And the BIGGEST one of all is 'frequency'. Audio articles actually use the word frequency and use frequency in their explanations. Yamaha seemingly IGNORES frequency whenever possible except in those rare FM-X cases where they just can't.

I've suggested (before) you play a note of a known frequency. I would use FM-X and a single sine wave since this doesn't (ideally) have any harmonics. If you don't know the frequency you can use a free audio scope on your PC or Mac. Both have options and can tell you the frequency.

Slide around the cutoff until you squelch the signal. Here you can know the cutoff frequency and your note played are close. Then you can move to a different frequency and apply the same process to establish your own "map" of the frequency axis on those graphs. You may even be able to mark up a transparent sheet with a sharpie to mark various frequencies to overlay on your graphs if you wanted.

"Should" you have to do this? Maybe not. It'd be better to not have to. That said, the ability to make up for this doesn't offer that huge of a barrier.

My comments are about the transparency of frequencies along the "X" axis. It was a complaint - one that's not nullified. However, dealing with this dimension of the complaint is not difficult.

Sure you cant do a test of one thing but what that does not, and CANNOT tell you is whether that test of one 'note of a known frequency' will apply to EVERY other frequency you choose.

The X axis is frequency. Low frequencies are at the left and high frequencies are at the right. They're not labeled but you can label any point(s) yourself by using the suggestion. It applies to all other notes and frequencies. The more points you plot the more you can be assured about the scale (linear/log) but when they're labeled they're done. It can be good enough to label some point in the middle - some point low - and some point high. You can choose another point to try to answer linear vs. log. After you do this, you're done. You've got the frequencies mapped. Forever - for everything. If you want you can check FM-X and AWM2 and this vs that filter. My assumption is that they're all the same in terms of frequency's representation along the X axis although I haven't mapped to know. What I'm always interested in with cutoff (and sweeps) is where my notes I play in the tune and where they sit. For this I just play those notes and move cutoff in relation to the notes I'm playing to know where to set these. I don't really need to know the frequency of the notes being played. However, if you want to know the missing frequency labeling - it's easily done.

Are all frequencies treated equal for a given LPF filter?

This is a different thing now. You're talking about the Y axis. And of course no - a filter doesn't work like that. An LPF treats notes at frequencies far below the cutoff as "pass through" then starts to squelch frequencies around the cutoff leading to fully squelching frequencies above the cutoff frequency. The exact magnitude of the boost or trim I don't know. The slope we know for LPF24 as 24dB/octave - so that's one thing you can use to help determine "Y" if you really want to know. This isn't as easy as figuring out where along the X frequency is mapped -- the only thing I commented about before.

It simply isn't humanly possible to manually test every possible frequency and every possible combination of cutoff values. And short of testing them all there is no way to know if your test results for one use case apply at all to the next one.

You shouldn't need to map out any more than 4 points to have a fairly high degree of certainty about the entire X axis.

Does a given cutoff value of 83 have the same relation to frequency for all filters? For all frequencies? Does a given change of value from 83 to 127 do the same things for all filters? For all frequencies?

If all you wanted to know is this - then set the cutoff to 83 and fish around for a note that gets cutoff by this. You can usually find 3 adjacent (1/2 step apart each) notes that you can tell are "loud enough" (to hear) for the left most - getting more quiet for the next note - and then silent or nearly silent for the next. Ok - you know how these three piano keys work. Now change your filter with cutoff set the same. You should be able to tell if the range slid around or not. The assumption is that a pixel "1.5 from the lefthand side" is the same frequency for all graphs. That can be tested like this.

Bill!
Agreed on all fronts, and many more.

