Let's Design and Build a (mostly) Digital Theremin!

"D-Lev looks cool "  - Buggins"Good show! Schwimmer's a great musician to showcase the D-Lev"  - bendra

I wonder if anyone could tell that it was a D-Lev?

I think your logo may be even bigger than Moog’s on the Claravox

"I think your logo may be even bigger than Moog’s on the Claravox"  - bendra

It's easy to go too big I guess.  Roger originated the nice D-Lev logo, and I use a slight variation of it as a smaller 3D printed & spray painted plate for the kits:

Lotus  + Trixie + Flamma

Other than some kit work and some software improvements, the only thing I've done lately is play:

1. Rob Schwimmer's incredibly addicting version of "Lotus Blossom",
2. with Trixie, a somewhat younger variation on the patsy preset, through
3. the Flamma FS02 reverb pedal.

https://d-lev.com/audio/2022-04-15d_trixie_lotus.mp3

The very last note is played with my hand resting on the pitch plate itself.  And recording through a reverb keeps one "honest" because you pretty much have to do it in one take with no editing (though I did some noise reduction in Audacity).

From the excellent observations of Eli and Vincent, both D-Lev kit owners, I removed the octave offset from the oscillator section and incorporated it instead into the general pitch processing gauntlet.  So presets which rely on pitch tracking modulation of formants and filters are now bank switchable without falling apart (indeed, I bank switch Trixie half-way through that clip above using the new code).  Those presets will need some massaging though, and I'm looking into automating it in the librarian.  I readdressed the new pitch processing "Lift" knob code as well for the 10th time and am happier with it. 

Ideas for basic improvements to the design are always quite welcome!

The Left Banke

The pitch transposition / modulation logic feels like it's reached a topological entropy minima that can't be merely local.  While trying to convert the presets to the new pitch modulation scheme, I realized a "bank" knob would make the transition almost completely painless.  So on the main "D-LEV" screen the "oct[-7:7]" knob has been replaced with a new "bank[-3:3]" knob, which offsets the global pitch reference up to +/- 3 octaves.  The "bank" knob offsets the LED tuner, the triple oscillator, pitch preview, MIDI, and any parameters being actively modulated via pmod.  The "bank" knob is used to transpose voice presets while retaining the proper alignment of all pitch-based elements that constitute them.

The violin_2 preset sounds mournful with (you guessed it!) some Flamma reverb: https://d-lev.com/audio/2022-04-17_violin_2_over_jordan.mp3

Hi everyone, I'm a novice in this group and as theremin player. I post my question here and I apologize if I did it incorrectly. I would like to build my first Theremin using Eurorack modules, I saw that the only solution is with two Doepfer's theremin modules ... what do you recommend? Better with an Etherwave or another instrument and use any other system with CV in to widen the the Theremin's sound? I started with a Theremini but I was not completely satisfied with its playability and for study it. Congratulations to the group ... it seems nice to me.
Thanks in advance to those who want to help me

Hi everyone, I'm a novice in this group and as theremin player. I post my question here and I apologize if I did it incorrectly. I would like to build my first Theremin using Eurorack modules, I saw that the only solution is with two Doepfer's theremin modules ... what do you recommend? Better with an Etherwave or another instrument and use any other system with CV in to widen the the Theremin's sound? I started with a Theremini but I was not completely satisfied with its playability and for study it. Congratulations to the group ... it seems nice to me.Thanks in advance to those who want to help me

Hi Weckler,
welcome to the TW forums. I think you can better open a new topic with your question in Theremin Newcomers or Theremin General, as this thread discusses Dewster's D-Lev theremin. I'm reading you're not planning to build a (analog or digital) theremin from scratch but are concidering existing modules or intruments featuring CV out to combine or integrate with a Eurorack setup.

Thx !

Maximize Control With Minimal Movement

I've been thinking about this for a while and I think it's generally true.  With the Theremin, you want to use the smallest movements that still allow full control over your performance, and this applies to both the pitch and volume fields.  When I say "full control" I'm also including stability factors, so even if you could easily play octaves by cricking your pinky finger, you wouldn't be able to just casually stand and play at the thing because your body, arm, or even hand would need bracing of some sort to keep the pitch steady.  So stability seems to dictate the upper end to sensitivity - clearly someone who sits to play is literally in a better position to manage the typically overly tight (IMO) analog pitch field, and those who like to stand may benefit from a looser pitch field. 

The volume field situation is more complex, here the application of appropriate non-linearities such as a gain-switching "knee" and second order drop at lower volumes can allow one to go from total silence to significant audibility (say -12dB) with a relatively small movement of the hand, and from there to full volume (0dB) with a similarly small hand movement, thus devoting more detailed hand movement to the meaningfully expressive region by compressing the inexpressive region.

Absorptive All-Pass Reverberator

Was re-reading some reverb design papers, and ran across the "absorptive all-pass reverberator" which incorporates a first order low-pass filter in the direct path of an all-pass multi-delay filter.  The Inharmonic Resonator in the D-Lev gets rather metallic with high feed-forward / back settings of the all-pass, so I limited the knob to +/- 1/2 full scale in order to minimize this, but there are interesting effects to be had with higher settings.  Yesterday I moved the comb filter low-pass feedback filter to inside the nested all-pass filter, and it seems to have improved things somewhat:

Above is the new topology.  The usual first order low-pass with safely bounded accumulation is used.  The overall comb is formed by delay z^-m and feedback gain km, the inner nested all-pass is formed by delay z^-n and feed-forward / back gains of kn, with the feed-forward subtracted.  Both km and kn are signed controls, and distinctly different sounds can be obtained by flipping the signs of the feedback.

The wildcard here is setting the cutoff frequency of the low-pass filter.  A dedicated knob would be the most flexible, but in fact lowering the cutoff is very similar in effect to lowering feedback gain.  I ended up subtracting kn^2 from km^2 and running this through the 4th order polynomial described in a previous post.

Not an earth-shattering change to the Resonator, but an improvement, and good practice for future reverb design work, where a cascade of these units might fill the bill.

Hi,

Is it in the new software load ?
(2022-05-04)

Just to see how does it impact settings and sound.