Why do custom Equalization curves need 2 f points of different value

[GWARslave119]

(running Win10 64bit and Audacity 2.3.1)

I used to be able to save a custom curve by clicking point 1, then dragging my mouse to either the left or right to filter out the rest. Past year or 2 though I wasn't able to save those curves, it would save it as a straight line. I just figured out today by looking at the .xml file that if the two f points are of a different value, it will save the curve. Basically, this the old curve:

<curve name="LO">
<point f="80.0" d="-6.0"/>
<point f="80.0" d="-60.0"/>
</curve>

Which is suposed to be a vertical straight line cut off, but gets saved as a horizontal straight line. If I do this though, the curve will save correctly:

<curve name="LO2">
<point f="80.000000000000" d="-6.0"/>
<point f="80.000000000001" d="-60.0"/>
</curve>

Why is that?

edit: Here's a video of what I mean if needed:

https://sendvid.com/tdozxu1l

[kozikowski]

A side note. Even if you do use that program, you're not going to get a sharp shelf filter. You're actually going to get a much more gentle curve such as the green line, even with the filter Length turned all the way up.

Screen Shot 2019-04-12 at 1.45.13.png (26.13 KiB) Viewed 221 times

At 90Hz, it's 36dB down. It's not gone. If you're making critical decisions based on this filter, you should know that.


If the filter Length is not turned up, the green curve is much more gentle. Not only is the attenuation much more graceful (90Hz is only 24dB down), but it's attenuating some of the work at 70Hz and 75Hz.

Screen Shot 2019-04-12 at 1.51.57.png (26.16 KiB) Viewed 221 times

Does this affect your job?

Koz

[steve]

There's a bug listed in the Audacity release notes:

In the Equalization effect if you create a "curve" with a vertical segment, then that vertical segment will not be recalled properly by Audacity when you next use the effect. Also note that you cannot use the "Manage" or the "Save/Manage Curves" - as these will exhibit the same corruption of the curve.

[GWARslave119]

There's a bug listed in the Audacity release notes:

In the Equalization effect if you create a "curve" with a vertical segment, then that vertical segment will not be recalled properly by Audacity when you next use the effect. Also note that you cannot use the "Manage" or the "Save/Manage Curves" - as these will exhibit the same corruption of the curve.

Yeah I remember talking to some people here a while back about it, about how with...oh what version was it, it was before the look of audacity changed. I think 2.1.2 or 2.1.3, where it doesn't have that bug. Didn't know it was listed in the release notes, thanks ;p

[GWARslave119]

A side note. Even if you do use that program, you're not going to get a sharp shelf filter. You're actually going to get a much more gentle curve such as the green line, even with the filter Length turned all the way up.



Screen Shot 2019-04-12 at 1.45.13.png


At 90Hz, it's 36dB down. It's not gone. If you're making critical decisions based on this filter, you should know that.


If the filter Length is not turned up, the green curve is much more gentle. Not only is the attenuation much more graceful (90Hz is only 24dB down), but it's attenuating some of the work at 70Hz and 75Hz.



Screen Shot 2019-04-12 at 1.51.57.png


Does this affect your job?

Koz

Well what I'm doing overall is making songs sound better (better is a preference of course) by...I guess you'd call it re-mixing. Originally a few years back I just wanted to learn how to get rid of clipping properly, and I found a video on Youtube where the guy showed/explained a method to where it "fixes" the clipping correctly, and not just reducing the gain. Back then the vertical curve could be saved. Then I thought, hey lemme learn some audio editing and enhance songs/albums from bands that I like. Up to then I used fruity loops to make drum tracks on some original music, and starting tinkering in everything else FL studio had to offer. Some of the things I do I kinda get, most I don't. But experimenting and trial and error eventually gets u somewhere I guess lol. I can make you a short video if u want on what I'm doing with Audacity and FL studio.

Oh and the filter green curve thingy, I was told, or that guy mentioned, to slide it all the way to the right so the curve gets as close as it can to the initial custom curve I made. I don't really know the correlation between those Hz and dB numbers you mentioned either...and I chose 60dB as the bottom shelf cause I figured the audio is pretty much hiding at that rate. I don't understand that part either, the differnt thresholds and whatnot.

[kozikowski]

what I'm doing overall is making songs sound better

That's one reason we sometimes ask—firmly—that you give us the actual job. That filter and curve won't do that. That's the filter if all you want to hear is trucks rumbling by, thunder and earthquakes. It's probably the exact opposite of the curve you want. The one that removes low pitch distortion, trucks rumbling by and thunder.

There's another thing to note when you try tricks like that. Low Rolloff (there's one built into the Audiobook mastering suite and most Hollywood sound shoots.) is normally done much more gently and not drop like a rock at a certain frequency. Natural sounds aren't just one tone. They're usually a tone and then overtones and harmonics. That's the difference between a good and crappy violin even if they're both playing A above middle C. The drop-like-a-rock filter takes out the tone, but leaves everything else.

So instead of a large, thumpy truck rumbling by, it gives you crisp, tighter, well defined truck rumbling by. Probably not the goal.

I have a field sound mixer with that curve built in, but it's much more gentle and not a vertical line "fall off a cliff" at 80Hz. I do have a picture of it. That's it going out on a job. There's a picture of what the knobs and switches used to say stuck to the bottom if I forget.



By the way, in that first curve you posted? It failed because you told it to do two different things at the exact same frequency or pitch tone. "Reduce the music volume by 6dB and reduce the music volume by 60dB. Call me when you're done." It probably just followed the last instruction it could deal with which is where the straight line came from.

Koz