Remove Q setting from high-pass / low-pass filters

As illustrated in this post the “Q” setting in the high-pass and low-pass filters is a source of confusion.

For the vast majority of user cases, the Q setting should remain at the default (0.7071) as this produces the most accurate 12dB per octave roll-off without accentuating frequencies at the cut-off point.

Additional points:

The only argument that I can think of for retaining this feature is so that high Q settings can be used as a “special effect”. I’m sure that a few users would find this feature useful, but the plug-in defeats this use by limiting Q to a maximum of 20. To use the Q control as a special effect one would probably want a much higher setting (100 or more).

Also, this effect allows invalid filter frequencies that can corrupt the audio data (for example using a 12kHz filter frequency on 16kHz sample rate audio. (In some older versions of Audacity this will corrupt the entire project.)

Also, should it be:

  • “rolloff”, “roll off” or “roll-off”?
  • “12dB” or “12 dB”?
  • [‘ringing’], (‘ringing’) or (ringing)?


  1. That the Q setting is removed from the standard high-pass and low-pass filters (as distributed with Audacity). This will simplify the effect for users with no impact on its functionality for general use high-pass / low-pass filtering and will ensure that for such purposes the user will be using the optimum Q value.

  2. That error checking is built in to prevent frequencies above the Nyquist frequency from being applied.

  3. That round brackets are used in the ;info text.

Optional points:

  1. That a new high-pass / low-pass filter plug-in is released as an optional download for “special effect” purposes that allows unlimited Q values.

  2. That the high-pass and low-pass filters are combined into one effect.

  3. That the high-pass and low-pass filters are combined into one effect with the option of band-stop and band-pass filtering.

Usage of the verb would usually be “roll off” but as a noun I tend to think “rolloff” is more common. Wikipedia has “roll-off” as the noun and verb. 78 EQ Generator has “rolloff”. I would have a weak preference to let sleeping dogs lie.

NumberdB is I believe correct as now.

+1 on your proposals 2) and 3), though if we do 3) I think we should use round brackets for control units as well. Otherwise these two plug-ins have “(q)” in ;info text and “[q]” in the interface.

-1 to 4) unless there is considerable demand.

1), 5) and 6) are inter-related really depending how much extra complexity is wanted and what the demand for the features is. I have long thought we should have a band pass filter but tend to think separate high pass and low pass filters are an aid to understanding. Would a band pass filter that combined High Pass and Low Pass be too complex? It might be interesting to see a mock-up.

Having a q option for -12 dB rolloff is fairly marginal - if we have it at all, would high q values still only affect -12 dB? One solution might be to limit the q slider to a narrow range around 0.7 but allow text entry of any value?

Wouldn’t band stop be better in a “Band Stop” effect that included Notch Filter, at least logically?


I have a marginal preferences for “roll-off”. Is there any precedent elsewhere in Audacity?

I see that’s the case in the manual though there is inconsistency in other plug-ins. “Leveller”, “Equalization” and “Truncate Silence” do not use a space.
There appears to be one consistent exception which is when labelling a graph (for example the “Compressor” effect).

Good point, though if the Q control is removed then it will not be either the ;info text or the interface.
I’m gradually coming round to your general point about using round brackets rather than square brackets in the interface, though the use of square brackets is ubiquitous in existing Nyquist plug-ins.

  1. A “high Q” high/low pass filter could probably be included in a “resonant filter” effect (useful in sound synthesis). I’m not suggesting this to be bundled with Audacity, just available to download from the wiki.

I’m not sure - I’ll give it a go.
I think combining high-pass and low-pass would be simple enough, especially without the Q setting (and it should be upper case “Q”).

Functionally they are similar, but they take different parameters, which I think would make the GUI confusing.
For a notch filter there are 2 parameters: Frequency and Q
For a band-stop filter there are three parameters which can be either: Centre frequency, Width and Roll-off, or Low frequency, High frequency and Roll-off.

Band-stop and band-pass could certainly be combined.

Here’s a combined High/Low pass filter. It will appear in the Effect menu as “HL-Filter…
hl-filter.ny (1.62 KB)
And here’s a combined high-pass/low-pass/band-pass/band-stop filter. It will appear in the Effect menu as “Filter…
hlbfilter.ny (2.81 KB)

Here’s the full High/Low/Band filter without all the extra text in the ;info line:
hlbfilter.ny (2.25 KB)
(If this was included with Audacity, then the extra ;info text would probably not be necessary as it would be in the manual for anyone that could not work it out themselves).

Not in Audacity itself. All the references in the Manual say “rolloff” but that is the author’s preference.