I've kind of given up expressing the issues with the Yamaha filters since getting to know the Vital synth, as it provides many, many things in the most obvious ways possible, and is free, and I don't think Yamaha is ever going to do anything meaningful about the control of their filters... all of which only further exacerbates the discord of Yamaha keeping even the basic information private, let alone providing visual feedback and access to what's going on with their filters.

eg. Filter cutoffs can be set by frequency or semitones relative to the note played, in Vital. And animated in these units, too. This opens up all sorts of wonderful exacting creativity of modern sound design, sure in the knowledge that your filter moves will do as you want them to do, even though they're moving faster than can be easily visually detected you can be sure they're contributing fifths, octaves or whatever other relationship you'd like, before, after and at points in their animation, in direct correlation with the played notes, without needing to break out instruments to check what's going on.

This then frees up creative energies to be ever more creative in both the sound design and the relationships between different sound designs.

@Bill, @Andrew.... you can stop your jibber-jabber, Uncle Tony is here to help. 😀

I only know of two Analogue Subtractive Synths, of all the Synths made since the late 60's that had a "Frequency Scale" on the Cutoff Knob... The Moog "Model D Minimoog" and the EMS VCS3 "Synthi". And in each case, these were a visual guide only, not a metric, and probably no player ever looked at them anyway.

TUTORIAL #2 - Cutoff vs Harmonics
Remember, Subtractive Synths had only a few Waveforms to choose from, and in each case, the lowest (fundamental) Harmonic was not only the loudest, but also the "Pitch" of the Note being played.

Using the "440Hz A4" again as an example. If the A4 key is held down, and the LPF Cutoff is reduced, then when the reduction in Cutoff results in Silence... then you know that it is at least lower than 440Hz because it is "Cutting Off" 440Hz... hence the silence.

But, there's a more accurate method to set the Cutoff directly on 440Hz.

Sorry guys, but yes, you must use your ears and it is NOT a cop-out. Every Synth player that ever existed since the 60's to present day uses this method. It is not a trick.

Turn UP the Resonance on the Filter.

On the MODX, I recommend you turn the Master Volume down AND turn the Filter Gain down to about 180-190.

Remember Resonance BOOSTS the frequency at the Cutoff point.. you don't want to damage your hearing, or speakers. If that cutoff frequency is at a Harmonic it will be louder than the Frequencies immediately either side of it (these inbetween, lower volume frequencies are called side-bands... more on that later).

The "Fundamental" is the First Harmonic and it is also (by far) the loudest.

Do this as an Exercise:-

INIT
Part1, Element 1 = "OB Saw" (a Saw Wave).
Set FEG Depth = 0
Set Filter Type = LPF24A
Set Gain = 180-200... watch your volume, lower if it starts to distort/clip.
Set Resonance ~ 80 or higher for more obvious effect.
Set Cutoff = 255
Set Cutoff/Key = 0% (important, more on this later)

Now play and hold "A" at 110Hz, I believe on MODX, this is Labelled "A1".

It is a "Bass Note".

While holding the Piano Key, slowly reduce the Cutoff from 255 with the Encoder Wheel.

As the Cutoff Value reduces (at first it will seem to do nothing) the Timbre will get darker... but Harmonic Notes will start to "Pop Out" louder, and it sounds like a descending Arpeggio (which it is... of an A13 chord).

When you hear the lowest and loudest Harmonic... and believe me you'll hear it, the Cutoff (Resonant Peak) is sitting right over 110Hz... the Fundamental (Sine Wave) of A1.

Lower the Cutoff below this, and it will just reduce in volume (no more harmonics) until you get Silence... A1 is, literally, Cut Off... it is History.

That's why you don't need X-Axis Scales and Slide Rulers.

You tune the Filter like you would tune a Guitar String to its adjacent Guitar String... with your ears.

One last important note in this Episode.

With Cutoff/Key = 0%, the Filter is in "Absolute Mode" ... there is no Cutoff "Key Tracking". The Cutoff Frequency is NOT being influenced by the piano key you play. The Cutoff Value you set is static/fixed, regardless of the notes you are playing (more on this in the next post).

In this case (no Key Tracking), Cutoff = 255 is fully Open. The Frequency Value is immaterial, it is way above what we, or even Bats can hear.

