How to filter ONE frequency or specified bandwidth?

[Vendrel]

Hi!

I'm just trying to cut every frequencies in a sample except 100 Hz (maybe 99-101 Hz or 98-102 Hz, that's okay) but the Equaliser always makes a curve (green spline on the screenshot below), causing remaining unwanted frequencies (noise, actually) in the sample.

Can this or another more appropriate function be set to not smooth the equalisation frequency map?

It could be great if there would be an effect providing a frequency cut. For example, using my case:
• Frequency: 100 Hz
• Bandwidth: 3 Hz
=> Result: every frequencies is muted below 99 Hz and above 101 Hz (this is that 3 Hz width)

In practice, of course, it would be also a solution if this green curve could be narrowed by a factor.

Thanks for the great work!

[kozikowski]

The black or blue line is the desire and the green line is what Audacity is actually going to do.

In the equalizer tool, the Length of Filter slider controls the steepness of the curve.

What's the goal? Frequencies are not a thing. A frequency is a rate of change and things don't go from dead zero to some frequency in no time. A filter may take a cycle or two of the event for it to even tell what the frequency is.

If you do get filter close, it may not do what you think it's going to do.

You cut off the left edge of the display. If the green spread is down in the -60dB and -70dB range, that's over a thousand times quieter than 0dB and can be ignored.

Why are we doing this?

Koz

[steve]

I'm just trying to cut every frequencies in a sample except 100 Hz (maybe 99-101 Hz or 98-102 Hz, that's okay)

There are many scientific and technical reasons why it is impossible to filter ONE frequency. However, you can get a fairly good approximation with the Equalization effect if you increase the filter "Size" to maximum.

Note that the steeper the filter slope, the more the filter will "ring". This ringing is common to all real-world filters, though some (such as the Equalization effect) are able to keep the amount of ringing reasonably small, even for very steep filters.
This image shows a single sample pulse that has been filtered with an extremely narrow filter at 2000 Hz:

First Track000.png (8.96 KiB) Viewed 434 times

[Trebor]

I'm just trying to cut every frequencies in a sample except 100 Hz (maybe 99-101 Hz or 98-102 Hz, that's okay) ...

Try this ultra-narrow plugin
(inevitably there will be ringing).