Sunday, 5 November 2017

Thru-Zero FM Explainer

How to get the best results from your analogue thru-zero linear FM oscillator. An explainer in response to questions about the Doepfer A-110-4, but which is also applicable to other TZ-FM VCOs.



The A-110-4 seems to be more prone to pitching artefacts than other thru-zero (TZ) VCOs. That might partly be due to the specific design, but general considerations like the tolerances and sensitivities of analogue designs also play a role. Another issue might be perception, e.g. when certain modulation depths make it hard to discern the original pitch of the carrier.

DIGITAL FIRST

Ignoring the actual implementation (frequency- or phase-modulation), the reason digital FM is easy is because it’s clean. There are no DC offsets or pitch instabilities to ruin the result.

Here is an example using the Clavia Nord Modular G2. The carrier is always heard and only the modulator is enveloped. The frequencies of the two oscillators are fixed but the FM amount is manually increased: 01-TZ_clavia-digital

The carrier was tuned to B3 and the modulator D#5. I chose these pitches by ear to show an effect which might be confused for pitching at higher mod depths. When the modulation recedes, we get a sound similar to guitar feedback. This shows that it’s possible to find combinations of frequency relationships and modulation depths that will sound ‘wrong’ even when patched digitally. In an analogue system, frequency drift or tracking inconsistencies can worsen the problem.

DIRTY SIGNALS

But weird C:M ratios are not the main problem. The real enemy of dynamic linear FM is asymmetry caused by DC offsets. If the modulating wave is not centred about zero, the sound will churn. Here’s the same G2 patch, this time with some virtual DC offset added: 02-TZ_clavia-digital_virtual-dc-offset

To avoid this, some FM inputs are AC-coupled - the signal is filtered by a capacitor. But this is not a magic bullet. If the offset is large enough and being swept dynamically, the capacitor will have a hard time eliminating it. The most likely cause for DC offsets are the modulating oscillator itself, or more precisely its wave-shaping circuitry. I have had best results with Doepfer’s A-143-9 Quadrature sine-core oscillator.

SCIENCE, SWITCHES

Analogue TZ-FM involves switching to generate ‘negative frequencies’. No matter how finely timed, there is a moment of indecision which may be audible as a growl or rumble. DC offset makes this worse as it shifts the switching point. Lower initial frequencies (aka Bias, Symmetry or LFreq) allow more modulation and brighter sounds, but the cost is lower accuracy and more ‘bum notes’.

THE A-110-4

The Doepfer TZ-VCO switches between two oscillators. This method has pros and cons. If the two VCOs do not respond equally to modulation, the resulting FM will sound ‘off’, even if the modulator is clean and the switching point is accurate. This cannot be trimmed by the user. To mitigate pitching artefacts at the point of switching, calibrating the TZ transition can help.

WHAT IS IT?

As Cynthia Webster says in her humorous video showing the difference between thru-zero and normal linear FM, without TZ “half the modulation is gone”. As you’ll hear, the frequency relationship between carrier and modulator also plays a role.



The first VCO you hear in the next two examples is the Zeroscillator, then the A-143-9 which I have modified for standard linear-FM.

If the carrier’s initial frequency is high enough and/or the modulator is higher in frequency than the carrier, the tonal result is very similar:
03-TZ-high-initial-freq_ZO-A-143-9

The real difference between thru-zero and normal linear FM is apparent when the modulator is slower. As you can see above, instead of adding gentle folds, the modulator pushes and pulls the carrier through zero. TZ allows deep levels of modulation, even when the carrier’s initial frequency is low. When this is the case, there is a big difference between normal and TZ linear FM in the possible tonal result: 04-TZ-low-initial-freq_ZO-A-143-9

One last thought on this as the Zeroscillator video is much quoted when the question “what is thru-zero FM?” is raised: toggling the “Through Zero” switch on the ZO does not yield ’typical’ linear FM; normal linear FM does not sound like this: 05-TZ-not-typical

PATCH TIPS

I have concentrated on the audio effects here, but VCOs that can go thru-zero have other uses when they themselves are used as modulators. For an idea, try this patch for a thru-zero frequency shifter and listen to your sounds swap stereo sides.

I hope this explainer helps you with your TZ-FM experiments. The files folder is here. If you’re not sure about the analogue results you’re getting and need a digital ’control’, download the Clavia Nord Modular G2 demo. If you’re on a Mac and 10.7 or higher, you can run the demo under Wine. There is info here or an installer here.

Saturday, 28 October 2017

Powwow 4 - Feedback

Here’s the recording of my live set at the fourth Berlin Powwow session which you can buy from my Bandcamp.