Cutoff = 0 is Fully Closed. It may actually be a Frequency of a few Hertz, but again immaterial, since it is below our hearing range. Maybe Blue Whales could hear it though.

Now with Cutoff/Key = 100%, you are making the Cutoff Frequency fully "Key Tracked". If you set the Cutoff Value (Frequency) to a Point where it is clearly impacting the the Note you play, then that same impact will be experienced by ANY note you play.

Recall I mentioned the Term "VCF". In classic Synths, each Incremental piano key, produced an Incremental, specific voltage. This voltage was used for example to set the Pitch of the Voltage Controlled Oscillator... A2, F#3, C4 etc.

The same voltage could be used to increase the Cutoff Frequency above or below that set by the Cutoff Value. It added an "Offset", aka a "Voltage Bias" that followed the Key being played. This is what is known as "Key Tracking the Filter".

So, with 100% Key Tracking, the Cutoff Frequency you set on one chosen Note, is exactly the same "musical interval" above any other note you play. Audibly this means you get the same Timbre on every key. By contrast, 0% Key-tracking results in higher notes getting duller and quieter to the point of silence.

So already you can see that a Frequency Scale on the Cutoff Knob, at this point, is meaningless. The actual Cutoff Frequency will be something different... it is being Modulated by the Piano Key or Keys you are playing.

@Bill, @Andrew, please... just do the exercise, and then we can continue without the confusion. 😉

In a general sense, the filter cutoff does not have a direct relationship with the fundamental. It has a relationship with a specific fundamental - but you seemed to be speaking more generically. The fundamental when you strike any specific key is a specific frequency (particularly when using FM-X to synthesize a tone with no harmonics). Different keys will have different frequencies according to the microtonal scale setup. Since you can play any note across the keyboard, I don't really see this as "a fundamental" (singular). For any single note, on a spectrum analyzer there will be one huge spike somewhere along the right-left area in frequency. That's one frequency and one X-axis point.

Cutoff doesn't track your keyboard. It stays fixed as you play higher and lower notes. There are some parameters to scale cutoff with key played - but this discussion assumes you're not doing this as this would add yet another needless moving target obscuring understanding.

The fact that cutoff doesn't move means you move the frequency to it. You play notes up and down and will understand where a cutoff of "0" or "85" or anything you choose relates to notes played. The scale would not be difficult to determine and without many swings at the plate - you'll have the whole thing.

With all due respect Jason, I must strongly disagree with your last post.

There are two "main" scenarios.... Filter not Key-Tracked and Filter 100% Key-Tracked. There are also 100 minor points in between the two.

With no Key Tracking, the Cutoff is fixed at whatever Value you set it to.

An easy demonstration of this (With a Saw Wave Element) is to set Cutoff very low, and then play a very high note on the keyboard, and hear Silence.

You have pre-empted my path a little, but the method of setting (choosing) Cutoff with 100% key-tracking is a different approach.

Again using a Saw Wave example, you set the Timbre (a Filtered, duller Saw Wave for example) on any key. That same Timbre will then be reproduced on any Key you play. My recent "Everything In its Right Place" would be a reasonable example of this, if you set Cutoff/Key = 100%, rather than the "80%" I specified.

Using Filters after FM-X Parts changes the ball game. FM can, and will, produce an uneven distribution of Harmonics (learned from Manny's Tutorials). In FM-X, the "Fundamental", I.e. the note being played, is not necessarily the loudest harmonic (or even the lowest). This is why FM can sound out-of-tune or dissonant.

Filter Key-Tracking is a "Topic" I was going to cover here (and still will) that took me a long time to get my head around (the Hydrasynth helped greatly because it is pure VA Subtractive Synth at its heart, with very detailed Filter and Oscillator models).

Last point on this for now, Key Tracking is basically an "Offset" (a term we are all familiar with) which can be positive or negative relative to the Cutoff Value. The Keytrack "Centre Key" is C3 (in Yamaha land at least), and cannot be changed.

