Help! 2000-5000 Hz filter

Hi!

I am a graduate student preparing to conduct a research project on emotional reactions to sounds. I need to filter 2000-5000 Hz frequency range from about 140 stimuli. Is there a way I can do this in the Audacity program? I have tried the band-stop plug in, but it doesn’t allow me to put in the upper and lower limit for filtering. Any help is MUCH appreciated!

Thanks!

The desperation method is:

Effect > High Pass Filter
Effect > Low Pass Filter

That will allow you to choose your high and low values and the cut-off slopes.

Try it once with Generate > Noise and then Analyze > Plot Spectrum to see if you get what you want.

I thought Effect > Notch Filter would do that, but it won’t. There’s Band Stop, but I don’t know we have a good pre-baked filter for that.

The values in the filters should stick and you only have to put them in once.

Koz

Thanks for the reply!

I have tried this by applying a low-pass of 2000Hz and a high-pass of 5000Hz. However, it doesn’t seem to actually be cutting out the frequency energy in the range between 2000 and 5000 Hz (as per the spectrogram and the plot spectrum analysis). When listening to the filtered vs. the original, they actually sound pretty much the same except the filtered stimuli sound quieter.

Any other input? I am a novice in this area so your help is very much appreciated!

I need to go play Real Life for a while. More later, or someone else may post.

You should know you are never going to get ruler-flat cuts and passes. Sound doesn’t work like that. You should choose the straightness and steepness of the active area in dB per octave, etc. etc.

For example, 3000Hz is not going to be dead, but it can be made to be 36dB quieter than 2000Hz.

As we go.

Koz

I need to filter 2000-5000 Hz frequency range

I guess you mean filter-out?

You can make a 2kHz low-passed file and a 5kHz high passed file, open them both in the same Audacity project and export to mix the two files.

Or, the Equalizer can cut by 30dB which might be enough for you.

In addition to what Koz said, the cutoff frequency of any filter (any slope) is defined by the -3dB point. So, if you choose 2kHz & 5kHz, changing the filter steepness (or other filter characteristics) doesn’t change what happens at exactly 2kHz & 5kHz… It affects what happens above & below the cutoff frequencies.

There is a free real-time equalizer plugin called TDR-Nova
It has sharp HighPass & LowPass filters . It’s available for MAC , (I’ve only used it on PC).

TDR Nova (free version).gif
Oops I just realized you want band-stop , the above is band-pass :blush:

Thats’s basically how I got this curve. 2000 and 5000 are roughly at the -3dB points and 3000 is down in the trench at about 20dB lower than everything else.


Screen Shot 2019-03-26 at 10.07.17.png
If that’s good enough, I can list how I did it. It was way too complicated compared with a good, single band-stop filter.

I tried variations on Notch Filter, but that didn’t work.

Koz

In the “Draw” mode, it can cut down to -120 dB, though there are a couple of issues with the Equalization effect at the moment.
To use the settings in a chain, I think you have to save the settings as a preset. Also, if two points are at the exact same frequency, only one of the points will be retained in the setting, so you can’t save vertical lines in Draw mode.

The Equalization effect is being reworked for the next Audacity release, so hopefully it will be better behaved in Audacity 2.3.2.

There’s also a “Windowed-sinc filter” available here, which has extremely steep cut-offs: https://forum.audacityteam.org/t/windowed-sinc-filter-steep-cut-off-filter/37426/1
Note that this filter is quite slow. For relatively high frequencies (such as 2 - 5 kHz), a small window size should work well. Larger window sizes get increasingly slow.

Effect > Equalization may be your best bet.


Screen Shot 2019-03-26 at 10.20.12.png
and the spectrum is this.


Screen Shot 2019-03-26 at 10.20.57.png
Audacity Equalization remembers Last Curve Changed in Chains or Macros. So if you want a curve to “stick” forever through multiple uses, change any one control point slightly or add a control point that doesn’t do anything.

Did you think in a million years it was going to be this involved?

Koz