hARMONIC experiments

Playing around with the Verbos 262v

I'm surprised how many vactrols it uses.

View this post on Instagram

#buchla262v #harmonicoscillator #buchlaformat Self generating patch ..Sorry about the sound quality.. just my camera phone.

A post shared by jono (@dj_jondent) on Jan 27, 2019 at 7:56pm PST

Apologies for the poor sound on this instagram video, but it does sound really amazing.
I'll do a proper recording one of these days.

It started me wondering how many other "harmonic" related VCO modules there are out there.
Not may I think.
In Euro the The Verbos Harmonic Oscillator (HO), the Mutable instruments Plaits & Braids and the Make noise Telharmonic were some modules I could find. The HO looks related to the Buchla 148, 262v.
Do let me know if you know of any other modules that you think fall into this category.
The old Hammond organ with its drawbars is an example of this type of synthesis (additive synthesis).
In the software world Native Instruments Razor is a good example.
This brings up the topic of additive vs subtractive synthesis.
and begs the question why are there so few Synth modules that do additive synthesis?

The other euro module that I think can be loosley added to this list is the Make Noise Echophon.

The Echophon's depth control of the pitch shifter can be used to roughly approximate the harmonic series of the imputed  audio .. these are the frequencies that are multiples of the fundamental. To do this the large black pitch control knob must be set to max.

Every musical sound has these harmonics. A sine wave has only the fundamental or first harmonic, a saw tooth contains all harmonics in inverse proportion to their number. A square wave has all the odd harmonics in the same ratio, etc etc.
So with the Echophon, we can for example, just use a sine wave which has only the fundamental harmonic, and then add more harmonics by turning the depth control knob (the blue one).

Maybe this is use of pitch shifting modules to obtain spectral shifting is worth further investigation.
I understand that shifting the pitch of signal components retains their harmonic relationships.
----------------------------------------------------------------

Other modules worth exploring are clock dividers & multipliers .
Eurorack modules in this category include the SSSR Labs VC Divider, the 4MS Atoner, the quad clock distributor, the RCD (rotating clock divider) and SCM (shuffling clock multiplier). Use audio-rate input sources instead of LFOs with the clock dividers & multipliers to get harmonically related outputs.

The Doepfer A-137 is worth a look at.

The basic idea of a wave multiplier is to multiply the waveform of an incoming signal (e.g. triangle/saw/sine from a VCO) within one period of the waveform. This leads to additional harmonics of the incoming signal. The period and consequently the pitch of the signals remains unchanged.
The A-137 works as a kind of "inverse low pass filter", i.e. it adds a lot of harmonics to a signal that contains none or only a few harmonics (e.g. sine or triangle waveform). In contrast to that a low pass filter (e.g. A-120) removes harmonics from a signal that contains a lot of harmonics (e.g. saw or rectangle waveform).
 -------------------------
Ladik make a Harmonic Generator in 8 HP
The H-020
 ------------------------

A little bit  more off this topic, but still  loosley related are filter bank style modules.
I think the Verbos Bark Filter, and the Frap Tools Fumana are worth investigating.
The Bark/Fumana seem to be inspired by the Buchla 296/295/294.
Also worth a google are the 4MS Spectral Multiband Resonator (SMR) and the Serge Resonant Equalizer.

Re the Buchla 294/295/296, the Verbos Bark, the Fumana, the 4MS SMR and the Serge Res Eq. ... maybe they can be better described as "spectral processors"..... they are much much more than fixed-filter banks.

 

 The 294 comb filter is on the extreme left.

 The 295 filter

The first two, the Buchla 294 & 295, Don called comb filters, but their evolution into the amazing 296 seems plain to see.

The 296, the Fumana and the Bark are 16-band filter/spectral analyzers. Amazing tilt-like controls, you can address odd and even bands. They also have a row of envelope followers -- one per band.

Mark Verbos has chosen to use the "Bark scale".
It is named after Heinrich Barkhausen who proposed the first subjective measurements of loudness.
The scale ranges from 1 to 24 and corresponds to the first 24 critical bands of hearing.

 The Frap Tools Fumana - Dual16 Band Spectral Editor

The outward style of each of these modules is very similar ... the upper section provides access to each filter's main output at the chosen fixed frequencies.

The Buchla 294 uses the scale:
<250/ 1K / 4K / >4K

The Buchla 295 uses the scale:
<100/ 200/ 350/ 500/ 700/ 1K/ 1.4K/ 2K/ 3.5K/ >7K

The Buchla 296 uses the scale:
<100/ 150/ 250/ 350/ 500/ 630/ 800/ 1K/ 1.3K/ 1.6K/ 2K/ 2.6K/ 3.5K/ 5K/ 8k/ >10K

The Frap Tools Fumana uses the scale:
 15/ 65/ 90/ 122/ 170/ 230/ 320/ 435/ 600/ 825/ 1.1K/ 1.5K/  2K/ 3K/ 4K/ 5.5K/ 22K

 The Verbos Bark filter uses the scale :
<100/ 300/ 510/ 770/ 1.08K/ 1.48K/ 2K/ 2.7K/ 3.7K/ 5.3/ 7.7K/ >10.5K

The published Bark band edges are given in Hertz as [0, 100, 200, 300, 400, 510, 630, 770, 920, 1080, 1270, 1480, 1720, 2000, 2320, 2700, 3150, 3700, 4400, 5300, 6400, 7700, 9500, 12000, 15500].

So the Verbos Bark uses every second Bark band.
Looks like the Frap Tools has more evenly spaced bands following something like a graphic EQ, whereas the Verbos focuses on frequencies that are more recognised by the ears.
The Fumana might be better for shaping bass sounds as it has 3 bands below 100Hz, but the Bark may be better for singling out harmonics that the human ear can distinguish ???

Quote: Fumana manual.
"Each of the two filter array is based on 16 parallel analog bandpass filters. The main filter bands from 2 to 15 are mainly based on Bessel calculation, while bands 1 and 16 are respectively a lowpass and highpass with a custom method to obtain better musical results. All bands on the main filter array use an 8th order slope (48dB/oct)." 

Links:
+ Top Octave Generators
+ Muffs - DIY Harmonic Osc