If you set your "Filtered Saw Wave Timbre" with the Cutoff Value while playing C3, then notes lower than C3 will be subject to a Lower Cutoff than that set by you. Equally, notes higher than C3 will be subject to a higher Cutoff Value.

But importantly, the "distance' between the Fundamental (note played) and the Modulated (Key Tracked) Cutoff Value will remain the same.

I want to avoid Frequency "Numbers", but if you tuned the LPF to Cutoff at "C4" when you were playing C3....

If you played E2, the Cutoff would be E3.

If you played F#4, the Cutoff would be F#5....

Try it, honestly, it works. I just spent the last month on changeover to the MODX making sure it does.

Starting with the simplest case, if I initialize using "Init Normal (FM-X)" and set the cutoff key scaling to 0 then all filters will not have key tracking. This is the easiest case to consider since it removes having to discover how to deal with the cutoff's key scale for that parameter.

Starting here, we will see that the A above middle C has an approximate value of 127. Every octave is 25 cutoff values. An A the octave below will have a cutoff value 102 (127-25) and an A an octave above will be a cutoff value of 152 (127+25). Each octave is a linear relationship with the cutoff value. All of this is easy to determine and takes maybe 15 minutes. The cutoff value is near the top of of the slope. You can prove this by increasing resonance - which peaks at the top of the filter graph's "roll off" and you'll hear the strongest resonance here at your cutoff value (the note I mapped to a cutoff of 127 as "A").

I didn't say you couldn't do key tracking - only that if you're learning the ropes it's one dimension that would best stay fixed (don't do key tracking) in order to learn what a filter does. Learn the non-tracked behavior first.

How to map frequency to these graphs is dead simple.

The cutoff values for LPF and BEF tracked frequency in the same manner. One can extrapolate that all filter types are similar.

Maybe.... what I'm saying (in response to immediate posts after my OP) is that having a Frequency Scale on the "Pictorials" serves no purpose.

Like Bill and Andrew, I too have become a bit sick of "Use Your Ears" responses to "What does parameter X do?"

But...

In the case of Filters, using your ears is absolutely the "normal" way, but really, it is the only way. They're not intended to be scientific, they are intended to be musical.... move them until you "hear" the sound you want.

Typical home "HiFi" Treble, Middle and Bass controls are a semblance of (typically) 6dB/Octave (1 Pole) Filters, but you never see "Frequency Hz" scales on those, with never a complaint.

These Filters on the Montage/MODX are there for "Subtractive Synthesis"... it's their "Raison d'etre".

Available on FM-X is more a case of "Wouldn't it be fun if...?"

Using these filters with Subtractive Synth Oscillators (Sine, Triangle, TriSaw, Saw, Square, Pulse[%]) is absolutely essential to understanding why they exist in Subtractive Synthesis... and why they are there in the OS.

A little bit of vitriol here from watching MODX YTube demos... "And here we have a nice Jazz Piano, and look we have a nice Low Pass and High Pass Filter which I can use to make my Jazz Piano sit nicely in the Band Mix when playing Live. And I can also bring those controls up to the SuperKnob.... Yada yada yada".

That is absolutely NOT why there are LPFs, HPFs, BPFs and BRFs on the Montage/MODX.

No wonder the MODX crowd don't get it... it's because they're presented for the wrong purpose almost 100% of the time in Official demos.

Leave FM-X out of it for now. Leave specific Frequency values out of it for now.

Instead, seriously, use your ears, and listen to what a moving Filter does to your sound.

It is key.

Absolute Frequency Values, X and Y Axis Scales, benchmarking.... it is all just obfuscation. It is entirely irrelevant.

It's about music. Music is about listening.

