The NEW D400 Multi-channel 50Hz/60Hz Mains Noise Eliminator is a standalone instrument designed for real-time removal of 50Hz or 60Hz mains noise interference, including harmonics, from amplified biological and other signals prior to acquisition by digital data recording systems. Unlike 50Hz/60Hz notch filters, the D400 noise eliminator can remove mains noise without degrading the signal of interest, even if it overlaps with the mains frequency.
Rapidly evolving multi-channel mains noise removal
The D400 is unique as a multi-channel, standalone mains noise eliminator, which is not incoporated within and does not have to be used in conjunction with any specific electrophysiology data acquisition system. While the method of noise removal follows the principles of other single channel devices, such as the Humbug Noise Eliminator, the hardware and software algorithms used by the D400 have been developed wholly by Digitimer and are unique to this device. For those unfamiliar with the concept of operation, the D400 receives amplified analogue voltage signals (AC or DC coupled) from an amplifier via its inputs and as these signals pass through the D400 noise eliminator remaining in the analogue domain, it rapidly constructs a phase-locked “mains noise template” and subtracts this from the original signal. Noise removal occurs in real-time and the noise template evolves constantly, so that any changes in the amplitude or other characteristics of the noise are corrected for.
The Digitimer D400 is NOT a mains noise filter, making this the main reason it is a special, and unique as a standalone multi-channel device. Filtering often results in phase shifts, frequency loss, amplitude errors, DC shifts, time delays or digital distortion, but the D400 will eliminate 50/60Hz electrical interference (and harmonics) without altering your signal of interest.
No, absolutely not. This is one of the key features of active noise cancellation devices, in that they syncronise with the local mains frequency whether it is 50Hz or 60Hz and will ignore components of the input waveform even if they overlap with these mains frequencies. As a result, many researchers interested in signals within the gamma band will opt for devices like the D400.
The D400 adapts rapidly when the input signal is dominated by noise and proceeds more slowly when low amplitude noise is embedded within continuous physiological activity. Adaptation is also slower for harmonics with frequencies greater than 1kHz.
No, the D400 has a distinct noise template for each channel. This means that it is theoretically possible to share one D400 across more than one electrophysiology rig, although there may be issues when any of the function buttons need to be used, as their actions are applied globally to all channels.
The obvious benefit is that the user can control the D400 without having to look away from or move from their computer screen when using the clear, hold or bypass controls. However, the other advantage is that individual channels can be controlled separately from the software. This may be of use in a rig that has 4 parallel brain slice recordings and the operator only wants to make adjustments to one of them, without affecting the other electrophysiological recordings.
The D400 software also allows the user to visualise the noise template rather than the cleaned output signal, in order to verify exactly what is being subtracted from the amplified signal of interest.
The Windows GUI is intended to be used in situations where the user cannot reach the D400 front panel or if they want to control the D400 on a per channel basis. If preferred, the D400 can be used as a standalone device without the USB connection or software control.