I can understand/support “no space” in a graph. My beef with no space otherwise (especially in a line of text) is that it’s confusing and simply hard to read. Note that the dynamic text for the Compressor sliders has space and I think it would look odd without.

Given that changing strings now could break translations for 2.0 it’s not the right time to change them for cosmetic reasons, even though I personally dislike any sort of inconsistency like this.

As you know I think there are too many separately downloadable plug-ins that are the same as the Audacity equivalent (or as other separately downloadable plug-ins) except for one or two controls. If you can dream up a “resonant filter” that is sufficiently different, I’m fine with it.

It’s probably harder to make a band stop/notch or pass/stop/notch intuitive as a Nyquist effect than as a built-in effect. I think it could possibly work as a Nyquist effect by interpreting what one or two frequency values “mean” according to choice of notch/stop/pass?

To look at, “hlbfilter” doesn’t look cluttered at all as long as there is no ;info text. Without the text, I would still be a bit worried about the “hey you’re doing Microsoft again making formerly simple things complex with too many options” type of comment. People who understand band pass and band stop could probably cope with notch included in it.

I have not tested either of your two plug-ins.

Combining High Pass and Low Pass in one effect and “Band Pass/Stop” in another wouldn’t add to the total number of effects even if “Notch” was kept separate. But if there are lots of people who only do whichever of High or Low Pass isn’t default in a combined effect, they could get pretty irritated.

Anyone else?



That appears to be a recent change. Up until March 20th this page used the hyphenated version
I’ve tried a couple of spell checkers and they highlight “rolloff” as an incorrect (US or UK) spelling. I suggest we go with Wikipedia on this one and hyphenate “roll-off”. Google searches for “rolloff” also suggest “roll off”, but accepts “roll-off” (Google search does not use hyphens).
I also notice that Wikipedia uses “cutoff frequency” rather than “cut-off frequency” (don’t you just love the inconsistencies in the English language :smiley:)

For “Truncate Silence” and “Leveler” it is only in the multi-choice drop-downs. Do these get translated?

I agree, though at present we do not offer a resonant filter so it could be a useful addition.

Assuming that we do want a band-pass/band-stop filter, we have the option to have high-pass/low-pass/band-pass/band-stop all as separate effects, all combined into one effect, or any combination between.

I rather like combining all of them into one effect as then, whichever effect I want to use, I only have to look for one “Filter” effect in the Effect menu, rather than skipping up and down in the alphabetic ordering looking for the right one.

Combining high/low-pass and band-pass/stop as two effects is a good compromise as it keeps things extremely simple while avoiding the (unnecessary) clutter of 4 separate effects.

Whichever solution we go for, I’d like to get rid of the “q” control, which in my opinion is an unnecessary complication with little practical value.

OK it was author’s choice tempered by the proofreader (me). However I went for “rolloff” because I thought in audio circles (as opposed to everyday parlance) that was more common:

Plus most of the record playback EQ charts I have ever seen say “rolloff”.

I certainly found examples of “roll-off” and “roll off” too, though not as many as “rolloff”. The lp2cd site has “cut-off” in spite off “rolloff” so I went with that pair - it tends to accord with the pro usage I’ve come across.

If we want to make a ruling about hyphenating these types of words (so “roll-off”, “cut-off” as well as “plug-in”) I don’t care as long as it’s done consistently.


I think four-in-one is a step too far, and eventually we will have some sort of grouping feature (well, we have it now if you turn on EFFECT_CATEGORIES in the code).

Would it be worth having a Forum poll to see if there is a) resistance to combining High Pass and Low Pass and b) if combined, is High or Low the most useful default?

I’ve no objection, though I’ve suggested a possibly less confusing way of retaining it by forcing text input if you want an “exotic” value.


“rolloff” appears to be more common in American documentation (when used as a noun), so as the Audacity documentation is in US English I agree we should go with that.
“cut-off” is virtually always hyphenated, and “plug-in” is already specified for Audacity documentation.

For “Truncate Silence” and “Leveler” it is only in the multi-choice drop-downs.

I think I can fix this.

I’ve never had much response to polls on the forum, but it does give people the opportunity to have their say so I’ll set one up.

Poll created here:

@Steve: I moved this from the “Adding Features to Audacity” section of the foum to here on the Nyquist section as per your PM. I ill leave it to you as to what you want or need to transfer to the Wiki as a proposal.


Apropos of the recent discussion threads on the Manual mailing list (re cut-off v. cutoff)- I note that both of these effects still use the unhyphenated “cutoff” in their dialogs.


The issue (now fixed) with Truncate Silence and Leveler was no space between value and dB so that part of the quote isn’t really relevant.