analog filtering vs digital filtering?

Question

Dear All,
I would like to ask, why are companies still using analog filters. All the filtering can easily be done by digital filtering. Why is the need of analog filters still necessary. All the filtering can be done by digital filters.
I want to eliminate 50Hz noise from EEG. Cant I just record the signal and eliminate 50Hz noise. Is a filter implemented in hardware better?
why should I use analog filters when I can use digital filters. And any way I have more options when using digital filtering and I do not loose the neighboring frequencies, in a band stop filter when I use digital filters.
thank you.
Munir Afzal Bhatti

Answer 1

Consider signals that have energy at frequencies higher than the Nyquist sampling frequency of your system. Some of those may be aliased as 50 Hz signals, and once sampled you could not tell them apart from 'real' 50 Hz signals. Granted, you wish to filter out all 50 Hz noise no matter the source, but consider aliased 70 Hz noise that now masquerades as a real EEG signal -- how do you separated the real EEG from the aliased high frequency noise generated EEG? You cannot separate aliased signals from real signals in a digital system, once the aliased noise has been sampled.

The *only* option for an anti-aliasing filter on a sampling (digital) system is an analog filter in "front" of the ADC.

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Answer 2

There are reasons for using both. You need to know the characteristics of your problem before you can select. For example the power.

For signal processing, digital filtering may be best, but you can't filter a power supply output using a computer.

Answer 3

For an analog filter, you may get by with just a f few discrete components. I digital filter requires a DSP and someone to program it and something to power it. An analog filter is cheap and uses no power.

Answer 4

All pictures is analog till the Analog to digital Converter does its artwork interior your digicam. in my opinion i've got grown particularly weary of comparing movie based pictures to digital pictures. on the tip of the day all that fairly concerns is the flexibility of the photographer to apply their expertise of sunshine, composition, exposure and intensity of field to make the image they have the prefer to make.