For this performance I wanted to explore feedback and the obstacles and modifiers one can place in the loop. The key players in this were delays, filters, non-linear functions and malfunctioning components.



My main analogue patch featured a Cwejman RES-4 in a loop with a Bananalogue Serge WVX. The combination of four frequency bands of oscillation might have been enough, but placing a Cwejman VCEQ-3 in the chain to dampen or boost the feedback added another level of complexity. A stressed coupling capacitor and scratchy Folds pot on the WVX added to the unpredictability and fun.

Live, I love my Clavia Micro Modular for two main reasons: patch recall, which allows me to set a scene or chop between moods, and polyphony. The virtual feedback patches in this set were simple, but switching them to two or three voices added complexity and interest, for example asynchronous panning or the beating of multiple sine-wave oscillators. You can do it with a ’real’ modular, but at a cost!

This set up is flexible and just about portable. It’s still completely live in that each patch either has to be built or played by hand. But the addition and convenience of the Micro Modular does cause me to question how we approach playing live with a modular. With many musicians turning up to gigs with their rigs pre-patched, is there a difference or even a need for the real deal?

Thanks again to Goldwiener, Hainbach, Paul da Fonk and Mark Berman of Powwow for the opportunity to make some noise.

Thursday, 19 October 2017

Basic Electricity Concert Tonight - Rastko, Plastiq Phantom



If you’re in Berlin tonight, come along to Basic Electricity, a concert with the Serge Animal tamer, Rastko and Patch Point proprietor, Plastiq Phantom, aka Dr. Wiener.

Doors open at 19:30 for music at 20:30 at the König Otto in Neukölln. As you can see, it’s an amazing venue housed in the old Kindl brewery.

There’s more info here and a Facebook event here.

See you later!

BE#23, Thursday, 19.10.17 @ König Otto
Tickets 10€. Doors at 19:30, music at 20:30
Am Sudhaus 3, 12053 Berlin Neukölln
U7 Rathaus Neukölln or U8 Boddinstr.

Wednesday, 27 September 2017

Basic Electricity - concert, tomorrow night in Berlin




Basic Electricity returns tomorrow night with a special concert featuring Michael Vorfeld’s Glühlampenmusik and Wouter Jaspers’ Field Trip at the König Otto in Berlin, Neukölln - come along at at 20:00 for what promises to be an audio-visual treat!

There’s more info at the Basic Electricity Blog and here is the Facebook Event.

Here is Wouter performing with some of his Koma gear at Powwow last week:



Look forward to seeing you tomorrow night at Basic Electricity!

BE#22, Thursday, 28.9.17 @ König Otto
Am Sudhaus 3, 12053 Berlin Neukölln
U7 Rathaus Neukölln or U8 Boddinstr.

Tickets 10€. Doors at 20:00, music starts 21:00
Seating is limited to 50, so please come on time.
The bar will be open for drinks and sandwiches.

Thursday, 29 June 2017

Take Seven - modular jazz revisited

A longer improv and edit inspired by this modular bebop sketch.



This track started out as a test for my old Boss SE-70 Super Effects Processor - the kitchen sink FX box from the 90’s, loved by The Prodigy - which I had dusted off to check out the pitch shifters.

A medium-paced Wogglebug conducted two Plan B Model 15s and Maths. There was a bit of FM and wave-folding involved. I’ve always felt that the Wogglebug had the jazz so it was a short jump of the imagination to add some Rhodes/ Cwejman RES-4-ish tones from a Clavia G2 Voice Filter patch and some brushed beats.

I guess this was an exercise in re-contextualisation - hope you enjoy it!

Wednesday, 28 June 2017

Powwow - Thanks 2

A second round of applause for hosts Hainbach & Goldwiener and their lovely assistant Paul Da Fonk for a fab time at Berlin’s 2nd Powwow stream at Patch Point!



Here’s the recording of my set which you can also buy from my Bandcamp:




Get ready for the 3rd Berlin Powwow event, also on Youtube, on Friday, July 21st with music from Ashley M Puente, Hainbach, Goldwiener, Lindred and Navs and featuring the knock-out visuals of Luma //Chroma!

Thursday, 8 June 2017

Navs Live on Berlin Powwow Stream Tonight!



I’m taking part in the second Berlin POWWOW live video stream this evening, Thursday, 8th June. It’s a live modular improvisation over the internet also featuring Andrea Lange, Hainbach, Goldwiener, a special surprise act and visuals by Luma //Chroma.

The first Berlin session was loads of fun - join us for part two tonight!