Invisible Man wrote:
Oh, for the love of God, please do. Please. I wish I had a brain for this kind of thing, but need someone to spell it out for me.
HighDeaf1080p wrote:I believe it is in the Key9 demo that Rupert says, "it behaves just like your guitar's sound, because it IS your guitar's sound." That, to me, also indicates that they are processing the guitar's signal the same way a synth processes its oscillator.
Okay so I'm going to throw out a little bit of physics and go from there. Also let me say that I haven't confirmed any of my theories about the operation with EHX or anyone who worked on it but based on being in electrical engineering school and years of synth and sound nerdery this is what I think is happening.
When you hit a note on a guitar, there are essentially 2 portions of the note. The first is the transient or the attack. When your pick or fingers hit the strings, there's a blast of essentially unpitched noise at the very beginning of the note. After that, the string vibrates at whatever frequency is defined by it's tightness/your fretting/a capo/acts of god/etc. Historically, the transient has always been a big problem in guitar synthesizers. Because it's essentially noise, a guitar synth that listens to your input signal and tracks it to create a MIDI or CV value that then controls a synthesizer has to either wait a few milliseconds for the transient to be overtaken by the actual note or it just says fuck it and glitches out. As an analogy, think of a sample and hold: you take a noise source and sample it at a given time, you get an effectively random value-the guitar synth counts the number of oscillations and interprets that as a note value, and if you feed it noise it doesn't know what to do because it's not a periodic waveform that has an actual note.
Quick mathematical diversion: All signals can be represented as a series of sine waves. This is called the Fourier series, and it is HELLA crucial to a couple of pieces in this discussion. When we talk about a sound having a lot of harmonics, we're talking about that sound having lots of components in it's Fourier series representation. The sine wave with the biggest amplitude value is the fundamental, and all of the other harmonics are quieter than it. The Fast Fourier Transform (FFT) is an operation that can be performed on an incoming signal to break it down into it's fourier series components. If you've ever looked at a spectrum analyzer, you're seeing an FFT or some variation on it.
ANYHOOT now is where EHX comes in. The Spectral Gate from the HOG line is fucking brilliant. If you have the chance, play a HOG or HOG2 and compare the sound of it with and without that. With it off, there is a lot of """""ringing""""" and interesting harmonic action. The processing is of the full spectrum of the input notes. So, if the input has a lot of harmonics, the resultant operations can get kind of mushy, because the pitch shifting is being done not just on the fundamental note at the input, but also on everything else-all of the harmonics. What Spectral Gate does is it performs an incredibly fast filtering operation on the input signal, the result of which is basically a sine wave or a very simple waveform with very few harmonics. This comes in handy later. I'm fairly certain that the Spectral Gate is a very fast changing bandpass filter that starts with an extremely wide bandwidth and filters until only the fundamental exists at the input. Mathematically, to connect this to the FFT previously mentioned, the goal of this is to reduce the amplitudes of all of the harmonics that are not the fundamental until the spectrum analyzer has a single line on it representing the amplitude value of the fundamental.
SO, to recap, we've got a guitar signal on the input, which has a transient portion and a sustaining portion, and we've used Spectral Gate or something similar to it to filter it down to being a sine wave or very close to a sine wave. And that, is where the fun happens
I believe that what EHX does now is they have a series of equations that, when fed a sine wave input (or a series of sine waves representing a bunch of notes played together), produce an output that sounds like [insert your favorite 9 series sound here]. Organs are easy to create with these equations. If you sit down at a Hammond Organ and play a C with all of the drawbars pulled out to their maximum (the best setting), you'll hear a huge note with tons of harmonics. That note doesn't do anything complex-it's constantly a bunch of C harmonics at volume levels set by each of the drawbars with no amplitude change over time unless you hit it. A Rhodes or Wurlitzer is a little bit different-they have a natural decay, but so does a guitar so that saves some hassle. The Mellotron sounds are a bit more complex, but if you've got a simple sine wave on the input and you perform an unholy amount of wavefolding/multiplying, octave shifting, filtering, EQ'ing, and other processing to it, it won't sound like a sine wave at all anymore, it will sound like whatever you want it to be and since all of the processing is based on a live input of a sine wave with no harmonics, there's no need to worry about whether you're playing within the confines of the 12 note piano keyboard. You can feed a sine wave at 440 Hz and the processing will turn it into whatever, and you can feed a sine wave at 446 Hz in and it will become whatever-no pitch bend information, no bullshit, just extreme processing. It's like what we do with all of our pedals but with a lot more math.
BUT WAIT WHAT ABOUT THE TRANSIENT! said someone I placed in the audience to ask a question to hold me accountable. All instruments have some kind of transient or attack portion of their signal. On a Hammond organ, it's the famous key click. On a flute it's the "chiff" of someone making the blowy blowy across the mouthpiece. For the 9 series, I think what they do to work with the transients is that while the Spectral Gate is settling on the fundamental, they have a different set of equations that process the first bit of the note to generate a believable transient.
Experimental data to back this up:
-For a long ass time I had an MXR Dyna Comp set to some ridiculous hyper compression shit before my C9, and I noticed that it sort of gave the effect of "overblowing" when I had the C9 set on the Mello Flutes setting. I'm pretty sure that what's happening is because the harmonics and fundamental are made that much stronger and louder for a longer time by the compressor, the Spectral Gate gets sort of confused and you get some really weird (really awesome) stuff with that particular setting. Can't remember it being all that hot on the other settings but with the Mello Flutes it added this sort of raunchy grunge that works amazingly well.
-I'm not actually a real guitar player but I have a Moog Guitar and most/all of my experience with the 9 series is with it as my guitar input thingy. This is an important thing to note because with the ability to sustain a note forever comes some interesting discoveries when playing something like a C9. If you play an infinitely sustained note into the C9 and then make another note bloom up (very easy with the Moog Guitar-I used to spend a lot of time just holding a note or two high up with my left hand and reaching down to tap out other notes with my right hand on other strings) while that one is still sustaining, the C9 takes a second to adjust to what the new note is, and I think that's because the spectral gate is fighting to keep the input signal a sine wave at the first note's frequency and needs to be absolutely certain that the new frequencies coming in are a new note and not some garbage on the input.