All fair - there are multiple topics here and I was laser focused on the complaint that the graphs don't have frequency labeled in absolute terms. I agree that you don't need to know - that it's more simple to just play a note and move around cutoff until you "find" where the sound starts to get filtered. It works better to use your ears than care about A440 being 127. However, if you're absolutely bent on this because you have some other product's documentation that does have frequencies shown (or some youtube video that describes things in frequencies and cannot otherwise understand the content without a 1:1 experience on MODX/Montage) -- then it's not too difficult to derive these yourself. I too do not see the point in doing this - but still there's an easy way.

The only topic here was a general layman's tutorial in How/What/Why to use Filters on the MODX (& Montage), for the wider MODX User Audience. There were no complaints in my OP, and still aren't from my perspective.

It was entirely predictable that Bill and Andrew would pounce on this thread (or any thread) before the OP Ink had dried. The other topics you refer to were carpet bombed into the thread thereafter. Like I said... obfuscation.

I'll continue regardless, other MODX users will find it beneficial, that's my purpose. I find myself with enough spare time to accomplish that.

I am writing from my perspective and memory of the teething pains I experienced when I was new to the MODX and Synths in general.... the MODX was my first Keyboard (and Synth) ever.

This site helped me learn. It's a case of repaying favours... Pass it forward.

TUTORIAL #3 - Keyboard Tracking

This can be a tricky subject to get your head around, but it is essential to using Filters effectively.

To be clear, Keyboard Tracking is a form of Filter Cutoff Modulation, using the Pitch of the Piano Key played to alter the Cutoff Value.

On the MODX, Keyboard Tracking is set by the parameter:-

"Cutoff/Key" On the Element - Filter - Type Page.

Cutoff/Key = 0% = No Keyboard Tracking (No Modulation)
Cutoff/Key = 100% = Full (1 to 1) Keyboard Tracking.

We will look at the in-between (1% to 99%) values later.

Full Keyboard Tracking
In the case of Full Tracking, the current Cutoff Frequency will be incremented or decremented by the equivalent of 1 Semitone of Frequency for every Piano Key above or below the Centre Key (on MODX this is C3 = 256Hz*)

[* In classical Music Theory, 256Hz is known as "Middle C" or "C4". MODX labels this as C3 on the Keyboard, I don't know why and it does not matter. We will use MODX Key Labels].

So....

With Cutoff/Key = 100%
Set Cutoff = 160 (entirely arbitary)
If you play C3, the Current Cutoff is not Modulated by C3 because C3 is the Tracking Centre Key.

If you play G4, the Current Cutoff Frequency (Value = 160) is incremented by the equivalent of 19 Semitones = +1 Octave + Perfect 5th, because G4 is 19 Semitones above C3. It does NOT mean the Cutoff Frequency = G4.

If you play F#1, the current Cutoff Frequency will be decremented by the equivalent of 18 Semitones = -1 Octave - Tritone, because F#1 is 18 Semitones blow C3.

There is no "fixed" Frequency amount per Semitone, this is because Musical Frequency Intervals are Logarithmic... not linear. This is why I say the "Equivalent" of 1 Semitone. We do not need to know exact values in Hertz, only that it parallels the Pitches of the Piano Keyboard.

What does this mean?

It means with Full Key Tracking, the Filter Cutoff Frequency will "follow" the Note's you play on the Keyboard. In an LPF, this means the Filter will open as you play higher and close as you play lower. In an HPF, the Filter will close as you play higher, and open as you play lower.

In any case, the Filter Cutoff Frequency cannot go above its maximum (value 255, fully open in LPF), or below its minimum (value 0, fully closed in LPF).

Why do we need Full Keyboard Tracking?
Take an example, with NO Keyboard Tracking.

Your Oscillator is set to a Saw Wave, and the piece you are playing centres around the C2 to C3 area of the Keyboard.

A Saw Wave is very bright, buzzy and harsh... not pleasant. So, you set the LPF Cutoff so that the Saw Wave is "Filtered Down" removing the harsh high harmonics. Now when you play C2 to C3 you get a pleasant, mid-ranged tone, similar to the Timbre of a Cello.

