Adaptive Noise Cancellation system from Molecular Devices. 

Read our popular #LabHacks guide on how to reduce the noise around your electrophysiology rig

What is the HumSilencer?

The HumSilencer feature is integrated into the Molecular Devices Axon™ Digidata® 1550B Low-Noise Data Acquisition System. This is a high-resolution, low-noise digitizer intended for precision scientific applications. It is particularly designed for electrophysiology experiments, to send and receive signals from microelectrode amplifiers, and to interact with peripheral instruments such as solution changers and stimulators.

The HumSilencer Adaptive Noise Cancellation system uses a combination of analogue signal-processing circuitry and high-speed computing hardware to learn and subtract out unwanted electrical hum. As electrical hum is predictable and occurs at regular frequencies, the HumSilencer technology can distinguish between noise caused by electrical hum and other signals. By creating a rolling average over time, the HumSilencer can subtract the electrical hum from the signal. It takes approximately a second to subtract unwanted electrical hum from the final output and can be turned on or off with a single mouse-click in Axon pCLAMP™ software.

Figure 1: HumSilencer (HS) enables accurate signal measurement in single-channel recordings (HumSilencer-subtracted data in top panel, raw data in bottom panel). Single-channel recording of the principal subunit of the olfactory cyclic nucleotide-gated channel (CNCA2). The excised membrane patch was isolated from HEK293 cells transfected with CNCA2, and the membrane clamped at +50 mV in the presence of 1 μM cGMP. Data courtesy of Tsung-Yu Chen, Ph.D., University of California, Davis.

This approach ensures that the acquired signal is not lost, distorted or attenuated. The result is a cleaner signal, with less interference from electrical noise, and better results.

The Digidata hardware is available with up to four individual channels with the HumSilencer technology.

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