Hello and thank you for this great product!
Warning: extremely long technical post with only one smiley.
I have never seen a software eq that would be able to follow pitch and "transpose" the bands accordingly. Here's a very simplified example:
you have a bassline playing the A1 note and you make a 12db cut at 82 Hz with a narrow Q and really like the way this sounds. But when the bassline switches to A2 the sound you tweaked so hard is gone. To get it to sound like before you need to make a 12db cut at 165 Hz, but now you already have 2 bands with deep cuts so when the bass switches back to A1 the sound changes again.
Or another scenario: lets say you have a a recording of a live bass and there are some very bad ringing artifacts only when playing certain notes. You could use a sharp and narrow cut to cut them out but now this effects the sound of the non-ringing notes too much. Or you could use wider cuts but that again changes the sound of the notes you don't want changed etc...
Now, if that didn't make any sense please watch this video: www.youtube.com/watch?feature=player_embedded&v=iJNutBk5N78
This is the only eq that I know of that does this (in a way) and I was very excited when I discovered it. And also very surprised that with the gazillion of software eq's that we have on the market today, no one has ever thought to add this feature. Except it is unnecessary complicated and almost never works the way it should - i.e. it uses audio to track the pitch and it is more than most of the time wrong and especially very slow when the notes change. It's especially useless for any kind of fast note plucky type synth basslines.
For myself, this feature would be very useful. Just one scenario: Choose a moogy/plucky type of bass and play a note. Now make a deep boost of 12 db or more an octave or two above the fundamental, optionally make a few additional deep cuts or boosts with a narrow Q - almost creating a comb type filter. You can experiment with the Q and the amount of boost/cut to hear some different results.
Now put a saturation or a distortion plugin after the eq. Especially multiband distortion works great with this. Now the problem here is that the sound changes drastically when you play different notes.
This is where I have an idea that I would like to pimp to the fabfilter team. Instead of using audio to track pitch (like the eq linked above) I would use midi for that.
Audio pitch tracking (realtime at least) never works the way it should (download the demo of that eq to see for yourself) and when you have chords playing or multiple octaves it just turns out to be completely useless, especially for faster note transitions or shorter note durations.
Using midi for this has 2 advantages:
1. no need to spend time programming some algos that may work in an ideal scenario - I imagine it can be done by an experienced programmer in a matter of hours if not minutes.
2. does not add any significant strain on the CPU. Audio pitch tracking certainly does.
3. Works 100% of the time with 100% accuracy! :)
Now you may think this might be useful only for synth, but this can be useful even when working with audio, you simply make a midi track with the sequence the audio is playing. Hell, you could even use something like melodyne for this if you don't feel like doing it manually.
Now, here is how I imagined this to be implemented into Pro-Q:
you insert pro-q on the track you want to eq (standard procedure), now you add a midi track that has the same midi sequence (events) on it as the track with pro-q on it. Now you just route that midi track to pro-q and you're done.
Now, you have to select a root note in pro-q. Let's say you have looped a bar of your bass line which is playing C#2 and you begin eqing it. Let's say you make two bands; one at 69.2 Hz with a 3db boost and another at 500 Hz with a 6db cut. Now if this is the sound that you want for the bass for what ever note progression it is playing you just select C#2 as the root note in pro-q and copy over the midi sequence to another midi track which is routed into pro-q. Let's say the next bar plays E2 -> Since C#2 is 69.2 Hz and you have that midi track routed to pro-q, the plugin shifts the first frequency bands by 9.6 Hz upwards and the second band by 78.8 Hz.
Meaning that our pro-q frequency bands when the bass is playing the E2 note should be at 82.2 Hz and the second one at 594.6 Hz.
I'm a math moron so maybe somebody can check if my math works out. I used this equation for this: www.phy.mtu.edu/~suits/NoteFreqCalcs.html
But anyway, you get the picture.
They say a picture is worth a thousand words, so here's everything routed and working as described and the way I'd imagine Pro-Q could implement this: i.imgur.com/FQ4KR.png
Notice that there are still some open possibilities here. I added a predelay of sorts before the shift to the next note starts to take place and portamento - how fast the shift happens. Portamento is useful if you have some very high boosts in there or a decaying sound so the shift is gradual and doesn't sound instantaneous - unnatural.
This really can't be too difficult to implement and can be highly useful in certain situations and since Fabfilter is the kind of company that doesn't make "standard" plugins I'd figured this might be something you'd give a thought and hopefully we'll see it soon.
God I hope that made some sense...
Anyways, thanks for the great plugins!