You can imply the LPF Cutoff Frequency must be set around or just above C3... just by using your ears, and without needing to know the exact Hertz value.

The problem arises, Part of the musical piece requires a short solo lead played in C5 to C6 Octave. Except when you play C5 to C6, the notes are quieter and sound like Sine waves (not high strings on a Cello). This is because the Note's are above the LPF Cutoff Frequency, and are therefore being Attenuated and Cutoff.

It is preferable to have the Filter "Open Up" only when we play these High Notes, so they can be heard AND maintain the "Cello" Timbre. This is why we have Filter Cutoff Keyboard Tracking.

Now, 100% Keyboard Tracking would work. But... we may find these High Note's are TOO Bright to sound like a Cello. We would prefer if they were less bright, but still thick, not sine waves.

In this case, we would turn down Keyboard Tracking (from 100%), using our ears while playing the high notes, until the Brightness was dampened sufficiently... we will end up with a Tracking Value of less than 100%. Having done this, and fine tuned with our ears, we may find that the Keyboard Tracking is now at 71%. It is only partially tracked, but it suits our purposes, because it sounds correct.

This is where those in-between Keyboard Tracking values become useful, or arguably necessary.

Incidentally, the MODX allows Keyboard Tracking above 100% and below 0%. These provide more flexibility for "experimental" scenarios. Typically you would not find these options on a traditional Analogue Subtractive Synth.

I will follow up with some Keyboard Tracking Exercises that will help visualise Keyboard Tracking in play.

TUTORIAL #4 - Keyboard Tracking Exercises

We're going to stick with AWM2 to keep things simple and relevant to Subtractive Synthesis. I may do an FM-X comparison at the end.

Notice that on MODX AWM2 INIT Patches, the Filter Cutoff is set to "160", Cutoff/Key = 31% and FEG Depth = 40. Just as a point of Note, the Filter IS active with these settings, and is presumably set like this to dampen the very high keys for a more pleasant hearing experience. Going forward, for the purposes of demonstration, it is best to set Cutoff = 255, FEG Depth = 0 and Cutoff/Key = 0% unless otherwise stated. Maybe create your own "Filter INIT" Patch and Store for use going forward.

Exercise 1 - Make a Filter INIT Patch

Select AWM2 INIT
EDIT Part 1, Element 1
Change Waveform to "OB Saw"
Set Filter Type = LPF24A
Set Cutoff/Key = 0%
Set Filter Gain = 180
Set Filter FEG Depth = 0
Edit Part 1 - Common, Rev Send = 0
Store the Patch "Filter INIT"

Exercise 2 - Keyboard Tracking Sine Waves

Open "Filter INIT"
Change Element 1 = Sine

a) Play all notes on the Keyboard. You will hear a Sine Wave on every Key. (Filter is Fully Open, Not Tracked).

b) Set Resonance = 70. While playing and holding C3, use the Encoder Wheel to reduce Cutoff Value down from 255. You will hear to C3 Tone get very loud with Cutoff = 105-106. Cutoff = 104 and Cutoff = 107 are quieter. With Cutoff = 105 or 106, you have now tuned the Filter Cutoff to 256Hz (like tuning a Radio).

Play C2, and C3 separately - They can be heard as "Normal" Volume Sine waves because they are below the Cutoff Frequency and are not resonating.

Play C4 and C5 separately. C4 is barely Audible, it is 1 Octave above C3 and is being Attenuated by -24dB. C5 is inaudible, it is 2 Octaves above C3 and is being Attenuated by -48dB, it is "Cut Off".

c) Set Cutoff/Key = 100%
Now play every key individually. You will hear a Loud Sine Wave on every Key. Every Key is playing a Resonant Sine Wave. That is because each Piano key is Modulating the Filter Cutoff, so the Resonant Cutoff Frequency is moving to Coincide with each Piano Key.

The Filter is now Fully Keyboard Tracked.

d) Set Cutoff/Key = 66%
You will find the further you play away from C3 (above and below) the quieter the Sine Wave, but not as severely as with Cutoff/Key = 0%. You have introduced a form of Keyboard "Scaling" using the Filter Tracking.

