Synth Guitar by Alfonso D'Amora

Creator

Picture  (Click to enlarge)

Creator's description

"A true analog synth drivable from any sound source."

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Mod1  Mod2

   

Signal Flow: Here  
DSP: 1 voice takes approximately 1 Sharc chip. Versions of this patch exist for Modular I & II. 
Samples:    

Notes from the creator of the patch - Alfonso D'Amora:

"This is not a filter. This is a true analog synth drivable from any sound source, keeping its own sound almost regardless of sound source spectrum. 

Of course range, dynamics, levels, playing technique of the sound source affects the synthesizer's response, but for example if you sing some vocals, words will never be audible (like in vocoder or in simple filtering).
This synth accepts mostly monophonic lines, but can be great in power chords, especially on 4th, 5th and 6th strings.
As this patch is using modules playing unusual roles, two things are recommendable:
The bandpass filter immediately after audio ins acts as an harmonic content reducer to get the proper oscillator synchronization, so if you want a tonal response, resonance must be off.
The tuning of the sync'ed oscillator is better on low range. Of course great effects can be achieved otherwise."

"It's basic concept is to filter an incoming audio signal so as to get the narrowest band passing (24db bandpass), as to get defined root frequency with the least overtones. 

These overtones are shaped by tweaking the frequency of the filter. The result is used to synchronize a slave sine oscillator. As the master signal contains overtones, these affect the final wave produced by the Oscillator."

 

Description

So how does this patch actually work? When you first plug a guitar in to drive it, you'd could easily think that the patch is just working as an effect unit, altering the sound that you send in, and passing it out again. This is in fact not the case. None of the original input is sent to the outputs - instead the audio input drives the Sine Oscillator. The final output is heavily dependent on the characteristics of the incoming audio, but is not just an effected version of it.

Take a look at the signal flow diagram.

 

For now, let's just concentrate on the modules in between and below the two Envelope Followers. We can ignore everything to the left of these modules for now as these are purely Amp and Effect modules and aren't so fundamental to our understanding of how this patch works. We'll return to them later.

Following the path from the Audio In, you can see that the signal is initially sent to four modules. Ignoring the VU module which has no effect on the output of the patch, we can see that the Audio goes separately to  2 envelope followers and a 24db Bandpass R filter. You can see from the  diagram that Envelope Follower 1 is used purely as a modulation source for the filters, so lets look at the Bandpass Filter R and the Envelope Follower 2.

 

The signal coming into the BandPass R is heavily filtered -  the presets mostly have Resonance set to zero, allowing only a very narrow band spectrum through. This means that most of the harmonics except the fundamental are filtered out, which gives the Sine Sync OscS a nice 'clean' signal for it to lock to. The Cut Off of the filter can be tweaked to alter the band of frequencies which are allowed through.

The output of the 24db Bandpass filter is fed to the Sync input of the Sine Osc S module. As sync'ed Oscillators get their root frequency from the Sync Input, the frequency of the signal coming out of the filter will give the Sine Osc it's pitch. Meanwhile, the output from Envelope Follower 2 feeds the Frequency input of the Oscillator. This might seem counter-intuitive, but all this is really doing is 'exciting' the oscillator - it's not deriving it's pitch from this signal, just being energised by it. The oscillator responds to the signal from the Envelope follower in such a way as it responds in the same way as the source. If you're feeding a guitar signal in, the corresponding output will have many of the nuances of the original instrument.

 

The output of the Sine Osc Synth goes separately to the Multimode filter, and the Uknow filter. The output of the Multimode filter is then fed into the Vocal filter, and then the output of the Uknow and the Vocal filters are mixed down into a single output using the Mix2 module.

 

Each of the above filters receives a modulation signal from both of the envelope followers as follows:

The Uknow filter can have its Cut Off modulated by Envelope Follower 1, 2 or both.

Similarly the MultiMode filter can have its Cut Off modulated by Envelope Follower 1, 2 or both.

The Vocal Filter can have Vocal Position modulated by both envelope followers and FM (Frequency Offset Modulation) modulated by Envelope Follower 1.

This means that you have a great deal of control over the shape of the filter that the signal passes through - you can create different modulation envelopes using the settings in the different Envelope followers, have the filters modulated by varying amounts of these envelopes and then recombine as much or as little as you like of each signal in the mixer.

 

After the Mix2 module, the signal passes through a 12db gain module and then a Linear VCA Amp, which is modified by Envelope Follower 2. From here, the signal passes through a fairly conventional path of modules - 12db Lowpass filter, 12db HighPass filter, Delay, Phaser, Chorus and finally the signal is sent through two Mono limiters, one for each channel of the Stereo Chorus, before reaching the audio outs. 

 

There is also a Modular 1 version of this patch available on PlanetZ. It is almost identical in principle to the Modular II version, differing in only a couple of modules. There's one sample in the samples section using the version 1 patch.

 

Here are some more notes from Alfonso on the patch:

Many of the things I discovered were just a matter of luck, and I tried many routings before getting the right one.

Something that helps me a lot is to search online info on modular synths of any type. In this case I've read that sync'ed Oscillators are restarted in their cycles by the incoming sync signal via the sync input. Thus they get the root frequency from there.

On the other side the frequency tuning of the sync'ed Oscillator modifies the wave that will be re-clocked from the sync input, so acting like a shaper. The technique of ring modulation was created to bring power and to expand the timbral possibilities beyond the limits of subtractive synthesis (vco+vcf). 

Practically this seems to be a good way to have control on overtones keeping a given root.

The 24db bandpass filter is used to put in evidence the root of the incoming sound and to get the narrowest bell around it, in this way making sufficiently uniform the products of filtering of different sources. 

This seems to allow different sounds to play the presets as they are. Unlike the filters coming after the Oscillator this one  is not used to colour the sound but to de-colour the incoming signal.

Resonance must be of course at zero for the cleanest results (but you may need dirty ones....)

At this point we must say that both the band-passed source and the Oscillator tuning in their specific relation generate a very rich wave. So I chose a sync sine, that avoids redundancy and can produce almost any shape when re-clocked. Of course you can act on both the frequencies of the 24db bandpass filter and of the oscillator getting a great number of interactions.

The envelope followers are used to get the power to excite the oscillator and to modify some filter parameters and of course to drive the VCA.

The way the unusual routing of the envelope follower to the Oscillator frequency input works to excite the oscillator, I can't explain , but I've always thought that many signals in the modular are similar, and you know that the unusual routing belongs to the history of pulsar modular..., the signal that's coming out from an envelope follower should be not so different from the original, it's modified (and i don't know how) to reproduce/alter and provide its dynamic content to another operation and this consideration pushed me to try this solution. I was lucky on that.

 

Samples

 
Genova 2001 1.34 MB Here's a full length composition by Alfonso which features the Guitar Synth extensively, along with other patches made by Alfonso - 'Azzhatz' & 'Heavy Machinery'.
Matrix (Arrivals) 310 kb Arrivals patch triggered by electric guitar 
Glide (Arrivals) 458 kb I'm no better a singer than a guitar player, but you can get some great vocal effects with this patch!
That Touch 83 kb This one is triggered by a clean Electric Piano sound.
M1 solo 148 kb The version 1 patch triggered by an acoustic Piano.

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