I have to remind myself of the importance of this project. It's not so much recreating DX7 sounds in the Thor synthesizer. It's more about what kinds of sounds we can spin off from them.
It's also about learning the synthesizer and coming up with ways of solving problems. We've already established that there can be no perfect replication of the DX7 architecture in Thor. We have, though, also established that by mimicking DX7 architecture (feedback loops, long chains or stacks of modulators and carriers) we can get results that approach the DX7 patch. I think that certain kinds of sounds are enhanced by these differences.
But sometimes these differences can make life really complicated for us. This week, we'll examine Gong 1.
Gong 2 is actually more difficult. But in looking at Gong 1, we can gather some clues that will hopefully make the variation a little easier to understand.
In making a synthesized FM gong sound, someone spent some good time working out how to emulate some of the nuances of a real gong. So imagine the sound of a lightly-struck gong. The initial sound is a pretty but deep, slightly ominous bell sound. Along those same lines, consider that the gong will have similar properties as bells and cymbals. This means a strong fundamental with unstable harmonics, maybe even some pitch instability as the gong settles into its core sound. There might also be a slow, gentle rise in those upper partials.
Translated into FM terms, this means at least two distinctively different envelopes--immediate attack and a slow attack, long decay times on both. We need a solid fundamental tone but with a first partial that is relatively close by. We'll have to be creative in picking out inharmonic partials and ratios and devise interesting ways of maintaining sidebands.
This is very much unlike any patch I've created up to this point!
Looking at the FM Matrix in FM8, we have a single carrier (at the bottom) modulated by 2 mod/carrier pairs and a single modulator. I don't normally consider this to be a problem. Big deal... Start at the top and work our way down, right?
Here's the problem with the usual routine: Look at ops A and B, C and D as mod/carrier pairs and consider their ratios. We have 1.2:1.4 and 3:0.745. OK, no problem. We'll simply use the chorus effect since this is obviously a product of detuning. But what about the last mod/carrier pair, the carrier being the only real carrier in this algorithm? Here the ratio is 0.8:0.5. This tells me that if what we're doing is a product of detuning, it's going to be a wild effect.
While I'll always champion the art of listening, I think what we need here is some basic mathematics to help us rebuild this FM gong timbre.
I'm not very good at math, so let's go ahead and get that straight right now! I'm not worried about getting everything exactly right: My satisfaction is in whether or not I like the results. We have to start with the core sound, and since the other oscillators will be routed to this one, let's start with oscillator 3.
Here's what I did: To get something like a ratio of decimals, I went ahead and multiplied the numbers by 10 to get 8:5. The 5 (carrier ratio) represents a tone that is 1/2 the fundamental--in other words, an octave lower. Here, however, I like to think in terms of a pitch class relative to scale, quite simply, in the key of C. In this case, it would be the note E. 8, by contrast, represents the note C three octaves up. What we're really talking about here is the difference of a minor 6th. So what we need to do is set the octave not 3 but 4 octaves down (oct 0) and semi up by 8 (to account for the minor sixth). That will convert the carrier ratio back to 0.5.
As you can already see, a top-down approach wouldn't take this kind of tuning into account. As we've succeeded in created a core sound by looking at the math, we'll need to continue on in the same way to get the proper ratio for oscillator 2.
The ratio here is 3:0.745. Note the carrier ratio. Thor doesn't allow anything less than whole numbers, but in some cases we can use approximations. Let's round this up to 0.75. What do we know about this? Well, 0.5 is an octave lower than fundamental. That means 0.75 (halfway between 0.5 and 1.0) is analogous to a perfect 4th below fundamental, or the note G in the key of C. What about the 3 mod ratio? Simple: It's a 12th up, or the note G. This is serendipitous. All we need to do is tune these operators in octaves and reset the oct and semi settings to get a note a 5th above our lowest partial (octave below fundamental). Very simple. Set carrier at 1, mod at 4, oct 3, semi 7.
Now let's look at the top of the chain. The ratio is 1.2:1.4. This one took me a while. I decided to look at the decimals as 10ths of an octave. This is unusual in normal circumstances because we tend to think in terms of octaves divided into 12 equal parts. We do have one convenient way into re-dividing the octave, though. The distance from one semitone to another is divided into 100 cents. So 1 octave=12 semitones. 1 semitone=100 cents. Add them up, and you get 1 octave=1,200 cents. That means that 0.1 octave=120 cents. Makes sense in theory, but how do we put this in practice?
Let's look at that ratio again. 0.2 octave (do the math)=240 cents=2 semitones+40 cents. 0.4 octave=480 cents=4 semitones+80 cents or, in Thor terms, 5 semitones-20 cents. What we're looking at here is sharp D and a seriously flat F, so somewhere in the neighborhood of a minor 3rd. This could easily be done now that we have the information we need. So even though we won't get exact results, I think what we'll have will be interesting.
To do this without resorting to some severe octave tuning not possible in Thor, I went with 6:7, or G:Bb. To get it in the right octave, the setting has to go one more lower than our target. That means 3 octaves lower or oct 1. Semi has to be a perfect 5th up, so semi 7. I chose to further tune this just 20 cents sharp.
I suppose I could also have gone 8:7 and brought the interval even closer together. It's just a personal preference of mine that inharmonic ratios have a little bit of spread to them. When I say inharmonic, remember that Thor doesn't do inharmonic ratios. They have to be created artificially within Thor by using combinations of FM oscillators that are detuned relative to each other enough to count. So even though the ratios of one oscillator are harmonic ratios, they are heard as inharmonic when used in concert with other oscillators and displaced by an octave or other interval.
Now that we are beyond our relationship issues, we need to tie everything together. Keep in mind when you use an osc to mod another osc, you should use two scalings: An envelope and a voice key note. Scaling by voice key helps alleviate some of the pitch instability that occurs in this line of work. I'd also normally route FM pairs to osc 3 pitch, but after experimenting with this for a while, I conceded that the gong sideband effect just wouldn't be pronounced enough where I needed it in the spectrum. So here's the routing: Osc2, amount 37, Osc3FM, scale 100 Mod Env, 100 Key Note. Osc1, amount 30, Osc3 FM, scale 100 Mod Env, 100 Key Note. Over in the "single" section, Amp Env, amount 29 Osc3 FM Amt; Mod Env, amount 57, Osc2 FM Amt; Amp Env, amount 28, Osc1 FM Amt.
The Mod Env. settings are: Delay 1.12 sec, A 4.63 sec, D 11.9 sec, R 10.8 sec. Amp Env. settings are: A 1.9 ms, D 19.2 sec, R 552 ms.
Only Oscillator 3 is routed to Filter 1 (bypass). You might try applying chorus to this one, but I preferred using the Delay only with no mod amount. The lower registers are more effective and noisy (don't stray below C2) while the higher octaves have a very bright, pretty asian bell kind of character. The synth crescendo is less noisy here, but doesn't really sound much like a gong. As always, these notes could be used for other kinds of effects or as inspiration for more variations of this sound.