Exercise 3 - Keyboard Tracking with Saw Waves

Repeat the above using Saw Wave (OB Saw) instead of Sine Wave. Cut to the chase, change Cutoff above 105-106 (to allow more harmonics through) to 153. It should sound a bit like a Vox Continental Organ.

With the Saw Wave notice the Change in Timbre, as well as the Changes in Volume with different Key Tracking values up to 100%.

Saw Waves have clear Harmonics. Instead of tuning the Filter Cutoff to the Fundamental (as we did with the Sine Wave), instead, tune the Filter Cutoff to the 3rd Harmonic... that is the 3rd Resonant Peak you hear above the C3 Fundamental (counting the Fundamental as the first Resonant Peak).

Now when you turn KeyTrack to 100%, the Filter Cutoff will "Track" the 3rd Harmonic of each Note you play (The Cutoff Frequency will be higher than each Fundamental Key Pitch you play.).

This demonstrates how Filter Tracking can maintain Timbre across the Keyboard.

Reminder: Timbre is the Composition of Harmonics, or Harmonic Profile, or Harmonic Spectrum of the note being played. With Key Tracking at 100% the Harmonic Profile is maintained for any Note you play.

TUTORIAL #5 - Keyboard Tracking Summary

There are some anecdotal considerations when setting the amount of Keyboard Tracking.

The first is, 100% Keyboard Tracking is not necessarily the most desirable, although it is the most "accurate" and predictable.

In truth, the "right" value needs to be assessed subjectively, and this can mean trial and error. Play the piece through several times with different values of Keyboard Tracking (and usually compounded with different "starting" Cutoff values) until you "Zero In" to what sounds best or "right" to your ears.

It's best to do this without any other Modulation in play (Envelopes, LFOs, Velocity etc), to get a sense of overall Timbre.

This is why I suggested that Keyboard Tracking is the most difficult to comprehend (to "get your head around") and why I dealt with this form of Cutoff Modulation first.

In an ideal world, you could set your own "Tracking Centre Key" as an Anchor that doesn't change. Typically, on any Synth, the Filter Tracking Centre Key is fixed. On the MODX it is C3 (256Hz, C4 to the rest of the World). On my Hydrasynth it is C2 (equivalent C1 on the MODX).

If the piece you are playing coincidentally happens to be around the Centre Key, it helps. The more likely reality is it will be 2 or 3 Octaves beyond, making things quite tricky.

I use/follow a method for setting Key Tracking.

I look at the Lowest and Highest notes in the Musical Piece I am playing and use them as brackets (or limits). I just play these two (lowest & highest) notes, then compare using my ears.

I typically run through the following Key Track values to develop an estimate of where the right KeyTrack value should be:-

0% = No Key Tracking
33% = 1/3
66% = 2/3
75% = 3/4
90% = 9/10
100 = 1/1 Full Key Tracking
It gives me a consistent frame of reference, but you can develop your own.

Rules of Thumb... (Saw Wave with Arbitary Cutoff Value of 150... choose any, experiment and listen)...

With 0% Key Tracking... higher Notes are darker/duller. Lower Notes are brighter/fizzier/buzzier.

With 50% Keytrack, Higher notes are a bit brighter, but still not as bright as lower notes.

With 100% Keytrack, High notes are equally as bright as lower Notes.

If you find the Bass notes in the piece have too many Harmonics and messing up (interfering with) the Higher notes... Lower the Cutoff and Increase the Keytracking.

If you find the Higher Notes Harmonics are "Fizzy" and the Bass is a bit Flat/Boomy in comparison.... Raise the Cutoff and Decrease the Keytracking.

Tutorial #6 - Sweeping the Filter Cutoff

This is a precursor to using Envelopes. It's important to understand how manually sweeping the Cutoff affects the sound, so you are better prepared for designing your Envelopes.

