How do high pass and band filters work, why are they used and what are they used in?

Answer 1

High pass filters work by blocking low frequency signals and allowing high frequency signals to pass. An example in digital signal processing would be a simple difference filter: y[n] = x[n] - x[n-1]. If the input contained only low frequencies, such as x[n] = 5 for all n, then the output would be a constant 0 since the filter "blocks" low frequencies. However, if the input contained high frequencies (e.g. x[n] = (-1)^n), the output would have the same form as the input with a possibly different magnitude and phase (e.g. y[n] = 2*(-1)^n).

This type of operation is frequently used in image and video processing for edge detection. There, a fast transition from bright pixels to dark pixels or vice versa contains high frequencies that can be discovered using high pass filtering. Regions where the brightness is not changing will be suppressed. You could imagine such a system being used to detect certain shapes in an image such as faces for automatic recognition.

Answer 2

A high pass filter has a capacitor in series with the signal line and a resistor to the ground - not like the answer above.
It works because the impedance of the capacitor reduces with frequency, so high frequencies go through it, but low frequencies don't. The cut-off frequency is dependent on the values of C and R.

A low pass filter has the capacitor between signal and ground, and a resistor in series. The capacitor has a low impedance to high frequencies and thus shorts them to the ground.

A band pass filter is a combination of the two.

A filter with only one R and one C does not have a sharp cut-off frequency. To make it sharper, you have a whole sequence of Rs and Cs (in a 'passive filter') but in modern electronics you have an amplifier (transistor) with negative feedback to sharpen the filter.

Answer 3

To add to the previous answers, a crossover network in a loudspeaker system is likely to use a low-pass filter to feed the woofer, a high-pass filter for the tweeter, and a band-pass filter (which no-one has explained yet) to feed the squawker - or midrange speaker. A bandpass filter cuts off unwanted lower and higher frequencies to let only a "band" of desired frequencies through.

Answer 4

they use capacitance.

A capacitor from signal to ground with a series resistor will give you a high pass filter. Low frequencies will charge up the capacitor rather than go through the resistor

A capacitor is series with a resistor to ground will give you a low pass filter. Low frequencies will charge up the capacitor and the signal will be refleced on the other side of the capacitor.

A combination of the two will give you a band pass filter.

They are used to ensure erroneuos signals do not get through. I modern example is the dongle thing you put on your phone if you have broadband. It is a low pass fitler that stops the broadband high frequency getting through to your phone.

In realilty, virtually every elctronic circuit has some sort of pass filter.

Answer 5

A high pass circuit utilizes a capacitor.
A low pass circuit uses a coil.
In separating or blocking carrier waves.
The capacitor passes high frequency and blocks low frequency.
The coil blocks high frequency and passes low frequency.
They are used in combination's of certain values to select different frequencies for processing.
Usually in television circuits.