By now, you will have noticed that slowly "Sweeping" the Cutoff on a "C3 Saw" from 255 down to 0 does "nothing" in the Higher Range of Values (C3 still sounds like a Saw), and does "nothing" in the Lower Range of Values (C3 remains silent).

Open up your "Filter INIT" Patch and try it.

Play and Hold C3.

Using the Encoder Wheel, gradually reduce the Cutoff Value from 255 down to 0.

You will find:-

255 down to 220 does nothing. Those of you with keen ears may notice a little high end "Air" disappear from the sound, but it's nothing dramatic.

219 down to 181 darkens the Timbre. The Saw Wave is changing "Tone", but it is still recognisable as a Saw Wave.

180 down to 118... you can start to hear some "warbling" going on. It sounds like maybe the Volume is Modulating (Tremolo), but there's also some noticeable "up and down" shifts in Timbre.

117 down to 100... the Timbre is now recognisable as a Sine Wave. Bluntly... it does not sound like a "Saw".

100 down to 74... is a gradual decrease in volume of the Sine Wave.

74 down to 0.... Silence, for all practical purposes.

Repeat this exercise again, with Resonance set at 32, then 64, then 80... for your own observations. The "Tremolo" effect is more obvious... louder Harmonics interspersed with quieter Sidebands... and it is more noticeable, the nearer the Cutoff Frequency is to the Fundamental.

Repeat all the above but use a 12dB/Octave LPF (Filter Type = LPF12 + HPF12... just leave all HPF settings at 0). You will have less distinct patterns, but in return you get a lot more "colour and vibrancy" with the Sweep (maybe a poor choice of words but your ears can provide your own description).

The main item I hope you observe is that the LPF Cutoff range has "Dead" or "Uninteresting" zones, where altering the Cutoff Value doesn't do very much.

To my ears, these "Dead Ranges" are 0 to 74, and 181 to 255.

But... if we sweep the Filter between 75 and 180... "Interesting Things" happen.

This is because the in range of 0-74 the Cutoff Frequency is way below the Fundamental of C3, and in the range of 181-255, the Cutoff Frequency is above the Harmonic Bandwidth of a C3 Saw Wave (at least, the affect is negligible).

As wise people, we don't want to waste any energy changing the Cutoff Value in these "Dead Ranges".

Instead, we want to limit any "movement" of Cutoff to the "Active Range" where interesting things happen.

So for a C3 Saw, the "Active Range" is 75 - 180.

But, different "interesting" things happen within that range, depending on "where" in that Range our Cutoff is AND the current level of Resonance.

We could just sweep that whole range... or we could just pick out a smaller "Sub-Range", or "Sweet Spot" to sweep through.

This is where it becomes obvious that your Ears and your Musical Subjectivity are all that is needed. You do not need to know the "Frequency Values"... all you need to know is "Which bits do you like?" and "Which bits don't you like?".

It's like ordering a Hawaiin Pizza, eating all the Ham, but leaving the Pineapple chunks.

I will hark back to what I said in Tutorial#1... to hear and know what a Filter is doing, you have to hear it "Moving"... by "Sweeping" it's Cutoff.

For arguments sake... let's say you like the "Sweep" between 118 and 162. That's on a C3 Saw.

Now you play a C5 Saw, and Sweeping 118-162 doesn't sound as good. Or you play a C1... same again.

In truth, for C5 and C1... you'd need to Sweep a different Range to get the same effect...

UNLESS....

You set Filter Key Tracking to 100% (or something close).

Equally.... you might like the fact that "a different effect" happens on C1 and C5.... it adds colour, because the sound is different the higher up or further down the Keyboard you play.

So you would leave Key Tracking on 0%.

Or What the Heck!! Set it to -33% or +133%.

You are The Boss!!

But let your ears take in the sounds you have discovered with a Manual Sweep and make a mental note.... because Next... you are going to make the Filter Envelope do the Sweeping for you.